1C,. · I I BARLEY SILAGE HARVESTED AT BOOT AND SOFT DOUGH STAGES FOR LACTATING COWS by Yamandu M....

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BARLEY SILAGE HARVESTED AT BOOT AND SOFT DOUGHSTAGES FOR LACTATING COWS

by

Yamandu M. Acosta

Thesis submitted to the Faculty of theVirginia Polytechnic Institute and State University

in partial fulfillment of the requirements for the degree of

Master of Science

in

Dairy Science

APPROVED:

.1C,‘Q j ”hfI{ß //Charles C. Stall ngs, Carl E. Polan

Chairman

Roanld E. Pearson Vivien G. Allen

Daniel E. Brann William E. VinsonI

IApril, 1969 I

I Blacksburg, Virginia I‘ I

I IIII II II_ _ _y ‘ I

BARLEY SILAGE HARVESTED AT BOOT AND SOFT DOUGH STAGES

FOR LACTATING COWS

byYamandu M. Acosta

Committee Chairman: Charles C. Stallings

Dairy Science

(ABSTRACT)

Barley (Hordeum vulgare, L.) harvested at boot (5/7/88) and

soft dough (6/6/88) stages of maturity was ensiled for

nutritive comparisons. Boot stage was wilted and soft dough

was direct cut at 15 (SD-Lo) and 25 cm (SD-Hi) above ground.

Yields (kg DM/ha) were 3690, 8750 and 6287 for boot, SD—Lo

and SD-Hi respectively. Digestibilities (%) of DM, CP andL

ADF were 74.7, 74.5 and 70.8 for boot; 61.9, 50.4 and 44.7

for SD—Lo; and 62.3, 47.2 and 49.7 for SD—Hi, respectively.

'Calculated TDN was 71.2, 62.0 and 62.8 for boot, SD—Lo andSD-Hi, respectively. Thirty—six lactating Holtein cows were

fed boot silage at 75 and 60% of diet DM, SD—Lo fed at 75

and 60 and SD-Hi fed at 75 and 60, respectively. Milk yields

(kg/d) were greatest for high concentrate diets and averaged

25.7, 28.3, 24.8, 26.3, 25.7 and 26.9, respectively. There

were no differences among diets for DM intake or 4% FCM.

Boot silage had a greater In Situ rumen degradability of DM, ;CP, ADF and NDF (68.6, 89.3, 44.2 and 45.1% respectively) Ethan SD-Lo (57.8, 76.9, 20.9 and 24.2%) and SD—Hi (62.5,80.0, 22.8 and 26.4%). Predictability of ruminal degradabil-ity of complete diets from weighted averages of singleingredients determined separately was low. In Situ incuba—tion of single ingredients resulted in underestimation of DMand overestimation of CP degradability compared with com-plete diet incubation.

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rolled in a graduate program.

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TABLE OF CONTENTS

pageABSTRACT ............................................ iiACKNOWLEDGEMENTS .................................... ivLIST OF TABLES ......................................viiiINTRODUCTION ........................................ 1LITERATURE REVIEW ................................... 3

1. Introduction .................................... 32. Stage of Maturity and Total Dry Matter Yield .... 3

3. Stage of Maturity and Composition ............... 4

4. Effect of·Cutting Height ........................ 9

5. Effect od the Ensiling Process .................. 9

6. Effect of the Diet Characteristics andComposition on Milk Yield ....................... 14

6.a. Dry Matter Intake ............................. 146.b. Energy Intake ................................. 19

6.c. Protein Intake ................................ 227. Effect of the Diet on Milk Composition .......... 31

MATERIALS AND METHODS ............................... 36

1. Field Trial ..................................... 36

2. Silage Evaluation ............................... 40

3. Heifer Digestibility Trial ...................... 43

4. Lactating Cow Feeding Trial ..................... 47

5. Ruminal Degradability Study ..................... 50

RESULTS AND DISCUSSION .............................. 551. Field Trial ..................................... 55

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2. Silage Evaluation ............................... 58

3. Heifer Digestibility Trial ...................... 69

4. Lactating Cow Feeding Trial ..................... 73

5. Ruminal Degradability Trial ..................... 84

SUMMARY AND CONCLUSIONS ............................. 103

REFERENCES .......................................... 106

APPENDIX ............................................ 114

VITA ................................................ 120

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LIST OF TABLES

table page

1 Planting date, seeding rate (kg/ha) and

fertilization date and rate of the barley

fields used in the experiment .................. 37

2 Growth stage, cutting height (cm), theoretical

lenght of cut (cm) and date of harvest of the

treatments ..................................... 38

3 Experimental diet composition in terms of

barley silage source and forage/concentrate

ratios (dry matter basis) ...................... 48

4 Yield (kg/ha) and content of forages harvested

at two stages of growth and two cutting

heights ........................................ 56

5 Dry matter and fiber fractions of the three

silages ........................................ 59

6 Crude protein content (CP), N insoluble in buffer

(BUFFINSOL—N), buffer soluble N,neutral detergent

(NDIN) and acid detergent (ADIN), total water

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soluble N (WSN) and water soluble true protein

(WSTP), of the three silages ................... 61

7 Lactic and major volatile fatty acids and pH of

the three barley silages ....................... 64

8 Calcium, phosphorus, magnesium, potassium,

sodium and sulfur content of the three silages

as % of the dry matter ......................... 66

9 Dry matter, crude protein, neutral detergent

fiber and acid detergent fiber recovered from

the silos as % of the original amounts stored

for each of the barley treatments .............. 68

10 Dry matter, proximate components and acid and1

neutral detergent fiber fractions of the

composite samples of the silage treatments

fed during the digestibility trial ............. 71

11 In Vivo apparent digestibility of silage

fractions and Total Digestible Nutrient

content of the three barley silage treatments .. 72

12 Dry matter (DM), crude protein (CP), total

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digestible nutrients (TDN), net energy for

lactation (NEL) and acid detergent fiber

(ADF) contents of the experimental diets ....... 74

13 Dry matter intake (DMI), dry matter intake as

% of body weight (DMI/BW), milk yield (Milk)

4% fat corrected milk yield (4% FCM), milk

. components (Fat, Protein, Lactose, Solids Non

Fat and Total Solids), Gross Efficiency, Energy

Efficiency, body weight change (BWChange),

intake of total digestible nutrients (TDNI),

and acid fiber detergent intake (ADFI)

associated with experimental diets ............. 76

14 Dry matter intake (DMI) kg/d and as %BW

(DMI/BW), milk yield (Milk), 4% fat corrected

milk yield (4% FCM), milk components (Fat,

Protein, Lactose, Solids Non Fat, and Total

Solids), Gross Efficiency, Energy Efficiency,

body weight change (BWChange), intake of total

digestible nutrients (TDNI) and acid detergent

fiber intake (ADFI) of the experimental diets

grouped by forage source and forage/concentrate

ratio .......................................... 78

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15 Correlation matrix for dry matter % (DM),

totaldigestiblenutrients % (TDN), acid detergent

fiber % (ADF), milk yield kg/d (Milk), 4%

fatcorrectedmilk yield kg/d (FCM), milk fat (Fat),

dry matter intake kg/cow/d (DMI), TDN intake

kg/cow/d (TDNI), ADF intake kg/cow/d (ADFI) and

body weight change kg/cow/d (BWCH) associated

to experimental diets .......................... 81

16 Ruminal degradability parameters, A, B, C, D

and Kd for the dry matter of the experimentalsilages ........................................ 84

17 Ruminal degradability parameters (A, B, C, D,

and Kd) of nitrogen compounds of the

experimental silages ........................... 86


and Kd) of the Acid Detergent Fiber (ADF)

fraction of barley silages ..................... 88


and Kd) of the Neutral Detergent Fiber (NDF)

fraction of barley silages ..................... 89

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and Kd) of the dry matter and nitrogen of the

Soybean Meal (SBM) and Shelled Corn (SCorn)

used as concentrate ingredients of the

experimental diets ............................. 91


and Kd) of the dry matter of the experimental

diets .......................................... 92


and Kd) of the nitrogen ccmpounds of the



and Kd) of Acid Detergent Fiber (ADF) of the

experimental diets .............,............... 95


and Kd) of neutral detergent fracticn (NDF) of

the experimental diets ......................... 97

25 Composition of the experimental diets expressed

as percent of each ingredient in a dry matter1

basis .......................................... 98

26 Predicted parameters of ruminal degradability

(A, B, C, D, and Kd) of dry matter of the


27 Predicted parameters of ruminal degradability

(A, B, C, D, and Ka) of nitrogen compounds

of the experimental diet ....................... 102

TABLES IN APPENDIX

A1 Macro and micromineral contents of barley tissue

sampled from the three fields of the experiment

on 4/01/88 ..................................... 115

A2 Composition and nutrient content of the

pre—experimental diet used between 6/27/88

and 7/13/88 .................................... 115

A3 Nutritive composition of the concentrate

ingredients used in the formulation of the


A4 Composition of the mineral mix (VPI Dairy

Mineral) supplemented in the feeding trial

and In Vivo digestibility trial ................ 116

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A5 Nutritive composition of the barley silage

used during the pre—experimental period of

the In Vivo digestibility trial ................ 117

A6 Typical analysis of variance table for

yields and composition of the harvested

material of the field trial .................... 117


silage composition ............................. 117


digestibility coefficients of proximate

components and TDN content of the silages ...... 118

A9 Analysis of variance table for milk

production, milk components, dry matter

intake and body weight change .................. 118

A10 Analysis of variance table to test milkproduction, milk components, dry matter

intake and body weight change according

to forage source and concentrate level

of the experimental diets ...................... 118

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A11 Average monthly temperature (QC) and total

precipitation mm (rainfall and snowfall) of

the growing period of barley crop and feeding

experiment ..................................... 119

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INTRODUCTION

Small grains are the most commonly used spring crops

for silage making in Virginia. They are reliable and well

adapted to the Virginia climate producing most of their

yield in spring when soil moisture is most likely to be

available. When incorporated in a crop rotation they help

to control weeds and improve soil tilth. They help to

increase the total production per unit of land when used

in a double cropping sequence with summer crops.

Among small grains, barley (Hordeum vulgare, L.) and

wheat (Triticum aestivum, L.) have the highest yield at

soft dough stage of maturity. However, barley is ready for

harvest earlier than wheat. Nevertheless, compared to corn

(gsa maas, L.) , barley silage has a lower nutritive value

due to lower energy and higher fiber contents. These are

the main limiting factors for use in dairy rations.

The most common measures to improve the nutritive

value of the crop are to harvest in an earlier growth

stage or to raise the height of the cutting bar at harvest

to increase the grain to forage ratio.

Objectives of this study were to compare barley har-

vested at two contrastating stages of growth, boot and

soft dough, and the soft dough harvested with two cuttingheights for silage. Silages were compared in terms of:

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1. Dry matter yield and chemical composition.

2. Ensiling characteristics of the harvested materials.

3. Silage composition.

4. Silage In Vivo digestibilities.

5. Silage suitability for milk production.

6. Ruminal degradability characteristics of the silages.

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LITERATURE REVIEW

1. Introduction.

Small grains are the most common spring crops for

silage making in Virginia (Polan et al., 1968). They are

reliable and well adapted to the Virginia climate,

producing most of their yield during the spring when

adequate moisture is most likely to be available (Virginia

Cooperative Extension Service, 1983).

When small grains are incorporated into a crop

rotation, they help to improve tilth of the soil. Also they

control weeds and increase the total production per unit of

land when used in a double cropping sequence with summer

crops such as corn, sorghum (Sorghum bicolor, P.), soybeans

(Glycine ggg, L.), or other summer annuals. (Virginia

Cooperative Extension Service, 1983; Camper et al., 1972).

Edmisten (1985) reported barley and wheat tended to

yield higher than rye (Secale cereale, L.) and oats (Ayggg

sativa, L.) from boot to hard dough, and the percentage of

total dry matter in leaves was higher for barley at all

stages of maturity considered. Also barley was ready for

harvest 8 and 14 days before wheat for boot and soft dough

stages respectively.

2. Stage of Maturity and Total Dry Matter Yield. (Total dry matter yield of small grains increases as

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maturity increases (Polan et al., 1968; Boman, 1980). There

is a dramatic increase from vegetative to milk stage and

then a tendency to stabilize or to increase slightly

(Edmisten, 1985). The shattering of seeds and loss of

older leaves have been reported causes of a decline in dry

matter yield during late dough (Smith, 1960).

Polan et al. (1968) reported that the dry matter yield

of barley harvested at bloom and milk was 75.2 and 95.4%,

respectively, of that of barley harvested at dough stages

of maturity. Edmisten (1985), found the two year average

' dry matter yield of barley harvested at boot to be 52% of

barley harvested at soft dough.

3. Stage of Maturity and Composition.

Because total yield and nutritive value follow oppositetrends as maturity advances (Raymond, 1969; McCullough,

1978), it is necessary to compromise both to optimize the

yield of nutrients per unit of land. Nevertheless, contrary

to what happens with perennial grasses and legumes where

nutritive value declines rapidly with maturity, most annual

grain producing plants can maintain or even improve

nutritive value at later stages of maturity. This is due to

the increase in grain content relative to the total dry

matter accumulated (Polan, 1976).

The dry matter concentration of the material to beensiled is important because it influences the kind of

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fermentation during ensiling and as a result animal

performance (McCullough and Sisk, 1967). A dry matter

content of 30-40% is regarded as optimum for most grass

silages (Gardener and Wiggans, 1961), and dry matter

contents of 28% or higher are recommended to inhibit

undesirable clostridial fermentation (McDonald et al.,

1973).

