Nutritional Considerations for Livestock on Rangelands Mort Kothmann Texas A&M University.

Nutritional Considerations for Livestock on Rangelands

Mort Kothmann

Texas A&M University

Herbivore Foraging Strategies

Do animals posses ‘nutritional wisdom’?

What is the evidence?

• Diet quality is higher than the average of forage available

• Avoidance of toxic species

• Learned/conditioned behaviors

• Animals remember what they learn

How do animals learn what to eat and what not to eat?

• Pre-natal influences

• From parent

• From peers

• Trial & error sampling behaviors

• Anatomical adaptations

• Physiological adaptations

Roles of Feedback in Foraging Behavior

• Ingestive effects– Morphological characteristics of forages

• Learning from post-ingestive feedback– Concentrations of nutrients

– Concentrations of toxins

• Learning from con-specifics involving trans-generational interactions– Genetic

– In utero

– Lactation

– Observation

Provenza & Cincotta (1993)

Evidence for Palatability

• Sheep learned to associate flavors with nutrients and preference for higher nutrient concentration

• Sheep did not develop an aversion to lower nutrient foods

• Cattle learned to prefer protein blocks when ingesting forage low in protein


Evidence for learned avoidance

• Intake of foods decreased as concentration of toxin increased

• Decreased intake of foods deficient in essential nutrients

• Increase intake of foods that rectify nutritional deficiencies


How do animals learn to associate the flavor of foods with post-ingestive

feedback?

• Food novelty

• Intensity of taste vs concentration of nutrient

• Relative amounts of two foods ingested

• Temporal sequence of food ingestion

• Prior experience with illness

• Prior experience with a salient flavor


Relating senses to post-ingestive feedback

• Affective processes– Taste– Responses are aversive or positive

• Cognitive processes– Odor and sight

• Combination of odor & taste results in stronger leaned behavior


Variation among individuals with a species

• Anatomical– Congenital – Environmentally conditioned

• Physiological– Congenital– Environmentally conditioned


Goats and Blackbrush

Blackbrush is a forage low in protein and high in condensed tannins (nutritionally similar to liveoak)

• PREFERENCE_Goats reared with mothers on blackbrush consumed 95% more than naive goats.

• PHYSIOLOGICAL_Experienced goats excreted 63% more uronic acids per unit of body weight

• MORPHOLOGICAL_Experienced goats had 30% greater reticulo-rumen mass


Models for foraging theory

“Darwin and Spencer thought that selection would necessarily lead to perfection, but species, people, and cultures all perish when they cannot cope with rapid change.” (Skinner 1981)

“Flexible responses and rapid adaptation are primary correlates of survival…”


Basic principles of adaptation

• Error-making

• Differential response

• Memory

(Note: These same principles are important in the design and use of TGM.)


Role of Adaptation and Learned Behaviors in livestock management• Naïve animals do not function as efficiently

in a new environment as animals who have one or more generations of conditioned experience in that environment

• Consider this when selecting and purchasing animals

Questions?

What is the source of the drive to eat (forage)?What is the source of the feedback responses?How does the animal integrate the many positive

and negative feedback signals generated during foraging?

How does an animal sense a nutrient deficiency and match diet selection with foods that rectify that deficiency?

How does an animal decide when to forage and when to stop?

Factors Regulating Intake of Grazing Animals

Short-term vs Long-term Regulation

P. Faverdin

1. Short-term reduction of intake does not necessarily indicate long-term reduction.

2. Animals require a “learning period” to adapt to changes in diet.

3. Dietary preferences shift towards optimum rumen functioning, rather than animal nutritional requirements as listed by “NRC Nutrient Requirements…”

Effect of Nutrients on Feed Intake

P. Faverdin

1. VFA have short-term effect to depress feed intake. All except propionate appear to relate to osmolarity.

2. Local anesthetics in rumen eliminate effects of acetate and butyrate but not propionate.

3. Propionate effects differ if infused into jugular vein (no effect) or hepatic vein (reduced intake). Apparently the effect of propionate is mediated in the liver.

4. Intestinal digestion of starch and glucose have little effect on intake regulation.

5. Protein in rumen stimulates intake.6. Fats and other substances that disrupt rumen function

decrease intake.

Glucose & Insulin in RuminantsP. Faverdin

1. Ruminants obtain little glucose from digestion products of normal herbivore diets.

2. Glucose is synthesized by gluconeogenesis in liver.

3. Glucose infused into the rumen has little effect on intake.

4. Insulin infusion produces short-term depression of intake for 30 minutes followed by compensatory increase in intake following one hour.