Dry matter content of barley tends to increase with

increasing maturity, with little change prior to milk but a

rapid increase after this stage (Polan et al., 1968; Fisher

et al., 1972; Edmisten, 1985). The initial low dry matter

concentration and hence the need of wilting along with

lower dry matter yield per unit of land have been reportedas major disadvantages of harvesting barley at vegetative

stages (Polan et al., 1968; Edmisten, 1985). On the other

hand, Edmisten (1985), reported that in one of the two

years of his experiment, barley harvested at soft dough had

a dry matter content of 42.7-45.1%, considered slightly

high for optimum ensiling. DiRienzo (1987) considered the

rapid change in dry matter concentration at later stages of

maturity as a disadvantage due to the lack of flexibility

during the harvesting process.

Edmisten (1985) reported a continuous decline in "In

Vitro" dry matter digestibility (IVDMD) of barley fromvegetative to hard dough. The decline was slowest from

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vegetative to heading (77.9 to 71.8%) and a faster decline

from heading to hard dough (71.8 to 61.3%). Other

researchers reported IVDMD decreases until grain formation

begins and then stabilization (Cherney and Marten, 1982) or

even a slight increase (Belyea et al., 1978; Edwards et

al., 1968). Belyea et al. (1978) attributed the decline

recorded from vegetative to milk stages to the increase in

acid detergent fiber and the increase, thereafter, to the

increase in seed carbohydrates relative to total dry matter

accumulated.

The Van Soest detergent fiber fractionation system

(Goering and Van Soest, 1970) gives a better isolation and

a more reliable and repeatable measure of the fibrous

fraction of feedstuffs than the proximate analysis system

(Van Soest and Moore, 1965). The neutral detergent fiber

(NDF) fraction or total cell wall constituents (CWC) is

closely related to forage dry matter intake potential

(Barnes and Marten, 1979; Mertens, 1985a). Acid detergent

fiber (ADF) as well as the acid detergent lignin (ADL) have

been reported as strongly related to forage dry matter

digestibility (Van Soest and Moore , 1965), and the ADF

fraction has been frequently used to predict forage

digestibility (Van Soest and Robertson, 1980).

Edmisten (1985) and Cherney and Marten (1982) reported

that the general trend of the detergent fiber fractions in

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Ibarley was to increase with increased maturity. There is a I

sharp increase from vegetative to milk stage and a tendency ä

to stabilize or increase slightly from milk to ripe seed.

The exception is lignin which increases continuously during

the entire growth cycle. Cherney and Marten (1982) reported

values of 40.0, 29.5, and 2.4% and 53.0, 37.0 and 5.4% for

NDF, ADF and lignin at boot and heading stages of maturity,

respectively. They speculate the increase in lignin content

in stems was the major factor that accounted for the

reduction in IVDMD with increased maturity. Edmisten (1985)

reported values of 47.2, 27.9, 3.9, and 22.8% and 58.9,

34.0, 7.2, and 25.7% for NDF, ADF, lignin and cellulose at

boot and soft dough stages of growth respectively.

The data reported by Edmisten (1985) and Cherney and

Marten (1982) show at milk stage the NDF content of barley

approaches 55% and at this level voluntary intake of forage

may be negatively affected (Van Soest, 1965). On the other

hand Belyea et al. (1978) reported an increase in detergent

fiber components from vegetative to milk stage in wheat and

then a decrease at ripe seed stage of maturity due to the

diluting effect of the grain contents relative to the total

dry matter accumulated.

Polan et al. (1968) reported the crude protein

concentration of winter barley grown for forage in Virginia

declined with maturation. A similar trend was reported by

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8 ICherney and Marten (1982) for all small grain species.Theyalso

reported that the crude protein content of leaf blades

and stems declined sharply with maturity, and the crude

protein concentration of both components was reduced by onehalf from vegetative to hard dough stages of maturity.

Edmisten (1985) reported crude protein concentration

generally decreased from vegetative through milk stages.

However, from milk to hard dough it decreased slightly or

remained the same. Crude protein of 24.0, 13.4, 7.9 and

6.9% of the dry matter were reported on the pre—ensiled

barley forage at vegetative, boot, milk and soft dough

stages of maturity respectively.

As a general trend, the mineral content, particularly P

and S, tend to decrease with advancing maturity, but a wide

range within each forage species has been reported. It is

not always easy to logically relate mineral content with

stage of maturity and the average content of a certain

mineral may be of limited usefulness (Raymond, 1969).

Cherney and Marten (1982) reported that all four

species of small grains showed a decrease in macromineral

concentration with increased maturity, and only P concen-

tration dropped below 0.3% in later stages. The Ca

concentration of barley was about twice that of the other

small grains.

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14. Effect of Cutting Height.

The cutting height at harvest affects both the amount

of dry matter harvested as well as the composition of the

harvested material. The main effect of a higher cut is to

increase the proportion of heads and greener leaves and

stems in the harvested portion. Since the cell wall and, especially the lignin content is a function of age, the

harvested material would tend to have a lower content with

a higher cutting height (Sullivan, J.T., 1973).

Laissus (1968), working with timothy harvested at three

different stages of maturity and three cutting heights,

reported that the nitrogen content of the harvested part

was higher for the younger stage of growth and the highest

cut (10 cm). However, the reverse was true for the last two

more mature cuts of his experiment. This is a result of the

higher proportion of heads in the mature harvested material

and lower nitrogen content of this fraction relative to

leaves and stems (Cherney and Marten, 1982).

5. Effect of the Ensiling Process.

The word silage refers to the "material produced by the

controlled fermentation of a crop of high moisture content"

(McDonald and Whittenbury, 1973). Silage is a way to store

feedstuffs through anaerobic preservation of moist forage.

This encourages formation of sufficient concentration of

acids, especially lactic acid, to inhibit further microbial

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activity. As a result the material is preserved until

needed. The goal is for a minimal loss of nutritive value

compared to the original material (McCullough, 1978).

The ensiling process uses as a main substrate the water

soluble carbohydrates of the plant. As a result, ensiling

is a destructive process. The energy and dry matter

recovered from the silo are always less than the amount

originally stored (Edwards and McDonald, 1978).

Besides field and effluent losses chopped material has

two main losses, respiration and fermentation. The losses

caused by respiration are due to the activity of plant

enzymes and aerobic microorganisms. They usually cause

breakdown of nonstructural carbohydrate and proteins. One

of the most undesirable products of oxidation is production

of heat. Heat causes alteration of the protein fraction by

increasing unavailable protein content due to browning.

Occasionally the entire silage mass will burn (McCullough,

1978).

The amount and nature of the fermentation losses depend

on the pathway followed. Ideally the pure homolactic

fermentation pathway is the most desirable because it

causes less fermentative losses and also is the most

efficient in reducing pH because its end product is lactic

acid. McDonald et al. (1973) reported recoveries of 100.7and 92.3% for gross energy and dry matter respectively in

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well preserved silages of ryegrass, showing that the amount

of losses of well managed silages is low. Also this is the

reason many times the energy content per unit of dry matter

in well preserved silages is higher than in the original

material, although, total energy recovery is lower.

The free reducing sugars are among the most extensively

affected by the fermentation process because they are used· as substrates in the fermentation process (McDonald et al.,

1973). As a rough guide, it has been suggested that 2.5%

water soluble carbohydrates in the fresh weight of the crop

are needed to obtain a well preserved silage without

additives (Wilkins, 1981). The structural carbohydrates are

of little importance in fermentation and only hemicellulose

makes a minor contribution (McDonald et al., 1973).

McDonald and Whittenbury (1973) reported that even in

well preserved silages 50% of net protein breakdown may

take place as a result of both plant enzyme and microbial

activity but the formation of ammonia from amino acids is

caused by microbial activity. Nevertheless serine and

arginine are significantly degraded by the lactic acid

bacteria. However, the major changes in amino acids are

caused by clostridia. To prevent marked amino acid

degradation, the authors suggest a rapid pH reduction.

Reports indicate that silage in well sealed silos hasdry and organic matter digestibilities very similar to that

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in the crop before ensiling. This is true mainly because

the increase in concentration of structural carbohydrates

is compensated by a small increase in the digestibility of

the crude fiber of the silages (Wilkins, 1981).

The fermentation losses caused by the action of hetero

fermentative lactic acid bacteria will depend on the

relative proportions of glucose and fructose present in the

ensiled plant material. According to McDonald and Whitten-

bury (1973) losses of dry matter ranging 1-40% were

reported in this type of fermentation.

The most undesirable fermentation is clostridialbecause one of the end products is butyric acid. Butyric

acid is produced using lactic acid as the substrate, and

causes a reduction in silage acidity because butyric is a

much weaker acid than lactic. This allows further microbialand fungal activity usually leading to the putrefacation of

the silage, and consequently, reducing its acceptability by

the animal. The other consequence of clostridial activity

is formation of amines and the deamination of amino acids.

The increased content of ammonia not only reduces the

protein quality of the silage but also increases the buffer

capacity causing an additional reduction in acidity, and

increasing the risk of putrefacation of the ensiled

material (Edwards and McDonald, 1978).

According to McCu1lough (1978) the recommended measures

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to obtain a desirable fermentation are rapid silo filling,

a good seal to prevent air leaks, and a high density silage

well packed to assure air exclusion. The aerobic phase

should be as short as possible. Also clostridia are much

more sensitive to the dry matter content than to the pH of

the silage. It is best to have a dry matter content of 28%

or higher to prevent clostridial fermentation.

Many methods have been proposed as indexes of silage

quality. One of the oldest is the Fleig System, cited by

McCullough (1978). This system was proposed in 1938 and

based on the amounts of lactic, acetic and butyric as

percentage of total acids, assigning points according to

the proportion found in each silage. Breirem and Ulvesli,

also cited by McCullough (1978), proposed the following

values as an index of a good fermentation: pH 4.2 maximum,

lactic acid 1.5-2.5%, acetic acid 0.5-0.8%, butyric acid

less than 0.1% and ammonia—N as % of total N not exceeding

5-8%. The real importance of these indicators of silage

quality rest in the close relationship among these values

and some parameters of animal performance such as dry

matter intake. Gordon et al. (1964) reported that only

silage dry matter and lactic acid were positively corre-

lated with dry matter intake of lactating dairy cows,

whereas, butyric, propionic and acetic acid content and pH

were negatively correlated. They also reported that when a

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multiple regression analysis was applied the complete model

explained 66% of the total Variation and the reduced modelwith the variables % dry matter, % butyric and % lactic

acid in the silage explained 64% of the total Variation

found in silage dry matter intake.

6. Effect of the Diet Characteristics and Composition on

Milk Yield.

6.a.Dry Matter Intake.

There are no specific requirements for dry matter

intake (DMI), nevertheless, it is one of the most

important single factors to be considered in ration

formulation. It is recognized as the main limiting factor

in meeting the energy requirements of high producing

lactating cows (NRC, 1988). The mechanism controlling dry

matter intake in ruminants is biphasic (Forbes, 1977).

With diets of low to medium digestibility, the available

energy content and the dry matter intake are positively

correlated, but with diets high in energy the opposite is

true (Conrad et al., 1964).

Under most commercial situations, with diets of medium

or medium to low digestibility the fill capacity of the

rumen is the upper limit to intake. On the other hand with

diets with high proportion of concentrates the energy

requirement of the animal is what sets the upper limit to

dry matter intake (Conrad et al., 1964). The point at

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Zwhich feed intake changes from physical to physiological

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control is not constant and has two main controlling 1

points. The digestibility of the diet is one and the I

energetic requirement of the animal is the other (Conrad,

1966). Within the limits of physical regulation the

indigestible dry matter is the major constraint on feed

intake. According to Conrad (1966) for a certain animal

the dry matter intake of diets of different digestibility

can be predicted using the following formula: DMI= 5.4 x

W/500 x F, where DMI is dry matter intake in Kg/day, W is

the animal live weight in Kg and F is the percent of

indigestible dry matter in the diet.

There is a strong interaction between digestibility

and the level of intake. Tyrrell and Moe (1975) reported

that the rate of depression in digestibility caused by the

increase of each unit of energy intake ranges from 3.4 to

6.2% with a weighted average of 4.05%. The units of intake

are expressed as multiples of energy intake required to

support maintenance. Also, the digestibility of allI

fractions of the diet are not equally depressed. Tyrrell

and Moe (1974) reported that the depression in digestiveI

efficiency of diets containing 60% grain and 40% corn 1

silage fed to lactating and dry dairy cows was 8% for 1

cellulose and hemicellulose compared to 3% for the soluble Iresidue. I

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Another factor affecting dry matter intake is the

amount of concentrates or forage/concentrate ratio of the

diet. Under physical regulation of intake the addition of

concentrates increases dry matter intake, but there is an

interaction between the forage and concentrate fractions

of the diet. The increase in intake is not the simple sum

of forage plus the concentrate, there is always a partial

substitution of forage by concentrate. The average

substitution rate is O.43 to 0.45 units of forage per unit

of concentrate added on a dry matter basis (Ward and

Kelly, 1969). However, the substitution rate is not

constant and depends on the quality of the forage. A

forage with a digestibility similar to that of the added

concentrate can result in the substitution rate being 1 to

1. In this particular case the increase in dry matter

intake due to the addition of concentrates would be null

(Broster et al., 1981).

Another component that affects dry matter intake is

the fiber content of the diet. The general tendency is

that as fiber content increases the voluntary intake

decreases. With diets with extremely low fiber contents

intake is also depressed due to metabolic and digestive

disorders (Van Soest and Mertens, 1984).

The soluble matter in feeds occupies very little space

in the rumen and is also rapidly removed by digestion and

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passage. On the other hand the cell wall component

represents the bulky part of the diet and is the best

estimator of the requirements of volume or rumen space

(Mertens, 1980). In crude fiber (CF) and ADF extractions

only part of the fibrous components are recovered,

therefore, NDF is considered the best estimate of the

"bulkyness" of the diet. NDF is also the component of the

diet best correlated with intake (Mertens, 1980), and ADF

is better correlated to digestibility because its

lignified matrix is the most unavailable feed fraction

(Van Soest and Mertens, 1984).

Another factor of the diet affecting the potential

voluntary dry matter intake is the forage source. Sullivan

(1973) mentioned that the dry intake of silage is always

lower than the intake of hay made of the same forage. The

average reduction in intake reported by Wilkins (1981) was

33% with a range of 1 to 64%. Many products of silage

fermentation have been reported to be negatively corre-

lated with intake. Some of these are total volatile fatty

acids, acetic acid and ammonia (McCullough, 1978 and

Wilkins, 1981).

Moisture content of the diet has been mentioned as a

factor responsible for reduced dry matter intakes 1

(National Research Council, 1988). According to Chase 1

(1979) there is a relationship between the dry matter ;1

l8

content of the diet and dry matter intake. As dry matter

content decreases voluntary dry matter intake increases.

This relationship was less precise for forages containing

more than 50% dry matter and it is not clear if this

relationship is linear or curvilinear. Also most of the

articles reviewed by Chase (1979) compare diets containing

variable amounts of hays and silages and, therefore, part

of the recorded differences in intake may be accounting

for differences in intake between hays and silages rather

than in moisture content. Also dryer diets may stimulate a

greater saliva production increasing the buffering

capacity of the rumen and indirectly increasing the dry

matter intake of the diet by promoting a better and faster

digestion of the fiber fraction (Nocek, 1988).

The environment, especially the temperature and

moisture content of the air, affects the potential dry

matter intake. Ruminants are homeothermic animals that

balance the heat gained from metabolism with the heat lost

or gained from the environment. Under most normal

conditions there is a continual loss of heat from the body

of the animal to the environment and the net heat loss

depends on the heat gradient. Also the higher the air

vapor pressure the lower the vapor pressure gradient from

the skin and the respiratory tract to the air. Hence the

lower the evaporation rate and the cooling effect of

19

sweating which is the most important mechanism of heat

balance in ruminants (National Research Council, 1981).

Milk production promotes a very intensive metabolic

activity and consequently heat production. The lower

critical temperatures of -14 and -40 QC for a dry pregnant

and lactating dairy cow producing 31.1 kg of milk a day

respectively has been estimated (National Research

Council, 1981). Under heat stress conditions the

lactating cow tends to reduce feed intake to reduce the

"heat load" and the decline in intake becomes apparent at

25-27 QC with a marked decline above 30 QC. At 40 QC it is

usually no more than 60% of the intake recorded at 18-20

QC (National Research Council, 1981).

6.b.Energy Intake

There are no specific signs of energy deficiency, but

4 in lactating dairy cattle it is primarily manifested by a

decline in milk yield, loss of live weight and a depressed

reproductive performance (National Research Council,

1988). There are many expressions of energy. These are

digestible energy (DE), metabolizable enrgy (ME), net

energy for maintenance (NEM), net energy for body weight

gain (NEG), net enrgy for lactation (NEL) and total

digestible nutrients (TDN) (National Research Council,

1981). These are used to express both animal requirements

and feed value. Digestible energy only takes into account

I

1 20 1

the loss due to the energy content of the ·feces and in

many cases DE is estimated from TDN using a value of 4.409

Mcal of DE per 1 Kg of TDN (National Research Council,

1981). The major criticism to the use of TDN is that this

index is estimated at maintenance or close to maintenance

level of intake so it has to be corrected to be used with

producing animals. Secondly level of depression of

digestibility with increasing intake is not equal for all

feed components (National Research Council, 1988; Tyrrell

and Moe, 1974). Also TDN content of roughages and

concentrates is used for production purposes with

different efficiency. Therefore for milk production, 1 Kg

of TDN from a forage source is not equivalent to 1 Kg of

TDN from a concentrate source. This is due to the

differences in energy losses in heat and gases during the

ruminal fermentative phase of the digestive process (Moore

et al., 1953).

Metabolic energy takes into account energy losses in

feces and in urine. The ME requirements of lactating cows

were obtained experimentally but there is little informa-tion about the ME value of feeds. Therefore they usually

are estimated from DE. Moe and Tyrrell (1976) proposed the

following equation to estiamte ME from DE: ME = -0.45 +

1.10*DE, where ME and DE are expressed as Mcal/Kg of drymatter in the feed.

21 .

«

As a way to minimize the bias introduced by the use of

TDN, DE or ME, net energy has been proposed as a system ?which takes into account digestive losses as well as

differences in nutritive value due to differences in level

of intake. The efficiency of utilization of NE of a feed

depends on whether it is used for maintenanace, growth,

milk production or fattening (Lofgreen and Garrett, 1968,

Moe et al., 1972) and for this reason each feed usually

has more than one NE value. These are NEM for net energy

of the feed for maintenance, NEG for weight gain, and NEL

for milk production. Lactating animals use feed NE with

the same efficiency for maintenance as for milk produc-

tion. Therefore a single NE value is required to estimate

energy requirements (Moe et al., 1972).

The requirements for milk production varies with

amount produced and fat content. The National Research

Council (1988) estimates this value as 0.74 Mcal NE/Kg for _

milk containing 4 % milk fat, but the equation is:

NEL (Mcal/Kg Milk)= 0.3512 + (0.0962*(% Fat))

Maintenance requirements depends on cow size and

activity of the cow. Moe et al. (1972) estimated the

maintenance requirements of lactating dairy cows as 73

Kcal of NE/Kg°·’5 of live weight and the National Research

Council (1988) estimates it as 80 Kcal/Kg°·’5 of live

weight allowing a 10% increase in maintenance to compen-

l

22sate

for activity. Also the NE requirements for pregnancy

increase exponentially with a marked increase during the

last 4 to 8 weeks of gestation (dry period). It has being

estimated as 30% of the maintenance requirements (Moe and

Tyrrell, 1972). According to Moe et al. (1972) an

additional 3 to 6 Mcal NE per day would be required to

meet these requirements.

In general DE, TDN and ME content of feeds was

obtained at maintenance levels of intake, but most of the

values of NE were obtained at higher levels (National

Research Council, 1988). Other values were estimated

according to the equation of Moe and Tyrrell (1976) which

uses the TDN value of the feed corrected by intake level.

The equation is as follows: NEL= 0.0245*TDN - 0.12, where

NEL is expressed in Mcal NE/Kg of dry matter and TDN as %

I of the dry matter.C

Another source of energy especially important during

the early lactation period is body weight loss. This is

estimated as 6 Mcal NEL/Kg body tissue and used with an

estimated efficiency of 82% for milk production (Moe et

al., 1971).

6.c.Protein Intake.

Protein is a vital nutrient required for maintenance,

reproduction, growth and lactation of dairy cattle and the

requirements for protein by ruminant animals are second in

123 l

quantity only to energy (Agricultural Reaserch Council,

1980). Ruminants can use many different sources of

nitrogen to meet protein requirements, but the tissue

requirements of ruminants as well as other animals are for

amino acids absorbed from the small intestine. Neverthe—less, their major ecological advantage is that true

protein can be synthesized from nonprotein nitrogen and

carbon skeletons by the ruminal microflora (Van Soest,

1982). Virtanen (1966) reported productions of 4000 kg of

milk per lactation using protein free diets, but the level

of production depends on the microbial flow from the rumen

(National Research Council, 1985). Under highly demanding

situations like fast growing animals or high yielding

lactating cows the microbial protein flow to the small

intestine may not be enough to satisfy the requirements of

the animal. Therefore, dietary protein escaping rumen

degradation is needed (Huber and Kung, 1981).

There are many nitrogen sources available in ruminant

diets. Some of these are proteins and peptides, free

amino acids and nonprotein compounds. Nonprotein compounds

include free ammonia, nucleic acids, urea, nitrates,Maillard products and some other nitrogen containing

compounds (Van Soest and Sniffen, 1984).

Feed nitrogen can be classified into three groups with

different biological significance: soluble nonprotein

( 24

nitrogen (NPN), true protein and unavailable protein.

Another classification is fraction A (soluble), BJ(available) and C (bound), respectively (Pichard and VanJ

Soest, 1978). From the point of view of ruminal avail- J

ability, the A fraction contains mostly NPN and rapidly

degradable protein, the B fraction is mainly true protein

that is degraded in the rumen at a measurable rate, and

the C fraction is unavailable. The C fraction is mainly

composed of Maillard products, lignified nitrogen and

tannin—protein condensates, which are very slowly or not

degraded at all in the rumen (Satter, 1986).

Rumen available feed nitrogen can be changed in the

rumen through proteolysis, deamination and microbial

protein synthesis (Tamminga, 1979). The extent to which

dietary protein can be altered in the rumen and used for

microbial protein synthesis is variable and a range from' 40 to 80% has been mentioned (Satter and Rofler, 1975).

The primary determinant of the amount of protein

synthesized in the rumen is the amount of energy available

for microbial growth. Chalupa and Ferguson (1988) reported

that the bacterial and protozoal crude protein flow can be

predicted with an accuracy of 77% if the daily NEL intakeis known. The other potentially limiting factor is the

availability of nitrogen. Dietary crude protein contentslower than 9% have been reported as limiting for fiber

J

25 1

digestion due to impaired microbial growth (Van Soest,

1982).

The potential degradability of a protein in the rumen

depends on microbial proteolytic activity, microbial

access to the protein, protein structure, rumen retention

time, rumen turnover and chemical and physical treatment

of feeds (National Research Council, 1985). Therefore,

protein degradability of a certain feedstuff will vary

with circumstances unique to its use.

The National Research Council (1988) uses two systems

to express protein content of feeds and requirements of

the animal. These are crude protein system and the rumen

degradable and undegradable systems. Crude protein (CP) is

the oldest method of expressing protein requirements, and

assumes all feed nitrogen is protein and this protein has

a nitrogen content of 16%. The main disadvantage is it

does not differenciate between nonprotein and true protein

nitrogen. Also it does not differenciate between ruminally

degradable and undegradable protein, but the analysis is

easy to perform, highly repeatable and most of the

experimental data uses CP as the unit to express the

protein requirements of ruminants. Also there is a strong

relationship between the protein content of the diet and

animal response (Van Horn, 1982). The new National

Research Council (1988) system establishes requirements

1 261 1

for rumen undegraded intake protein (UIP) and degraded

intake protein (DIP). This system takes into accountsimultaneously the crude protein requirements of the

ruminal microbes and the host animal. Measuring the

undegraded protein content of a feedstuff requires the

measurment of the total protein flow to the intestine and

the separation of the protein of dietary origin from the

proteins of bacterial, protozoal and endogenous origin. In

vivo estimates (sampling of abomasum or duodenum content),

in situ (ruminal incubation of feeds in dacron bags) and

in vitro techniques (laboratory procedures) have been used

to evaluate feed proteins, but the experimental data is

still limited and based on very few observations of each

feedstuff (National Research Council, 1988).

The in vivo method to estimate ruminal degradability

of proteins is expensive and labor—intensive, and requires

the use of surgically prepared animals with cannula in the

abomasum or proximal duodenum. The method is not perfect

and the main sources of error are the measurment of rumen 2turnover and the difficulty in estimating protein from

protozoal and endogenous origin. Nevertheless, it remains

the reference method (Stern and Satter, 1982).‘

The main advantge of in vitro methods is they are

cheaper than in vivo methods and they do not require

cannulated animals or sophisticated laboratory equipment.

27

Results are obtained in a relatively short period and they

allow the testing of large numbers of samples. Also the

use of enzymes eliminates the problem of microbial

nitrogen contamination due to microbial attachment to

fiber particles when analyzing forage proteins (Poos—Floyd

et al., 1985).

Enzymes of different origin (bacterial, plant and

fungal proteases) have been used to estimate rumen escape

nitrogen. Poos-Floyd et al. (1985) found the enzyme assay

more closely related to in vivo protein escape than any of

the five solubility techniques evaluated. Nocek et al.

(1983) conclude that the protease from Streptomyces

griseus could be used to determine the amount of protein

escaping degradation in the rumen.

Other in vitro methods involve separation of true

proteins soluble in neutral and acid detergent solutions

(Pichard and Van Soest, 1978). The main advantage is the

method can be easily adapted by most analytical laborator-

ies. One N fraction is buffer insoluble but soluble in Äneutral detergent solution. This fraction is a constitu-

ent of the cell solubles and would have a fast rate of

digestion (subfraction B1). The protein insoluble in

neutral but soluble in acid detergent is considered as

completely available but digested at a slower rate (B2)

than the previous fraction. The nitrogen insoluble in acid I

L

28 ;

detergent is considered unavailable and represents the C

fraction (Pichard and Van Soest, 1978).

Another in vitro method used to estimate protein

degradability is protein soluble in certain solutions.

Many solvents including water, autoclaved rumen fluid,

mineral buffers simulating saliva or rumen fluid and salt

solutions have been used, but at present there is no bestmethod for this determination (Krishnamoorthy et al.,

1982). The in vitro solubility of a protein is affected by

many factors such as agitation, lenght of extraction time,

temperature, pH, ionic strenght,etc. (Waldo and Goering,

1979). Also protein structure affects solubility. Albumins

and globulins are more soluble than prolamines and

glutelins and the former include NPN and the latter bound

nitrogen in their estimations respectively (Who1t et al.,, 1973). Another shortcoming of this method is soluble

protein tends to be rapidly degraded but insoluble protein

is not synonomus with undegradability. On the other hand,

Satter et al. (1977) reported that the regression of g

solubility and degradability is 0.54 indicating that

solubility can explain approximately one half of the

variation found in ruminal degradability.

Estimation of protein degradability in the rumen using

the in situ method is an alternative technique thatprovides rapid and reliable estimates for a relatively

l

29

large number of samples and a wide Variety of feedstuffs. 1An advantage of this technique compared to laboratory 1

methods is the feedstuffs are subject to the digestion 1

processes that occur in the rumen (Orskov et al., 1981).

The method is based in the suspension of dacron bags

containing the feedstuffs to be tested in the rumen for

different periods of time. After the incubation the

residues are analyzed for chemical components and thedissapearance from the bag are regressed on time of

incubation and the dissapearance rate per unit of time is

determined (Broderick, 1982).