Role of Dietary Lipids in Intake RegulationP. Faverdin

1. Natural diets of herbivores are low in lipids.

2. High levels of lipids in diet disrupt rumen functions.

3. Infused lipids have immediate proportional effects in reducing short-term intake.

4. Mobilization of body lipids in response to lipolytic substances (B-adrenergic agonists) has no short-term effect but does reduce intake in the long-term.

5. Effect of free fatty acids on appetite in ruminants does not seem to be direct and mechanisms involved in intake regulation have not been identified.

Integration of Post-ingestive FeedbackP. Faverdin

1. Infusions and other artificial interventions may interfere with the animal’s ability to link post-ingestive responses with the diet consumed.

2. Animals “learn” through post-ingestive feedback and “anticipate” the meal’s post-ingestive consequences.

3. A treatment that has no effect over the very short term may modify the animal’s feed intake over the long term through a learning process.

4. Disruption of the animal’s equilibrium may cause short-term decreases in intake that disappear after several days, if the animal can adapt to the disequilibrium.

Role of N & ProteinP. Faverdin

1. Intake responds to the ratio of protein:energy in diet.

2. Very low or greatly increased NH3 in the rumen depresses intake.

3. Effects of protein on rumen functioning may stimulate appetite independently of its effects on rumen fill.

4. Ruminants prefer diets high in high-quality degradable N. (There must be a balance of DIP and UIP. MMK)

5. Ruminants rapidly learn to prefer diets that improve the functioning of the rumen.

Intake in relation to forage quality and protein supplementation

•N content in diet of >1% is required for optimal rumen function.•When diet CP is below 7%, intake and forage digestibility respond linearly to increases in dietary N•Above 7% CP in the diet, intake responses are primarily a function of metabolic responses in the ruminant at the tissue level.

From G. Carstens

Impact of bypass Impact of bypass protein supplementation protein supplementation (+/- urea) on intake of (+/- urea) on intake of low-quality forages in low-quality forages in

different climatic zonesdifferent climatic zones

Studies conducted Studies conducted in tropical or in tropical or

subtropical climatessubtropical climates

Studies conductedStudies conductedin temperatein temperate

climatesclimates

Leng, 1990; Nutr Res Rev 3:277Leng, 1990; Nutr Res Rev 3:277

Slide from Gordon Carsten

Receptors Involved in Intake Regulation (J.M. Forbes)

1. Receptor locations (stomach, intestines, liver and metabolizing tissues)

2. Property sensed (volume, osmolality, pH, and concentration of specific chemicals in digesta and portal blood)

3. Integration of signals in central nervous system (CNS) determines what food to eat and whether feeding should start or stop.

Gastrointestinal ReceptorsJ.M. Forbes

1. Stretch receptors are found in the anterior dorsal rumen wall.

2. Stretch receptors are also sensitive to chemicals, including VFA.

3. Physical responses to distension appear to be primarily related to short-term regulation; possibly with cessation of eating at a meal but not with initiation of eating.

4. There is no “fixed” physical capacity that limits intake. (Forbes 2000; Weston 1982; Pittroff & Kothmann 1999)

Osmotic Pressure Receptors

There are receptors in the GI tract that are sensitive to osmotic pressure, irrespective of the source. They apparently function to maintain homeostasis. Significant increases in osmotic pressure reduce intake.

They also function to regulate flow from the reticulum to the omasum and to the abomasum. Increased osmotic pressure in the rumen primarily functions to stop intake and to increase the flow of digesta within the GI tract.

Liver (J.M. Forbes)

The liver is the first organ which can sense and integrate the products of digestion after they leave the GI tract. In the ruminant, infusion of propionate functions to reduce intake similar to glucose infusion in the non-ruminant. Oxidation of VFA in liver depresses intake in the ruminant. Liver receptors appear to be primarily involved with cessation of individual meals rather than with long-term regulation of intake. Denervation of the liver leads to larger less frequent meals. Higher circulating nutrient levels result in less frequent meals. Supply of metabolites is monitored at the porta hepatis (entrance of the portal vein into the liver).

Adipose TissueLeptin is a hormone that provides feedback from levels of fat stores to various physiological functions that include: down regulation of intake, immune system function, and reproductive hormones. Leptin is a hormone secreted by adipose cells in proportion to their size. It circulates in the bloodstream and influences receptors in the brain. The discovery of leptin negates the need for the “physical limitation of intake by crowding of the rumen by fat” hypothesis that has long been postulated to explain why animals reduce intake as the percentage of body fat increases above threshold levels.