There are a number of factors in this technique that

may affect the results, leading to erroneus interpretation

of the data. Among these factors are the bag pore size,

sample weight to bag surface area ratio, sample particle

size, presoaking, bag introduction sequence into the

rumen, cow and time Variation, cow diet and bacterial

nitrogen contamination are the most relevant (Nocek,

1985). ;1

Nocek (1985) concluded based on in situ soybean meal

incubation that:

1. The ruminal introduction of bags in reversal order

(72 h first, 1 h last) decreased Variation of in 1

situ digestion profiles. 12. Use of standard ingredients detected time related 1

30 I

I

variation.

3. Bacterial N contamination did not affect N

digestion rate constant.

4. The dissapearance of soluble dry matter and N

during presoaking is affected by sample particle

size and sample weight to bag surface area ratio

and bag pore size.

5. Sample particle size of 1, 2, or 5 mm or unground

had no influence on DM or N digestion.

6. Sample weight to bag surface area ratio of 12.6

mg/cmz compared most favorably with literature in

vivo estimates for ruminal N digestion.

7. Bag pore sizes from 40 to 102 microns were similar

and higher in estimated ruminal protein availabil-

ity than smaller pore sizes, and compared favorably· with in vivo literature estimates.

In both methods in vitro and in situ, the degradation

of protein has been described as a function of time of

incubation and only fraction B is considered to be ;

affected by relative rates of passage and degradation.

This potentially degradable fraction has been described by

first order (linear model) kinetic rate constants, and a Yprimary assumption of the first-order kinetic model is the „

pool is homogeneous and degraded as a linear function of I

time in the rumen. These assumptions are violated when theÄ

31

soluble (A) and the nondegradable (C) fractions are not

determined and substracted from the fermentation sequenceor when an heterogeneous mixture of potentially degradable

fractions is present and is degraded simultaneously at

different rates (Nocek and English, 1986).

A monoexponential rate of decay describes the

degradation of fraction B and estimates its value at 0

time. The degradation constant K6 is obtained by

regressing the natural logarithm (Ln) of the percent of

sample remaining in the bag minus the C fraction over

time. In this way the intercept and the slope of the

resulting stright line represent the content of the B

fraction in the original sample (B at time 0) and the

degradation constant (K6) respectively (Zerbini, 1984).

7. Effect of the diet on milk composition.

In general the fatty acids in milk are 50% derived

from synthesis within the mammary gland and 50% from

dietary origin. The short chain fatty acids resulting from

the rumen fermentation (C1 - C12) are almost entirely

synthesized in the mammary gland from acetate and

beta-hydroxybutyrate , whereas long chain fatty acids (C16

or greater) are almost exclusively of dietary origin.

Intermediate length fatty acids (C12 - C16) are from both

sources (Linn and Otterby, 1988).

The amount and physical and chemical characteristic ofLLL _ _ _.

32 L1

dietary carbohydrates affect both fat and protein content

of milk. Carbohydrates account for 60 — 80% of the dry

matter of the diet of a dairy cow. Carbohydrates are

present as structural material (cellulose, hemicellusose,

etc.), plant reserve products (starch, fructosans, etc.)

and as simple sugars. Carbohydrates are the primary source

of energy of the rumen microbes and the variation in their

composition or quantity affects the composition of the

microbial population and as a result the end products of

rumen fermentation (Rook, 1976).

Milk fat percentage is positively related to rumen

molar percentages of acetic and butyric acids and

negatively to propionic acid. The typical composition

(molar percentages) of short chain fatty acids in rumen

liquor of cattle in a high fiber diet is 60 — 70% acetic,

17 - 20% propionic and 7 — 12% butyric acid. A progressive

substitution of roughages by starchy concentrates is

followed by a fall in acetate and an increase in propionic

concentration. This change is a result of a switch in

microbial population (Rook, 1976).

Feeding readily fermentable carbohydrates depresses

fiber digestion, rumen pH, and production of acetic and

butyric but promotes production of propionic acid in the

rumen. Increased propionic acid promotes an increased

glucose formation in the liver and consequently an

33 1I

increase in insulin production. This increased insulin

level reduces the availability of body fatty acids for

milk fat synthesis which along with a reduced supply of

acetic and butyric acids from the rumen may cause a

depression in milk fat content (Linn and Otterby, 1988).

It has been reported that a rumen molar percentage

higher than 25% of total volatile fatty acids from

propionate is needed before there is a significant

negative relationship with milk fat. Also a linear

increase in milk fat percentage occurs as the ace-

tate/propionate ratio increases up to 2.2, above this

level little change in milk fat has been found (Linn and

Otterby, 1988).

The critical forage/concentrate ratio appears to be

40/60 in a dry matter basis, beyond which additional

concentrate drastically lowers milk fat content. Also at

high levels of intake more forage is needed in the diet

than at lower levels of intake to maintain normal milk fat

percentages. Finely ground forages result in higher levels

of propionate during the fermentation in the rumen,

lowering milk fat content. Woodford et al. (1986) reported

that a mean particle size of 0.64 cm or greater is

required to keep the molar percentage of propionate below

25% and a milk fat content of 3.6% or above.

Mertens (1985a) recommended a minimum of 28% NDF or a

34

daily amount equivalent to 1.2% of body weight. This

relates to about 18% ADF in diets of lactating cows in

order to maximize milk and fat yield. Stage of maturity is

important because it effects fiber content of the forage.

Also carbohydrate source can influence rumen fermentation

and as a result milk fat content. Sutton (1985) reported

the lower ruminal degradability of corn compared to barley

would result in production of milk with a higher fat test.

The effect of dietary crude protein is to affect milk

yield and as a result milk protein yield, but only a small

effect on milk protein percentage (Linn and Otterby,

1988). Insufficient amounts of dietary protein will

reduce milk protein concentration. This effect in

minimized when protein of low ruminal degradability is

fed, but an increase of dietary crude protein supply has

, little effect on milk protein percentage (Linn and

Otterby, 1988).

The total amount of energy consumed, the energy

density of the diet and the source of dietary energy all

have been reported to affect the protein content of milk.

Cragle et al. (1986) in a review of 36 experiments

reported that cows consuming diets with 59% concentrates

produced more milk, milk protein, fat and lactose than

cows on diets containing 49% concentrates. The increase in

milk protein was 85% attributable to an increased milk

L

35 )

yield and only 15% to increased milk protein percentage.

The increased production of propionic acid in the rumen

induced by the feeding of higer proportions of concen-

trates or reducing forage particle size increases milk

protein content, but the exact mechanisms are unknown

(Rook, 1976).

It is very difficult to change the lactose content of

milk because it is the main osmotically active constituent

and is the main determinant of milk yield. Lactose

percentage is not increased by high concentrate feeding.

Severe malnutrition or underfeeding of energy in early or

late lactation or protein in early lactation can decrease

lactose percentage (Linn and Otterby, 1988).

MATERIALS AND METHODS

1. Field Trial.

At the Virginia Tech Dairy Center, three fields of 5.6

(PT), 3.8 (HB) and 7.6 (Wt) hectares and having soils of

the groups Duffield-Ernest Complex, Guernsey silt loam and

Groseclose and Poplimento Soils, respectively, were planted

with Maury barley. They were seeded using a planter (3.20 m

width) with a distance between rows of 17.8 cm.

Fertilization was according to soil analysis (Table 1).

The second nitrogen fertilization in spring consisted of 58

kg/ha of N to each field on April 24.

On April the lst, at Zadocks' Growing Stage 30 (1974),

plant tissue samples were collected from each of the three

fields and analyzed for macro and micro mineral content (A

& L Agricultural Laboratory). Results are presented in

Table Al of the Appendix.

Rainfall and average daily temperature recorded during

the growing season of the crop is presented in Table All of

the Appendix.

According to slope, each field was divided into two

blocks of approximately the same area, after which areas

corresponding to each treatment were randomly assigned.

Field treatments were whole barley plant harvested at (

364

X

X

“ 37

ITable 1. Planting date, seeding rate (kg/ha) and

fertilization date and rate of the barleyfields used in the experiment.

kg/ha

Field Date Seeded Seeding Rate Fert.Date”ü””—E——”E—

PT 10/08/87 92 9/10/87 7 19 19HB 10/09/87 92 9/10/87 29 39 39Wt 10/08/87 92 9/10/87 29 39 39

bwaSharvested at two heights. Stages of maturity were deter-

mined according to the Zadocks’ Code (1974) for the deter-

mination of growth stages in cereals.

Boot stage was cut with a 2.74 m width mower and wilted

2 d before ensiling. Soft dough treatments were direct cut

with a cutter bar 3.66 m width and immediately ensiled.

Table 2 summarizes the main characteristics of the

harvested materials.

To estimate yield, material harvested from estimated

average areas of approximately 1009, 1097 and 1485 square

meters for boot, SD-Lo and SD—Hi, respectively, was loaded

into previously tared wagons and reweighed to estimate

total plant yield. Each treatment within blocks was

sampled two times using the above procedure. Each wagon was

sampled in ten different places and depths and a sample of

approximately 2 kg was taken. One half was stored in the

freezer at -28 QC and the other half was sent to the VPI

I

38I

Table 2. Growth stage, cutting height (cm) , theoreticallenght of cut (cm) and date of harvest of thetreatments.

Growth Cutting Chop Date of Treatment Stage.Height Lenght Harvest

(Cm) (Cm)

Boot Boot Stage 15 0.48 5/07/88SD—Lo Soft Dough 15 0.64 6/06/88SD-Hi Soft Dough 25 0.64 6/07/88

twosamples were taken from each treatment in each block and

stored in the freezer.

For laboratory analysis a composite subsample of the two

samples from each treatment in each block was dryed at 659

C in a forced air laboratory oven until constant weight was

obtained and then ground to a particle size of 1 mm with a

Wiley Mill. The laboratory analysis of the prepared sample

included dry matter and total nitrogen content determined

by the Kjeldahl method modified by trapping ammonia in 4%

(wt/vol) boric acid solution and titration with 0.1 N HC1

(Association of Official Analytical Chemists, 1980).

Neutral detergent fiber (NDF), acid detrgent fiber (ADF),

cellulose and lignin were determined according to the

procedures described by Goering and Van Soest (1970).

Hemicellulose was determined as the difference between NDF

and ADF. The modified NDF procedure described by Mertens

(1985b) was used with all samples. To determine total water

II

1 39 I

I

soluble nitrogen 20 g of fresh sample were thawed and

homogenized with 100 ml of distilled water for 2 min in a

commercial blender, then filtered through 4 layers of

cheese cloth and the filtrate centrifugated at 27,000 g for

20 min. Total nitrogen was determined on the supernatant by

Kjeldahl as described above. True protein in the superna-

tant was precipitated using a solution of 50% (wt/vol)

tricholoacetic acid (TCA), until a concentration of 10% of

TCA in the sample was obtained. Then the sample was centri-

fugated again at 27,000 g for 20 minutes and total nitrogen

determined in the supernatant. Water soluble true protein

was estimated by difference. Soluble sugars were estimated

by the procedure described by Davis (1976).

Analytical procedures were conducted in duplicate and

repeated when disagreement between duplicates were greater

than 5%. A completely randomized block statistical design

was applied for the analysis of the data, with 3 treatments

and 6 blocks. The Duncan’s Multiple Range Test was the

means separation test used.

To analyze the yield and composition of the harvested

material the following statistical model was applied:

Y15=}J.+<!1 +ß5 +815

where:

Y:;0bserved Value of Treatment i in Block j for

yield and composition of the harvested mate-

40

Nrial.

u Population Mean

al Treatment Effect (i= 1-3)

B; Block Effect (j= 1-6)

s1;Random Error associated to the observed value

of treatment i in the block j.

Table A6 of the Appendix presents a typical analysis of

variance table for this trial.

2. Silage Evaluation.

Harvested material was ensiled in three stave silos of 3

m diameter and 12 m height. Because field yields were much

greater than silo capacities only part of the harvested

material was ensiled. Silo 1 contained material harvested

at boot stage (boot) and was composed 39% of wet material

from HB and 61% from PT fields. Silo 2 contained material

harvested at soft dough at 15 cm above ground (SD—Lo) and

was 90% filled with material from the PT field and 10% from

WT. Silo 3 contained material from the treatment SD—Hi, and

89% of the material came from PT and 11% from WT fields

respectively.

Each silo was filled in the same day of the harvest and

a partial wagon load was blown into the silos the next

morning after material settled. Then silos were sealed with

a layer of ultra violet nylon until opened on July 11th,

1988. After opening spoiled top material of each silo was

41 I

unloaded, weighed and sampled to determine composition.

During the feeding period, silages were sampled once a

week and stored in the freezer at -289 C for chemical

analysis. For analytical purposes silage samples were

composited by two week periods, except the first period

that was composed of 3 weeks.

Silages were dried in a forced air laboratory oven at

659 C and then ground with a Wiley Mill fitted with a 1-mm

screen. Laboratory analysis of the silages included DM

determination as described above, total nitrogen by the

Kjeldahl method as previously described and expressed as

crude protein (CP = N x 6.25), total water soluble nitrogen

and total water soluble true protein as described, and

insoluble nitrogen in a borate phosphate buffer (BUFFIN-4

SOL-N) as described by Krishnamoorthy et al. (1982).

Neutral (NDIN) and acid (ADIN) detergent insoluble nitrogen

were determined using filter paper (Whatman 541, 12.5 cm)

instead of crucibles to collect the residue. NDIN and ADIN

were determined by Kjeldahl on both filter paper and

residue and then corrected by nitrogen content of the

filter paper. Neutral detergent fiber (NDF), acid detergent

fiber (ADF), cellulose and lignin were determined according

to the procedures of Goering and Van Soest (1970), and

hemicellulose was determined by difference between NDF and

ADF. Phosphorus, potassium, calcium, magnesium, sodium and

4211

sulphur (P, K, Ca, Mg, Na and S) were determined following

nitric and perchloric acid wet digestion (Association of

Official Analytical Chemists, 1980), and reading the

mineral concentration in an Inductively Coupled Plasma(ICP) Spectrometer (Soil Testing and Plant Analysis Labora-

tory of VPI). Silage pH was determined according to the

extraction and analytical procedure described by Barker and

Summerson (1941). Lactic acid content was determined by

colorimetry according to the procedure described by Barker

and Summerson (1941) and modified by Pennington and Suther-

land (1956). Acetic, propionic and butyric acids were

determined using a Vista 6000 (Varian Associates, Inc.) gas

chromatograph fitted with a hydrogen flame ionization

detector, and maintained at 1759 C. Approximately 2 ul of

silage extract were injected into the column (the glass

column, 1.8 m x 2 mm internal diameter, packed with 10% SP

1200, 1% H¤PO4 on 80/100 Chromabsorb W.AW.), held at 1259

C. Temperature of the injection site was held at 1809 C,

and nitrogen was used as carrier gas (4 ml/min).

All the analytical procedures were run in duplicates and

repeated when disagreement between replicates was greater

than 5%. To analyze silage data a completely randomized

statistical design was applied. The Duncan's Multiple Range

Test was used to compare means.

To analyze silage composition the following statistical

1

43

Lmodel was applied: ’

Yi;=u+a:+si;

where:

Yi; Observed value of treatment i, period j

u Population mean

ai Effect of treatment i (i=l—3)

si; Random error associated to the observation of

treatment i in period j

Table A7 of the Appendix presents a typical analysis of

variance table for this data.

3. Heifer Digestibility Trial.

An In Vivo digestibility trail was conducted between

August 8 and 20, 1988. For this trial 12 Holstein heifers

weighting 291 +/— 17 kg and with an average age of 11.1

+/-0.4 months were blocked according to body weight and

randomly assigned to one of the 3 silages. Heifers were

housed in individual stalls with concrete floor. Between

8/03/88 and 8/08/88 heifers were introduced to a general

pre-experimental diet of barley silage harvested at soft

dough stage plus 57 g/heifer/d of mineral supplement top

dressed on the silage. Composition of this silage is

described in Appendix Table A5 and the composition of the

mineral supplement is described in Table A4. During the

pre-experimental, adaptation and collection periods heifers

44N

I

were individually fed using wooden boxes fitted to the

stalls. They were fed once daily at 1130. Feed refusalswere swept, weighed and the weight recorded daily at 1100.

The adaptation period lasted 6 d (from 8/O9/88 to 8/15/88).

During this period heifers were fed in excess of their

appetite and voluntary intake of each heifer was recorded.

The collection period lasted from 8/16/88 to 8/20/88 and

from 8/13/88 the amount of feed offered was 90% of the

voluntary intake recorded during the adaptation period.

During the collection period all the feces were manually

collected and to avoid urine contamination the concrete

floor was washed with water using a high pressure hose

after urination. This required 24 h/d monitoring for the 5

d collection period.

Approximately 0.5 kg of each of the silages fed were

sampled each day of the collection period from the carts

before feeding and stored in the freezer for later analy-

sis. Feces from each heifer were collected in previously

tared containers. The weight of the feces was recorded

daily at 1200 and an aliquot equivalent to 2% of the

recorded weight was taken and stored at 4Q C until the end

of the collection period. At the end of the collection

period the 5 feed samples/heifer were composited by silo

and the 5 fecal samples were composited by heifer.

Silages and fecal samples were analyzed for total

I

45

J

nitrogen by the Kjeldahl method modified by trapping

ammonia in a 4% (wt/vol) boric acid solution and titration

with 0.lN HC1. To minimize loss of volatile nitrogenous

compounds the total nitrogen determination was done on the

fresh materials. The frozen silages were ground in a Wiley

Mill fitted with a 5 mm screen using dry ice, then mixed,

subsampled, thawed and analyzed. Feces were digested along

with filter paper (Whatman 541, 12.5 cm diameter) and the

nitrogen content of the feces determined by substracting

the nitrogen content of the filter paper.

For the remaining analytical procedures, silages and

fecal samples were dried at 659 C in a laboratory forced

air drying oven and ground in a Wiley Mill fitted with a 1

mm screen. Dry matter was determined as described. Ether

extract (EE) was meassured using petroleum ether as the

extraction solvent. The sample was washed 1 h and rinsed 2

h in a Soxtec System HT apparatus (Tecator). The EE content

was determined by weight difference before and after

extraction in previously tared extraction cups. Acid

detergent fiber (ADF) and neutral detergent fiber (NDF)

were determined according to the method described by

Goering and Van Soest (1970). The inorganic content was

determined by ashing samples of silages and feces in a

laboratory muffle furnace at 6029 C for 3 hr. Organic

matter was calculated as the difference between dry matter

46

and ash content of each sample. The content of nitrogen

free extract was calculated as the difference between dry

matter and the remainder of the proximate components. The

procedures described by Schneider and Flatt (1975) were

used to calculate the digestibility of the different

fractions.

The acid detergent fiber content was used to estimate

crude fiber, according to the following equation:

ADF%= (Crude Fiber / 0.75) - 3.56 by Martin (1980).

The calculation procedure to estimate total digestible

nutrients (TDN) was the one described by Schneider and

Flatt (1975).

The statistical procedure to analyze the digestibility

data was a completely randomized block design with 3

treatments and 4 blocks. To analize the digestibility

coeficients of the proximate fractions and the TDN content

of the treatments the following statistical model was used:

Ylj =}.1+<!1+ßj +815

where:

Yij Observed value of treatment i in block j

u Population mean

dx Effect of tretment i (i=l-3, silages)

Bj Effect of block j (j=l—4, heifers)

sjj Random error effect on the ijth observation

A typical analysis of variance table for the evaluation

47

of the digestibility data is presented in Table A8 in the

Appendix.

4. Lactating Cow Feeding Trial.

Thirty six lactating Holstein cows, 18 primiparous, and

18 with an average lactation number of 3.4 +/— 1.9, an

average milk production of 32 +/— 5 kg/d, 72 +/- 40 days in

milk and a body weight (BW) of 567 +/- 62 kg, were blocked

according to milk production, days in milk and lactation

number and assigned to one of six experimental diets. A

pre—experimental diet containing barley silage harvested at

soft dough and 15 cm cutting height was fed to all cows for

17 d (from 6/27/88 to 7/13/88). Composition of this diet is

described in Table A2 in the Appendix. The feeding trial

lasted 60 d (from 7/13/88 to 9/11/88). Experimental diets

were formulated to be isonitrogenous with a CP content of

16% on DM basis. Each diet was the combination of one of

the three treatments of barley silage and two forage /

concentrate ratios on a DM basis (75/25 or 60/40) (Table

3).

The concentrate ingredients were soybean meal, dry

shelled corn and a commercial mineral supplement. The

composition of the concentrates and the mineral mix is

presented in Appendix Table A3.

Silages were removed from silos two times daily, at 1100

and 1400 and the diets mixed twice daily (1200 and 0500).

48 11

Table 3. Experimental diet composition in terms of barleysilage source and forage/concentrate ratios (drymatter basis).

75/25 A C E

60/40 B D F

Cows were kept in individual stalls and individually fed at

0630 and 1300, with permanent access to fresh drinking

water. Cows were out of the barn for milking and excercise

between 0900 and 1330 during the day and between 2330 and

0030 at night.

Barley silages and total mixed diets were sampled weekly

and sent to the Forage Testing Laboratory of VPI for

analysis of nutrient composition. Diets were readjusted

weekly for crude protein content.

Milk production was measured at each milking. Samples

were taken on consecutive days every two weeks and the two

milkings of each day were composited in proportional

Volumes. Composite samples were sent to the DHIA Laboratory

at VPI to be analyzed for fat, protein, lactose, solids non

fat, total solids and somatic cell counts. Milk components

were determined with a Mark I Multispec by infrared absor-

bance and somatic cell counts were determined in a 180

Fossomatic Ultraviolet spectrophotometer.

Cows were weighed every 2 weeks. Feed refusals were

11

49 ‘

WW

weighed four times a week (Tuestday to Friday) at 0900

after the cows were taken out of the barn. Intake was

calculated as the difference between amount offered daily

and amount rejected.

In this experiment there were 6 treatments (diets) and 6

blocks. The statistical model to analyze milk production,

milk components, dry matter intake and body weight change

was the following:

Ys.5=}J.+¤1+ß5+£15

where:

Yi; = Observed value of treatment i and block j

ai = Effect of treatment i (i=A to F)

B; = Effect of block j (j=1-6)

si; = Effect of random error on ijth observation

A typical analysis of variance table used for milk

production, milk components, dry matter intake and body

weight change is presented in Table A9 in the Appendix.

Average daily milk production and milk components of the

pre—experimental period were used as covariates for analy-

sis. To test the interaction, silage source x forage /concentrate ratio a model containing 3 silage treatments, 6

blocks and 2 concentrate levels was used, an example of

this analysis of variance table is presented in Table A10

in the Appendix.

50

In all cases the mean separation procedure used was the

Duncan’s Multiple Range Test.

To estimate the relationship among the variables DM,

TDN, ADF, milk yield, 4% fat corrected milk yield, milk

fat, dry matter intake, intake of TDN, intake of ADF, and

body weight change associated with the experimental diets,

the correlation coefficients between these variables were

calculated based on one observation per cow (n=36).

5. Ruminal Deqradability Study.

The In Situ bag technique was used to determine the

ruminal degradability of dry matter, nitrogen compounds and

acid detergent and neutral detergent fiber fractions of the

three silages. Also concentrate ingredients and the six

total mixed rations used in the feeding trial were analyzed

and degradabilities determined.

Two ruminally fistulated cows producing an average of 34

kg of milk per day were used to incubate the feedstuffs.

Cows were fed a barley silage based diet for 10 days before

incubations were started. Composition of the diets of these

two cows is described in the Appendix Table A2 and is the

same as that fed in the lactating cow feeding trial.

The bags (10 x 20 cm) for incubation were made of spun

polyester, with a pore size of 59 microns. Between 5 and

10.5 g of feedstuff were placed in each bag giving a sample

weight to bag surface area ratio of 12.5 to 26.3 mg/cmz

51

(Nocek, 1985). Due to the large number of feedstuffs to

test, samples were grouped and incubated in two separate

runs. On 9/21/88 at 1900 the silages (boot, SD—Lo and

SD-Hi) and the concentrates (soybean meal and shelled

corn), were tested. On the second run on 9/28/88 at 1900

the experimental diets A to F were incubated.

Bags were removed at 0, 2, 12, 24 and 72 h respectively.

Two bags were used for 0 and 2 h, three for 12 and 24 h and

four bags for 72 h, for a total of 14 bags per feedstuff

tested and a maximum of 72 simultaneous bags per cow. Bags

were tied to a chain attached to the fistula lid according

to incubation time. Before placement in the rumen, bags

were soaked in warm (309 C) tap water for 15 min to remove

water soluble material and to reduce lag time for wetting

in the rumen. Bags were physically pushed into the rumen

and placed into the ventral sac in reverse order, beginning

with the 72 h group at 1900 h. All were removed at once at

the end of the 72 h period (Nocek, 1985). Immediately after

removal bags were placed in an ice bath to stop or minimize

bacterial activity and then rinsed overnight until rinse

water was clear. Bags were then individually rinsed by

hand, opened and placed in a forced air oven at 659 C until

constant weight was reached. Bags with the dried residue

were weighed to estimate DM disappearance. Bag residues

were composited according to feedstuff and incubation time

52

and ground to a particle size of 1 mm in a Cyclone mill.

Laboratory analysis of the incubated residues includednitrogen content by the Kjeldahl method as previously

described, and acid detergent and neutral detergent fiber

by the Goering and Van Soest (1970) method.

Nitrogen, ADF and NDF were corrected by DM disapperance

in each incubation time to estimate the ruminal degradation

of the fractions. The ADF and NDF content of the 72 h

incubation time of soybean meal and shelled corn was not

estimated because of the small amount of residue.

The degradability of the dry matter, nitrogen compounds,

ADF and NDF fractions of the feedstuffs was calculated

according to the procedures described by Zerbini (1984).

Only fraction B was considered to be affected by relative

rates of passage and degradation at any time. To describe

the degradation of fraction B and to estimate its value at

time 0 a monoexponential rate of decay was used. The

degradation constants kd were calculated regressing the

natural logarithm (Ln) of the per cent of residue remaining

minus the residue in the C fraction (residue at 72 hours)

over time. Intercept and slope of this regression line

represented the value of the B fraction in the original non

incubated sample and its degradation constant rate (kd)

respectively.

The B fraction is calculated by the following equation:

53 '1

B = E-intercept

where: e = 2.71828 'Knowing the amount (dry matter, nitrogen, ADF or NDF) in

fraction C and fraction B at 0 time, the content in frac-tion A can be calculated as follows:

A = 100 - (B + C)

The feedstuff fraction remaining in the bag at any time

can be calculated as follows:Fraction remaining = B x

e‘“° + C for any t>0

so (Fraction remaining - C) = B xe‘“°

or Ln(Fraction remaining - C) = Ln B - kt

where:

Ln B = intercept (regression line)

k = slope (regression analysis)

t = any point in time (hours)

C = residual at 72 hours,(or 24 for NDF and

.ADF of soybean meal and corn)

After determinig the fraction content (per cent of dry

matter, nitrogen, ADF or NDF) in fractions A, B and C the

fraction degradability (D) in per cent can be calculated

using the equation of Orskov and McDonald (1979) as fol-

lows:

D = A + (B x ka)/(ka + k„)

where:

D = Fraction (DM, N, ADF or NDF) degradability (%)

l 54

1A = Fraction readily degraded (Z)

B = Fraction degraded at a measurable rate (Z)

kd= Degradation constant rate of fraction Bk„= Rumen turnover rate (assumed to be 0.05/Hour)

To analyze the data a general linear model procedure was

used.