Short-Term RegulationShort-term intake regulation serves to maintain physiological parameters of the digesta and the blood within acceptable ranges. Systems that cause cessation of eating have received the most research attention. These include physical and chemical receptors in the rumen and chemical receptors in the liver. Osmotic and chemical receptor systems regulate the flow of digesta through the GI tract. Physical receptors in the anterior dorsal sac of the rumen may primarily regulate rumination relative to ingestion. These systems do not appear to have a significant role in regulating long-term intake.

Long-Term Intake

Systems that initiate eating and stimulate continued consumption of a meal have received less attention. These systems appear to be the primary mechanism for controlling long-term intake. Positive stimuli may relate to the rates of nutrient assimilation by metabolic tissues in the animal. Leptin would provide a negative feedback. Regulation of long-term intake probably involves a balance between positive feed-forward signals and negative feed-back signals.

Metabolic Regulation of Intake

•Intake is reduced by either severe deficiency or excess of a specific nutrient.

•Animals tend to eat protein to match their ability to synthesize and utilize protein in body tissues and milk

•Animals do not eat to a fixed demand for energy.

Protein as a regulator of energy utilization

The availability of protein regulates the use of energy for growth, lactation, reproduction, and other productive functions. When the supply of energy exceeds the availability of protein, excess energy in the form of VFA is either stored as fat or oxidized by the liver. Both of these processes result in negative feedback to intake.

General intake regulation(Pittroff & Kothmann 1999)

Potential vs Realized Energy DemandPittroff & Kothmann 1999

Potential energy demand (PED) – The animal’s PED is determined by its current physiological state and genetic potential for growth, lactation, and other productive functions.

Realized energy demand (RED) – PED is modified by climatic and handling stresses, pathogen effects, and properties of the diet itself (nutrient quantity and balance over time).

Effect of physiological Effect of physiological function on efficiency of ME function on efficiency of ME

utilizationutilizationPhysiological ME for Diet ME Diet ME Body tissuePhysiological ME for Diet ME Diet ME Body tissuefunction maintenance† to milk to body to milkfunction maintenance† to milk to body to milk

Lactating 122 64.4 74.7 82.4

Nonlactating 100 -- 55.0 --

††kcal/BWkcal/BW.75.75

Moe et al. (1981); JDS 64:1120. Data generated from Moe et al. (1981); JDS 64:1120. Data generated from energy balance experiments involving measurements of 350 energy balance experiments involving measurements of 350 lactating and 193 nonlactating cows. lactating and 193 nonlactating cows.


Effect of physiological function on Effect of physiological function on efficiency of ME utilizationefficiency of ME utilization

MilkMilk

FatFatStorageStorage

FeedFeed

75%75%lactatinglactating

82%82%

55%55%drydry

Direct ME use: 64%Direct ME use: 64%

Fat--late lactation:Fat--late lactation: 75 x 82 = 62% 75 x 82 = 62%

Fat--dry period:Fat--dry period: 55 x 82 = 45% 55 x 82 = 45%


Impact of VFA profile on efficiency of ME Impact of VFA profile on efficiency of ME useuseInfused VFAs singly or in mixes into rumen of sheep fed Infused VFAs singly or in mixes into rumen of sheep fed hay dietshay diets

32.9

56.3

61.9

31.8

58.1

0 10 20 30 40 50 60 70

Acetate

Propionate

Butyrate

Mix--75% acetate

Mix--25% acetate

Partial efficiency of ME utilization, %

Armstrong and Blaxter (1957, 1958, 1961)Armstrong and Blaxter (1957, 1958, 1961)

Concept established that net efficiency of ME use for growth was greater for diets providing more propionate & less acetate acid.


Effect of basal diet on efficiency of acetate Effect of basal diet on efficiency of acetate use--use--Acetate was infused into rumen of dairy Acetate was infused into rumen of dairy cowscows

Exp I; both diets pelleted; Exp II hay fed in long form, Exp I; both diets pelleted; Exp II hay fed in long form, concentrates fed in meal form concentrates fed in meal form (Tyrrell et al., 1976; EAAP 19:57Tyrrell et al., 1976; EAAP 19:57)


Effect of level of intake on Digestible EnergyEffect of level of intake on Digestible Energy


Effects of ambient temperature on Effects of ambient temperature on digestibility in ruminantsdigestibility in ruminants

shorn sheep

unshorn sheep

• Average decrease

in digestibility

per ˚C decrease

is equal to .18%

[NRC, 1981]• Occurs in both

ruminant and

nonruminant

animal species


Effect of level of metabolizable energy Effect of level of metabolizable energy intake on liver massintake on liver mass