To test predictability, estimated and observed parame-

ters were tested by means of a "t" test.

RESULTS AND DISCUSSION

1. Field Trial.

Information about yield and content of unensiled forages

are in Table 4. Early harvest resulted in a 58% reduction

in dry matter yield of the Boot treatment compared to

SD-Lo. Also the increase in height of the cutting bar

caused a 28% decrease in yield. These results indicate that

approximately half of the yield harvested at soft dough is

produced in the last month of growth. Edmisten (1985) and

Polan et al. (1968) also reported reductions of the dry

matter yield of approximately half when barley was har-

vested at boot compared to soft dough.

The dry matter percentage of the harvested material is

lower for the Boot treatment (31.5%), even after 2 days of

wilting. The soft dough treatments were similar in dry

matter content (34.2 vs. 35.3%) and within the recommended

range for direct cut (Gardener and Wiggans, 1961).

The crude protein percentage is 97% higher for the

earliest material and not different between soft dough

treatments. This is in agreement with the findings of Polan

et al. (1968) and Cherney and Marten (1982).

Water soluble nitrogen and true protein were not

different among treatments. This data is in close agree-

ment with the reports by Raymond (1969) because in most

55

I56

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I1

grasses (Graminae family) approximately half of the total

nitrogen is in the soluble form and most is non protein

nitrogen.

According to Cherney and Merten (1982) and Edmisten

(1985) boot stage is usually lower in NDF and ADF than soft

dough stage but this study showed no differences before

ensiling but did after. This lack of difference may be

explained by the closeness of the averages and the highA

variation of estimates. Cellulose content is the same for

the three treatments and hemicellulose is lower for the

SD-Lo treatment mainly due to both a lower NDF and a higher

lignin content.

Lignin is an important component because of its high

negative relationship with forage quality (Van Soest and

Moore, 1965). Also lignification of the fiber fraction has

been reported as a function of age of the plant (Cherney

and Merten, 1982). This explains the lower lignin content

of the younger material (Boot), as well as the tendency of

SD—Hi to be lower because the fraction left in the field

with the higher cut is composed of older leaves and stem

internodes.

Usually ensiled barley has enough substrate to promote a

good fermentation. The data shows no differences among the

treatments in soluble sugar content and all the treatments

are above 2.5% of water soluble sugars in the fresh weight,

1

ss T

suggested by Wilkins (1981) as the lower limit required to

assure a good fermentation.

2. Silaqe Evaluation.

Dry matter and fiber fractions of the silages are

presented in Table 5. The three treatments differ in dry

matter content and Boot stage has the highest moisture.

Differences between the soft dough stages may be due to the

lower content of grain of the lower cut (SD-Lo). All three

treatments had a dry matter content greater than 28% which

was recommended to prevent undesirable clostridial fermen-

tation (McCullough, 1978).

The cell wall content (NDF) is higher for the more

mature stages of growth (SD-Lo and SD—Hi). This demon-

strates the amount of plant cell wall in the plant tissue

is a function of age (Van Soest, 1965), and is true even

though more starch (seeds) is present in soft dough barley.

ADF content has also been reported as a function of plant

tissue age (Van Soest, 1965). Increasing the cutting bar’ height also decreases ADF content by reducing the amount of

older material and also by increasing the proportion of

grain to forage of the harvested portion of the crop.

Lignin content is a function of the plant tissue age and

has frquently been mentioned as increasing without pla-

tauing at any stage of maturity (Cherney and Merten, 1982).

Nevertheless, leaving the older material in the

59 W

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field (SD-Hi) resulted in a decreased lignin content not

different than harvesting the crop at an early stage

(Boot). Cellulose content is the same for all treatments

irrespective of stage of growth or harvesting method. The

hemicellulose content is not different between growth

stages (Boot vs SD—Lo), but the higher cut is grater due to

a higher NDF and lower ADF and lignin content.

Data concerning nitrogen fractions of the silages is

presented in Table 6. Crude protein content is higher for

the Boot treatment compared with the more mature stage and

not different between soft dough treatments. This is in

close agreement with many reports in which crude protein

content declines with increased maturity (Raymond, 1969;

Cherney and Merten, 1982; Edmisten, 1985).P

The nitrogen insoluble in buffer solution (BUFFINSOL—N)

is lower for the material harvested at boot stage with the

higher CP content. All three silages had a nitrogen content

in the soluble fraction higher than 50%, which was reported

as typical of grass silages by McDonald and Whittenbury

(1973). This indicates extensive proteolysis during

ensiling.

The nitrogen insoluble in neutral detergent (NDIN) and

acid detergent solution (ADIN) are higher for the SD-Hi

than the Boot treatment. The nitrogen insoluble in acid

detergent but soluble in neutral detergent solution (NDIN

61 I

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62-

ADIN) is very similar for the three treatments (8.3, 7.3,

and 7.9% for Boot, SD—Lo and SD-Hi respectively) and is

considered as a completely available fraction for the

animal, but degradable in the rumen at a slower rate than

the completely soluble nitrogen (Krishnamoothy et al.,

1982). However the ADIN content is considered completely

unvailable for the animal or the rumen microbes and isregarded as a good indicator of protein damage in conserved

forages. Higher levels than ll to 15% of the total nitrogen

in this fraction are evidence of protein damage caused by

heating (Van Soest, 1982). In this particular case the

total available nitrogen (100-ADIN) ranges between 95 and

92.2% which indicates the ensiling process did not result

in extensive heat damage.

Total water soluble nitrogen was not different among the

three treatments mainly because of a high variation in the

estimates (CV= 22.0%). This estimate represents the

nitrogen fraction readily available for rumen utilization

and is very similar to the buffer soluble fraction. Water

soluble true protein (WSTP) content is lower for the Boot

treatment in respect to soft dough stages, nevertheless the

ensiling process seems to have increased this fraction

(2.28, 7.29 and 5.52 times for Boot, SD-Lo and SD-Hi

respectively) compared to the non ensiled material (Table

4). There is a tendency to increase water soluble protein

63

3per kg of dry matter (0.48, 0.64 and 0.80 for Boot, SD—Lo 1and SD-Hi respectively) and to reduce nonprotein nitrogen

with advancing maturity. Also WSTP tends to increase with a

higher cutter bar at harvest. However it is still a minor

component of the water soluble nitrogen.

Lactic acid, volatile fatty acids and pH of the silages

is summarized in Table 7. Lactic acid content was higher

for Boot than the soft dough treatments and tended to be

lower for the SD-Hi silage. This indicates an inverse

relationship with the dry matter content of the ensiled

materials as observed by McDonald and Whittenbury (1973).

According to McCul1ough (1978), lactic acid is positively

related to silage intake and except for Boot, silages were

below the lower limit of lactic acid content range for a

well fermented silage (1.5 to 2.5%). Acetic acid content1 was higher for Boot than the soft dough treatments and not

different between cutting heights. Soft dough treatments

had an acetic acid content within the range reported as not

detrimental to silage intake (0.5 — 0.8%). However, acetic

acid content of Boot silage may negatively affect dry

matter intake (McCullough, 1978).The propionic acid content was higher for Boot silage

and the content is in the recommended range only for SD—Lo

and SD-Hi silages (McCullough, 1978). As was the case with

acetic acid, the high propionic acid content of Boot111

64

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1

65silagemay constitute a negative factor affecting intake.

Isobutyric, butyric and isovaleric acids were not

different among silages and are considered as acceptable

for a good quality silage. Butyric acid alone is considered

as highly correlated with poor quality silage and low

intake (Gordon et al., 1964), and the best indicator of

clostridial fermentation. All three silages had butyric

acid contents well below the level (0.10%) at which it is

considered detrimental to silage intake.

The pH of the silages were not different among treat-

ments. Breirem and Ulvesli cited by McCullough (1978)

recommend a pH not higher than 4.2 for a good silage, but

other reports consider pH levels of 4.4 as an index of good

quality and stability in silages (Van Soest,1982). Best

results depend on interaction with moisture content of the

material.

Macromineral content of silages is presented in Table 8.

As a general trend the mineral content was higher for the

Boot treatment due to a dilution effect of the higher dry

matter yields as the plant matures (Cherney and Merten,

1982 and Raymond, 1969). Also for Calcium and Potassium

higher cutter bar height resulted in lower mineral concen-

tration likely due to greater grain to forage content.

However, Phosphorus did not increase with the higher cut

and higer grain content. Grains in general contain low

\

66 F

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67N

i

amounts of macrominerals.

Except for calcium, potassium and sodium there was no

effect of the cutting height on the mineral content of the

silages. These three minerals are in higher concentrations

where active growth and cell division is taking place.

Therefore, they are in a relative lower concentration in

the plant heads (Raymond, 1969).

VThe NRC (1982) does not cover the mineral composition of

all the stages of maturity of barley but comparing the

composition of SD-Lo it is very similar to that of the

tables except for potassium and sodium. Potassium is higher

and sodium lower than the referenced tables. Sulfur content

is also very similar to that reported in the National

Research Council (1982) tables. Calculation of the nitrogen

/ sulfur ratio resulted in 11.6, 10.4 and 10.1 for Boot,

SD—Lo and SD-Hi respectively. They are very close to the

reported N/S average protein ratio of 10/1 (Nationa

Research Council, 1988).

Table 9 contains the average recovery of dry matter,

crude protein and neutral and acid detergent fiber from

each silo.

The data has no statistical evaluation because there

were no repetitions of silos. This data accounts mostly for

fermentation and effluent losses, but also includes

losses during the silo unloading.

68

N

Table 9. Dry matter, crude protein, neutral detergentfiber and acid detergent fiber recovered from thesilos as % of the original amounts stored foreach of the barley treatments.

Boot SD—Lo SD-Hi

Dry Matter (%) 88.6 90.2 100.3

Crude Protein (%DM) 77.8 85.5 87.6

NDF (%DM) 78.6 91.2 96.5ADF (%DM) 97.3 101.5 107.3

69 ' Ä

As a general trend and for all the fractions considered

recovery shows an association with dry matter content of

the ensiled materials (Table 5). Crude protein tends to be

the individual fraction most affected by ensiling, which is

in accordance with the report by McDonald et al. (1973).Since most of the protein is in the soluble portion of the

silage this may cause a greater loss due to seepage. The

tendency for the fiber fractions was to be less affected,

especially ADF. According to McDonald and Whittenbury

(1973) only hemicellulose may be partially affected by the

ensiling process and may be the explanation for NDF tending

to be more affected than the ADF fraction.

3. Heifer Digestibility Trial.

Table 10 contains the average composition of silages fed

growing Holstein heifers during the digestibility trial.

Since this data is the result of the analysis of one

composite sample per treatment there is no statistical

analysis.

Dry matter, crude protein and ash contents follow the

tendency already described for these treatments (Tables 5

and 6). Ether extract tends to be higher in younger

material (Boot) and may be a result of higher pigment

content (Boot).

Nitrogen free extract is higher for the treatment with

Ihigher organic matter and lower crude protein, ether

i

7Ol

extract and crude fiber (SD-Hi). This is mainly due to

method of calculation, but it also coincides with theincreased grain content of the soft dough silages. The

detergent fiber fractions (NDF and ADF) follow the trend

previously described in Table 5.I

The coefficients of In Vivo apparent digestibility of

the different silage fractions are presented in Table ll.

Except for Ether Extract all fractions were more digestible

for Boot compared to the soft dough treatments. No differ-

ences were found between soft dough treatments except in

ether extract and N free extract.

Results agree with those reported by Schneider and Flatt

(1975) in which younger material with less lignin tended be

more digestible than older material. This is particularly

true for crude fiber and consequently organic and total dry

matter. NDF and ADF are also more digestible for Boot than

for soft dough perhaps due to less lignin content.

The crude protein fraction of the soft dough stages

shows a very low apparent digestibility, which may be

explained by the low crude protein (Table 8) and high

indigestible dry matter of these treatments. According to

Schneider and Flatt (1975) the endogenous metabolic

nitrogen content of the feces increases as the intake of

indigestible material increases. Also when crude protein

level of feeds is low, endogenous nitrogen is a relatively

>

71Table10. Dry matter, proximate components and acid andneutral detergent fiber fractions of the compos-ite samples of the silage treatments fed duringthe digestibility trial.

Boot SD—Lo SD—Hi

Dry Matter (%) ——ä2??—__—i§;E?—_—Z3T0—

Organic Matter (%DM) 89.5 92.5 95.6

Crude Protein (%DM) 19.0 8.1 7.9

Ether Extract (%DM) 2.9 2.1 2.0

Estimated Crude Fiber (ZDM) 25.8 27.6 24.6

N Free Extract (%DM) 41.8 54.6 61.0

Ash (%DM) 10„5 7.5 4.4

ADF (%DM) 30.9 33.2 29.3

NDF (%DM) 46.5 50.0 46.7

1

72 1

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1

73importantcomponent of total fecal nitrogen, thus, reducing

the coefficient of apparent digestibility. Therefore, true

digestibility may be greater than estimated for both SD-Lo

and SD-Hi.

Total digestible nutrients was estimated according to

the method of Weende (Schneider and Flatt, 1975). This done

by adding the product of the proximate fractions (crude

protein, crude fiber, nitrogen free extract and ether

extract) discounted by their respective coefficient of

digestibility. Ether extract is multiplied by 2.25 to

compensate for its higher caloric content. Total digestible

nutrients content is higher for the Boot treatment as a

result of higher digestibility coeficients for most of the

proximate fractions and is an index of the available energy

of the feedstuffs.

4. Lactating Cow Feeding Trial.

The average compositions of the six experimental diets

fed to lactating dairy cows are summarized in Table 12. The

main differences in dry matter content were among diets

made with the same silage treatment but with different

concentrate content. The general tendency was for diets

with more concentrate to be drier due to addition of arelatively dry feed. On the other hand diets with high

silage content will be wetter.

There were no differences in crude protein content

74

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75 f

among diets because the diets were formulated to be

isonitrogenous. However there was some Variation in diet

protein due to changes during the feeding trial. Diets C,

D, and F tended to be lower than target amount.

The least TDN (determined by VPI Forage Testing Lab) was

in diet C (SD-Lo with a forage concentrate ratio of 75/25).

However the tendency was for higher TDN to be associated

with level of concentrate of each diet rather than with the

forage component. Because net energy of the diets was

estimated from TDN content, NEL follows the same pattern.

The ADF content of diets reflects the forage component.

Diets containing SD—Lo silage had the higher fiber content

for both, the more concentrated (60/40) and the less

concentrated (75/25) formulations. For diets containing

either Boot or SD—Hi silages the main difference in fiber( content was due to the concentrate level of each diet

rather than differences in forages. This is in agreement

with results about silage composition reported in Table 5.

Table l3 summarizes results about dry matter intake,

milk production and milk composition obtained when the

experimental diets were fed. There were no differences in

average dry matter intake among the diets. However, except

for diet C, there was a slight tendency towards a higher

intake with the more concentrated diets (diets B, D and F),

which may be due to lower fiber (ADF) content. Dry matter

76I

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77

I

intake expressed as a per cent of body weight was not

different among diets and except for the diet E, were lower

than the average of 3.2% used by the NRC (1988). The high

temperatures recorded during this experiment (July and

August) may have affected the dry matter intake, especially

those higer in fiber (A, C and E) with higher fermentative

heat production.

There were differences in milk yield among diets, but

yields tended to relate more to energy density of the diets

or the concentrate content rather than forage source. There

was a significant effect of concentrate amount, but no

differences due to forage source. In other words higher

concentrate amounts stimulate more milk production. There

were no difference in 4% fat corrected milk yield and again

the tendency grouped the averages by concentrate content

rather than forage source. There were no differences in

milk components among the diets.

Gross Efficiency expressed as kg of milk produced per kg

of dry matter consumed compares the ability of the differ-

ent diets to promote milk production. Therefore, consider-

ing milk production and DMI simultaneously did not result

in significant effects. There were no differences in this

index. Energy Efficiency index compares diets in terms of

isocaloric units of milk produced (kg of 4% ECM) per unit

of availble energy consumed (kg of TDN). There was no

III

I78 I

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79 I[I

Istatistical difference among the experimental diets, but

there was a tendency that suggests the diets containing the

more digestible Boot silage (A and B), were slightly more

efficient in using this energy for milk production.

The main effect of experimental diets was on body weight

change. The low concentrate diets containing soft dough

silages were able to promote body weight gain, but diets

with higher concentrates promoted a certain degree of body

weight loss. Cows fed both diets containing Boot silage had

body weight loss. Polan et al. (1968) reported observed

body weight gains in their experiment were related to

different intakes, but in the present study there was no

clear relationship between dry matter intake and body

weight change. Also intake of TDN or NEL cannot fully

explain the body weight changes recorded. According to the

National Research Council (1988) 1 kg of body weight lost

or gained is equivalent to 6.8 kg of 4% ECM. Correcting

treatments for this figure, assuming 0 body weight change,

the 4% ECM productions would be 20.2, 21.7, 24.3, 22.2,

24.1 and 24.2 for diets A, B, C, D, E and E respectively.

This indicates less production for Boot silage when body

weight changes are taken into account.

Average daily intake of total digestible nutrients was

not different among the experimental diets, but appeared

[related to higher milk production and body weight loss.

801

Acid detergent fiber intake showed differences only between

the extremes. Table 14 presents the same information as

Table 13 but grouped according to forage and concentrate

effects. The tendency was for dry matter intake to be

associated with the dry matter content of the forages. The

milk yield and 4% fat corrected milk, however, tended to be

associated with the energy content of the silages. Gross

efficiency and energy efficiency tended to be higher for

the Boot and lower for SD-Lo silage and were associated

with the higher and lower energy density respectively.

Body weight change showed different patterns for the

treatments. Soft dough silages maintained body weight while

the Boot treatment recorded a body weight loss. Cows fed

Boot silage had body weight loss associated mainly with

higher milk yield and lower dry matter intake.

Intake of total digestible nutrients is not different

among the treatments, and intake of acid detergent fiber is

different only between Boot and SD—Lo. This difference is

the result of lower fiber content and dry matter intake of

the diets containing Boot silage.

Table 15 contains correlation coefficients for the

variables measured in this study. These variables are dry

matter, total digestible nutrients, acid detergent fiber

percentage, milk yield, fat corrected milk yield, milk fat

content, dry matter intake, TDN intake, ADF intake and

81

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body weight change.

According to relationships among variables of Table 15

TDN and DM content of diets were positively related. This

was because diet DM Variation was partially due to concen-

trate content which in turn was an important determinant of

energy. Since TDN is estimated from the ADF content of the

diets these two components were strongly associated.

Milk yield (Milk) showed no association with diet

components, but as expected the most important parameters

in determining milk yield were total dry matter intake

(DMI) and intake of total digestible nutrients (TDNI). The

positive relationship between milk yield and intake of ADF

is probably a result of dry matter intakes reported already

(Table 13), indicating that cows were still able to

increase comsumption because ruminal capacity was not

reached (Forbes, 1970). The main reason for low intake was

high temperatures recorded during most of the experimental

period. Fat corrected milk yield (FCM) was related to the

TDN content or energy density of the diets and strongly

associated with the total intake of dry matter, TDN and

ADF. Milk fat Z showed no relationship with diet or intake.

Intake of TDN had no relationship with the TDN content

of diets, but was highly related to the total dry matter

intake (DMI). On the other hand intake of ADF had no

relationship with total dry matter intake (DMI) but was

l

83 4

correlated to the ADF content of the diets.

Body weight change was best explained by silage source,

and TDN and ADF contents of the diets. Diets containing

SD—Lo silage had greater body weight gain and ADF content.

Also SD—Lo was lower in TDN content. Diets containig Boot

silage were higher in TDN and lower in ADF and recorded the

greater body weight loss. With the recorded intakes,

affected by the ambient temperature, it is very difficult

to explain the body weight changes obtained.

5. Ruminal Degradability Trial.

An analysis of variance using ruminally cannulated cows

as blocks was used to analyze data for ruminal degradabil-

ity. To describe ruminal degradability of the silages, the

experimental diets and the predicted experimental diets the

following parameters were used:

A = Readily available fraction

B = Degradable fraction (at a measurable rate)

C = Undegraded residue after 72 hours of incubation

D = Overall degradability calculated according to the

Orskov equation, using a rumen turnover rate of

.05%/hour.

Kd= Degradation rate constant (%/hour)

Parameters A, B, C and D are expressed on a dry matter

basis, and are presented in Table 16.

Increase in maturity increases the highly soluble DM

84

Table 16. Ruminal degradability parameters, A, B, C, D andK. for the dry matter of the experimentalsilages.

Signif.Parametersz Boot SD—Lo SD-Hi S.E.‘ Level

A (ZDM) 43.4. 46.0. 52.0. 0.264 *B (ZDM) 46.2. 30.6. 26.6. 0.268 **C (ZDM) 10.4. 23.4. 21.4. 0.045 **D (ZDM) 68.6. 57.8. 62.5. 0.270 **K. (ZDM/hr) 0.060. 0.032. 0.033. 0.001 **

Different letters in the same row indicate statisticallydifferent means.

Significance Level: **=(P$0.01), *=(P$0.05), NS= Nonsignificant difference.‘

Standard Error of the Estimates.’A=Readily available fraction (Z).B=Degradable fraction at a measurable rate (Z).C=Undegraded residue after 72 h incubation (Z).D=0veral1 degradability (0rskov equation), (Z).K.=Degradation rate constant (Z/h).

V

85fraction (A) and the unavailable fraction (C) at the

expense of the B fraction. The higher cut (SD-Hi) did not

reduce the undegraded residue (C), but the higher grain

content increased the highly soluble fraction (A) compared

to SD-Lo. As a consequence of a higher B fraction and a

much higher degradation rate (Kd) Boot silage had a higher

overall DM degradability than soft dough. The higher cut

silage dry matter (SD-Hi) was more degradable than normal

cut, due to a greater content of the highly degradable

fraction. Most likely this is a result of a greater grain

to forage ratio. Table 17 contains the nitrogen compound

degradabilities of the silage treatments. There were no

differences in highly soluble (A), degradable (B) or

unavailble (C) nitrogen fractions. All silages had roughly

75% of the nitrogen in a very degradable form which is

coincident with the observations by McDonald and Whitten-

bury (1973). The overall degradability of nitrogen was

extensive for all silages but the younger material (Boot)

had the greatest. Boot silage contained less fiber (ADF)

and lignin (Table 5) and less unavailable nitrogen bound to

the fiber. The extent of degradation is similar to to those

reported in alfalfa and corn silages (Janicki and Stal-

lings, 1988).

The relatively high proportion of nitrogen in the

undegradable fraction (C) compared to nitrogen bound to ADF

l

K

86

Table 17. Ruminal degradability parameters (A, B, C, D andKd) of nitrogen compounds of the experimentalsilages.

Signif.ParametersZ Boot SD—Lo SD-Hi S.E.Z Level

A (%N) 77.4 74.9 78.1 2.707 NS

B (%N) 16.8 10.6 8.3 4.755 NS

C (%N) 5.8 13.7 13.6 2.164 NS

D (%N) 89.3. 76.9. 80.0. 1.432 *Kd (%N/hr) 0.123 0.029 0.088 0.016 NS

Different letters in the same row indicate statisticallydifferent means.Significance Level: **=(P$0.01), *=(P$0.05), NS= Non sig-nificant difference.Z Standard Error of the Estimates.Z A=Readily available fraction (%).

B=Degradable fraction at a measurable rate (%).C=Undegraded residue after 72 h incubation (%).D=0verall degradability (0rskov equation), (%).Kd=Degradation rate constant (%/h).

87

(ADIN) in Table 6 may be due to microbial contamination.

Also the larger the undegraded fiber fraction the more

likely the microbial contamination because of the ability Äof microbes to adhere to the fiber.

The degradation rate constants were not different among

treatments mainly due to the high variation of this

estimate. Boot did have the numerically largest but non

significant degradation rate, however.

Table 18 presents the results of the degradation of the

ADF fraction of the silages. As expected there are no

relevant amounts of rapidly degradable fiber in the

silages, but the degradable pool is different. Degradation

of ADF is highest for younger and less lignified material

(Boot) and not different between soft dough silages. Also

the residue after 72 hours of incubation (C) was different

but only between stages of maturity. The overall degrada-

tion of the ADF fiber is different and approximately double

for the Boot silage mainly due to a larger B pool and a

faster degradation rate of this pool.

Table 19 containes results of the ruminal degradability

of the NDF fraction of the experimental silages.

The degradability parameters for NDF are very similar to

those of ADF (Table 18) indicating the main determinant of

NDF degradability is the composition and amount of ADF.

Boot NDF fiber is characterized by a relatively large

es “

Table 18. Ruminal degradability parameters (A, B, C, D andKd) of the Acid Detergent Fiber (ADF) fraction ofbarley silages.

SignifParameters1 Boot SD-Lo SD-Hi S.E.1 Level

A (ZADF) 0.0 4.6 7.6 2.177 NS

B (ZADF) 86.1. 52.0. 49.5. 2.088 **C (ZADF) 17.1. 43.4. 41.4. 0.881 **D (ZADF) 44.2. 20.9. 22.8. 2.218 *K. (ZADF/hr) 0.053. 0.024. 0.021. 0.002 **

Different letters in the same row indicate statisticallydifferent means.Significance Level: **=(PS0.01), *=(P$0.05), NS=NonSignificant Difference.1 Standard Error of the Estimates.1 A=Readily available fraction (Z).

B=Degradable fraction at a measurable rate (Z).C=Undegraded residue after 72 h incubation (Z).D=0verall degradability (0rskov equation), (Z).Kd=Degradation rate constant (Z/h).

89 „

Table 19. Ruminal degradability parameters (A, B, C, Dand Kd) of the Neutral Detergent Fiber (NDF)fraction of barley silages.

Signif.Parametersz Boot SD—Lo SD-Hi S.E.1 Level

A (ZNDF) 0.0 5.5 8.5 1.148 NS

B (%NDF) 86.2. 53.0b 50.3b 1.613 **C (%NDF) 17.8b 41.5. 41.2. 0.473 **D (ZNDF) 45.1. 24.2s 26.4b 2.491 *Kd (%NDF/hr) 0.056. 0.028b 0.028b 0.002 *

Different letters in the same row mean statisticallydifferent means.Significance Level: **=(P$0.01), *=(P$0.05), NS=NonSignificant Difference.1 Standard Error of the Estimates.2 A=Readily available fraction (%).

B=Degradab1e fraction at a measurable rate (%).C=Undegraded residue after 72 h incubation (%).D=0vera1l degradability (0rskov equation), (%).Kd=Degradation rate constant (Z/h).

90 )

degradable pool (B) compared to soft dough silages. This is

a result of a relatively low undegradable residue (C) and a

degradation rate constant twice as fast. Consequently the

overall degradability of NDF of Boot silage is almost

double that of the later harvested treatments.

According to the biphasal model to explain intake

proposed by Forbes (1977), Boot silage would be the silage

with the highest theoretical intake because it has the

smallest undegradable pool. Also it has the largest B pool

of dry matter and fiber but the fastest rate of degrada-

tion, which should promote higher intake.

Rumen degradabilities for dry matter and nitrogen of the

concentrate ingredients (Soybean Meal and Shelled Corn) fed

to lactating cows is presented in Table 20. The nitrogen

and the dry matter degradability data of shelled corn and

soybean meal of this experiment are very similar to that

reported by Zerbini (1984), except Soybean Meal in this

study has an A fraction 40% larger and a B fraction 27%

smaller. Therefore, Soybean Meal used in this study would

be expected to be more rapidly utilized.

Table 21 presents data of dry matter degradability of

the experimental diets. The degradability of dry matter was

greatest for diets A and B (Boot silage), intermediate for

diets E and F (SD-Hi silage) and least for diets C and D

(SD-Lo silage). This demonstrates the strong influence of

l

I91 I

I

Table 20. Ruminal degradability parameters (A, B, C, D andKd) of the dry matter and the nitrogen of theSoybean Meal (SBM) and Shelled Corn (SCorn),used as concentrate ingredients of the exper-imental diets.

DRY MATTER NITROGEN

Parameters SBM Shelled ; SBM ShelledCorn : Cern

A (Z) 45.2 40.0 ; 34.7 37.6B (Z) 52.2 59.1 : 64.5 64.2C (Z) 2.6 0.9 : 0.8 1.2D (Z) 78.1 78.7 : 76.9 72.7Ka (Z/hr) 0.086 0.095 : 0.096 0.068

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93 E

the forage component of the diets. There were no differ-

ences among diets in soluble fraction (A) or degradation

rate constant (Kd) but there were differences in undegrad-

able residue (C) and fraction B (Table 16).

Table 22 presents the information about nitrogen

compound degradability of the experimental diets. The

nitrogen degradability (D) of all experimental diets was

very high and not different among treatments, neither was

the degradation rate constant (Kt). According to the NRC

(1988) and the dry matter intake recorded in this exper-

iment Undegraded Intake Protein of the experimental diets

was below the requirements (498, 510,371, 277, 382 and 414

g UIP/ cow /d for diets A to F respectively) for the levels

of production recorded. The residual undegraded nitrogen

was lower for diets A and B due to the higher degradability

of the nitrogen and fiber components of Boot silage (Tables

17 and 19). There were also differences in the size of the

degradable pool (B) but these differences were more

associated with the concentrate content of the diet rather

than forage source. The differences in soluble fraction (A)

were also more related to concentrate content than forage

content of the diets.

Table 23 presents data of ruminal degradability of ADF

of the experimental diets. There were no differences in

readily degradable pool (A) or in degradation rate constant

94 ,II

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(Kd) among treatments. Consistent with differences among

forage components (Table 18), the size of degradable pool

(B) and undegraded residue (C) were different. This

resulted in differences in the overall degradability (D) of

ADF. Since the main sources of ADF are the silages,

differences in degradablity tended to group treatments by

forage source.

Results about ruminal degradability of the NDF of the

experimental diets is presented in Table 24. Again as for

ADF there were no differences in readily degradable

fraction (A) or degradation constant rate (Kd) and due to

the high variation of the estimates the overall degradabil-

ity (D) was not different among diets.

As for ADF the main differences in NDF degradability

were in the sizes of degradable (B) and undegradable (C)i

pools. Differences tended to group the diet treatments

according to forage source, showing that Boot NDF had a

greater degradable portion and smaller undegradable residue

than the later stages.

Table 25 presents the proportion of different ingre-

dients of the experimental diets on a dry matter basis.

These proportions were used with ruminal degradability of

single ingredients to predict the degradability of DM and N

compounds of complete experimental diets.

[ Table 26 contains the estimated parameters of ruminal

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98 1

Table 25. Composition of the experimental diets expressedas per cent of each ingredient in a dry matter‘ basis. ——--—--—-- Experimental Diet —--————-—-

Ingredient A B C D E F

Silage 89.7 81.3 88.6 79.8 86.8 77.7

Soybean Meal 4.3 5.6 9.8 10.7 11.5 12.2Shelled Corn 4.6 11.5 0.0 7.7 0.0 8.1Mineral Mix 1.4 1.6 1.6 1.8 1.7 2.0

99degradabilityof dry matter of the experimental diets.

Predicted paramenters of Table 26 were statistically

compared to those observed (Table 20) using a t test.

Predictability of DM degradability of complete diets waspoor. Only undegraded residue (C) and degradation rateconstant (Kd) tended to be more predictable compared to

other parametes. The low predictabilities obtained may be

due to low number of repetitions per estimate and high

variability of some parameters. However, almost all the

estimated parameters were lower than the observed values

probably due to a slower degradability of the ingredients

incubated individually than in complete diets. It may be

when feed sources containing protein, energy, or minerals

are combined there is a stimulation of DM utilization in

the rumen compared to estimates based on single ingredient

incubation.

Predicted parameters of degradability of nitrogen of the

experimental diets is presented in Table 27. Predictability

of the different N parameters was relatively low. There was

a tendency to predict the readily degradable nitrogen

fraction (A) better than others.

In this case except for the undegraded residue (C) the

predicted were always higher than the observed parameters

in Table 2l. Apparently the nitrogen of the single ingre-

dients had a smaller readily degraded fraction (A) and

100

Table 26. Predicted parameters of ruminal degradability(A, B, C, D and Kd) of dry matter of theexperimental diets.

Param.1 A B C D E F

A 43.3 43.1 46.0 43.1* 51.2 50.2

B 47.0 48.0 32.7 31.6 21.6 32.4

C 9.8* 8.9* 21.3 19.3* 19.2* 17.4*

D 69.5 70.3 59.8 56.9* 64.4 65.8*

Kd 0.064* 0.066* 0.037* 0.037 0.040 0.045*

Observed and predicted parameter are not statisticallydifferent with the following probability:a=(P20.75), b=(P20.80), c=(P20.95) and d=(P20.0l).1 A=Readily available fraction (%).

B=Degradable fraction at a measurable rate (%).C=Undegraded residue after 72 h incubation (%).D=0verall degradability (0rskov equation), (%).Kd=Degradation rate constant (%/h).

I

101 IV

was degraded at a slower rate (Kd) when individually

incubated compared to incubation in complete diets. The

greatest differences between actual versus predicted

overall degradabilities was in diets C, D, E, and F. These

diets contain the greatest amount of soybean meal. Diets A

and B contain less. It may be the forage nitrogen in

complete diets is slowing breakdown of soybean meal

nitrogen , thus, reducing total breakdown resulting in more

protein or N being undegraded in the rumen.

Data indicate that using analysis of single ingredients

to predict total breakdown in complete diets is question-

able.

1 102N

Table 27. Predicted parameters of ruminal degradability(A, B, C, D and Kd) of nitrogen of the exper-imental diets.

Param.* A B C D E F

A 73.6* 70.3* 73.1* 67.3* 72.4* 68.8*

B 21.0 24.7* 21.6* 21.8* 22.4 26.4*

C 5.4 5.0* 5.33* 4.8* 5.2* 4.8*

D 88.0 86.7 88.1* 82.3* 87.9 86.4*

Ka 0.112 0.115 0.121 0.112 0.120 0.115

Observed and predicted parameter are not statisticallydifferent with the following probability:a=(P20.75), b=(P20.80), c=(P20.95) and d=(P20.01)‘

A=Readily available fraction (Z).B=Degradable fraction at a measurable rate (Z).C=Undegraded residue after 72 h incubation (Z).D=0verall degradability (0rskov equation), (Z).Kd=Degradation rate constant (Z/h).

1

i 1SUMMARY AND CONCLUSIONS

Boot and soft dough raised cut reduced dry matter yield

per hectare and reduced fiber (ADF) content. Boot harvest

increased crude protein. However, crude protein and total

digestible nutrient yield per hectare was higher for soft

dough low cut.

In general silage composition was in accordance with

the composition of the fresh material. The fermentative

characteristics pH, lactic acid, volatile fatty acids,

butyric acid content and nitrogen bound to acid detergent

fiber were considered acceptable for the three treatments.

Except for ether extract all the In Vivo digestibility

coefficients were higher for the boot harvest and no dif-

ferences were found between soft dough stages. As a result

boot silage had a higher TDN content.

There were no differences in total dry matter intake,

milk fat, 4% fat corrected milk or TDN intake among silage

treatments. Differences in milk yield tended to group

treatments according to concentrate content rather than

silage components. Soft dough treatments maintained while

boot silage promoted body weight loss. The low and not dif-

ferent intakes obtained in this study suggest a strong

influence of the hot weather depressing the voluntary

103

1104 I

intake of the experimental diets.

The ruminal degradability of dry matter, acid detergent

and neutral detergent fiber of Boot silage was higher than

that of the soft dough silages. Dry matter degradability of

soft dough raised cut was highe than soft dough low cut.

The undegraded residue after 72 hours of incubation was

also higher for the soft dough silages.

The readily degradable nitrogen fraction of all silages

was high and not different among silages. Boot had a lower

undegradable residue, a higher degradation rate and

consequently a higher overall degradability of nitrogen

compounds than soft dough silages.

Dry matter and nitrogen commpound degradability of the

experimental diets were highly influenced by forage ingre-

dient characteristics. All experimental diets were high in

readily degradable nitrogen making the undegraded intake

protein lower than the tabulated requirements.

Prediction of dry matter and nitrogen degradability of

the complete diets based on degradability of single ingre-

dients was poor and restricted to some parameters such as

undegradable residue and rate constant for dry matter and

readily degradable nitrogen. Dry matter degradability was

greater when complete diets were incubated versus individ-

ual ingredients indicating more extensive rumen digestion.

Nitrogen compound degradability was less when complete

l105 1

11

diets were incubated versus individual ingredients and may

be a result of sparing of soybean meal breakdown by the

highly degradable silage nitrogen. Incubation of single

ingredients did not give good estimates of rumen degrada-

tion compared to incubation of complete diets.

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APPENDIX

114

115 k

Table A1. Macro and micro mineral contents of barleytissue sampled from the three fields of theexperiment on 4/01/88.

PT HB Wt

Nitrogen (Z) 4.06 4.06 2.94Sulfur (Z) 0.20 0.33 0.25Phosphorus (Z) 0.66 0.47 0.49Potassium (Z) 3.05 3.19 3.25Magnesium (Z) 0.32 0.16 0.16Calcium (Z) 0.65 0.36 0.34

lSodium (Z) 0.18 0.12 0.07

Boron (ppm) 12 11 10Zinc (ppm) 38 32 24Manganese (ppm) 29 19 19Iron (ppm) 81 63 58Copper (ppm) 4 8 6Aluminium (ppm) 100 80 70

Table A2. Composition and nutrient content of thepre—experimental diet used between 6/27/88and 7/13/88.

Ingredient Per Cent (As fed basis)

Barley Silage 79.4

Dry Shelled Corn 10.2

Soybean Meal, 44Z 8.9

Mineral Mix 1.5

Nutrient Content:- Crude Protein 16Z- Energy Density 1.61 Mcal NEL/ kg DM— Fiber content 20Z ADF

116 Z

I

Table A3. Nutritive composition of the concentrateingredients used in the formulation of theexperimental diets.

Soyben Meal Shelled Corn

Dry Matter (%) 90.9 88.8Crude Protein (%) 45.6 9.7ADF (%) 13.4 6.0TDN (Estimated) (%) 80 85NEL (Mcal/kg DM) 1.74 1.87

Table A4. Composition of the mineral mix (VPI DairyMineral) supplemented in the feeding trialand In Vivo digestibility trial.

Phosphorus (P) Min. 6.50%Calcium (Ca) Min. 16.50%Calcium (Ca) Max. 19.80%Salt (NaCl) Min. 3.50%Salt (NaCl) Max. 5.50%Magnesium (Mg) Min. 2.50%Sulfur (S) Min. 3.60%Manganese (Mn) Min. 0.125%Zinc (Zn) Min. 0.15%Iron (Fe) Min. 0.03%Copper (Cu) Min. 0.015%Iodine (I) Min. 0.005%Cobalt (Co) Min. 0.003%Selenium (Se) Min. 0.0005%Vitamin A IU/Lb. Min. 50,000Vitamin D-3 IU/Lb. Min. 25,000Vitamin E IU/Lb. Min. 500Sodium Bicarbonate (by weight) 22%

-1„1_........................................................------J

117

Table A5. Nutritive composition of the barley silageused during the pre experimental period ofthe In Vivo digestibility trial.

Dry BasisDry Matter (Z) 35.6Crude Protein (Z) 9.2Acid Detergent Fiber (Z) 27.8TDN (Estimated) (Z) 65NE Lactation (Mcal/kg DM) 1.41

Table A6. Typical analysis of variance table foryields and composition of the harvested mate-rial of the field trial.

Source of Variation Degrees of Freedom

Treatments 2Blocks 5

Error 10

Table A7. Typical analysis of variance table for silagecomposition.


Treatments 2

Error 9

118TableA8. Typical analysis of variance table for diges-I tibility coefficients of proximate components· and TDN content of the silages.

ISource of Variation Degrees of Freedom

Treatments 2I Blocks 3

Error 6

Table A9. Analysis of variance table for milk produc-tion, milk components, dry matter intake andbody weight change.


Treatments 5Blocks 5

I Error 25

Table A10. Analysis of variance table to test milkproduction, milk components, dry materintake and body weight change according toforage source and concentrate level of theexperimental diets.


Silage 2„ Conc. Level 1

Silage x Conc. Level 2Blocks 5

I Error 25

119

Table A11. Average monthly temperature (QC) and totalprecipitaion mm (rainfall and snowfall) ofthe growing period of barley crop and feed-ing experiment.

Month - Year Temperature QC Rainfall (mm) Snowfall (mm)

October 1987 8.3 43.9 0.0November 1987 7.6 75.7 38.1December 1987 2.7 67.8 12.7January 1988 - 0.6 50.3 203.2February 1988 0.3 38.9 0.0March 1988 6.5 48.5 0.0April 1988 12.0 96.3 76.2May 1988 15.2 42.7 0.0June 1988 20.2 81.5 0.0July 1988 23.2 136.9 0.0August 1988 22.1 141.5 0.0September1988 16.1 105.2 0.0

1C,. · I I BARLEY SILAGE HARVESTED AT BOOT AND SOFT DOUGH STAGES FOR LACTATING COWS by Yamandu M....

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