Johnson et al., 1990; J Nutr 120:649Johnson et al., 1990; J Nutr 120:649

Liver weight increased 29 g per increase of 1 MJ of MELiver weight increased 29 g per increase of 1 MJ of ME


Effect of level of metabolizable energy Effect of level of metabolizable energy intake on gastrointestinal tract massintake on gastrointestinal tract mass

Johnson et al., 1990; J Nutr 120:649Johnson et al., 1990; J Nutr 120:649

GIT weight increased 61 g per increase of 1 MJ of MEGIT weight increased 61 g per increase of 1 MJ of ME


Maintenance Energy Requirements

• Maintenance energy requirement is directly related to vital organ mass

• Animals on high plane of nutrition have higher vital organ mass

• This principle is very important when shifting animals from high plane of nutrition to lower nutritional level.

Supplementation and Monitoring Nutritional Status of

Grazing Animals

Considerations for Supplementation

1. Will the supplement substitute or complement the forage intake?

2. Feed to meet protein needs and manage to meet energy needs

3. Feeding for breeding is the most economical4. Design the system to balance the cow’s annual energy

budget5. It is more economical to reduce energy demand than

to try to feed large amounts of energy feeds.6. Creep feed calves during last 45 days prior to weaning

only if part of preconditioning program

Molasses-urea vs Concentrated Protein (CP) (e.g., Cottonseed or Soybean Cubes)

1. Molasses is self-fed –CP is hand fed

2. Intake of molasses can only be controlled when there is not a large energy deficit

3. Molasses works best when there is an abundant supply of potentially digestible forage

4. Do not provide over 1/3 of CP requirement from urea

5. Hand feeding useful for checking and handling animals

Feeding Cottonseed Cubes

• Can feed amounts up to 0.3% of BW per day

• Can feed 1, 2, or 3 times per week with comparable results

• Feeding after main morning grazing period has less effect on grazing behavior

• On low quality forages (< 7% CP) will increase forage intake and digestibility

• Can give large increase in DOMI

Guidelines for using 20% breeder cubes

• Work best if fed daily in the PM with total amount not to exceed 0.3% of BW

• Skipping days and feeding larger amounts may reduce forage intake and digestibility

• Energy in the cube tends to substitute for energy in grazed forage which reduces net benefit to the animal

• Feeding daily can disrupt grazing patterns

Forero, et al. (1980) J. Anim. Sci. 50:532-538.Evaluation of slow-release urea for winter supplementation of lactating range cows.

• Natural protein was superior to both urea and SRU. • SRU was slightly superior to urea apparently because

of improved palatability and intake of the supplement.• The 20% CP supplement with urea and corn fed at

2.44 kg/head/day showed reduced performance compared to the soybean supplement fed at 1.22 kg/head/day.

• Protein supplementation increased forage intake with the greatest increase from natural protein.

• Natural protein increased DMD of diet but urea did not.• Urea as the sole source of N is not highly effective in

enhancing fiber digestion. Animo acids and peptides with NH3 are more effective.

Forage Intake and Digestibility:Effects of Supplements

• Forage CP of 6-7% is threshold for major effect of supplemental protein

• Starch in the diet has a negative effect on fiber digestion primarily through changing rumen pH and microbial populations.

• On low CP forages, starch digesting bacteria compete with cellulose digesting bacteria for NH3 in the rumen.

Monitoring Nutritional Status of Grazing Animals

• Vegetation

• Animal

• Feces

Integration of Procedures for evaluating nutritive status of range animals

1. Determine forage availability

2. Determine nutrient content of diet

3. Estimate nutrient requirements of animal

4. Determine nature and extent of nutritional deficiencies

5. Evaluate management practices to determine causes and possible solutions

Range SiteRange Site

Monitoring Vegetation‘Observational’

• Total amount available– Forage density and distribution– Potential bite size

• Nutritional heterogeneity– Live-dead– Leaf-stem– Species composition

Vegetation Analysis

• Measuring standing crop

• Chemical analyses– CP, TDN, IVOMD, minerals

Monitoring Animals

• Animal body condition score

• Animal weight

• Animal appearance– Fill, hair coat, eyes, ‘body language’

• Animal behavior– Grazing periods (start and end)

Feces

• Size of pats

• Shape of pats

• Moisture content of pats

Fecal ChemistryFecal Chemistry Bonds of:Bonds of:

Carbon Carbon

OxygenOxygen

NitrogenNitrogen

HydrogenHydrogen

Predicted DietPredicted Diet

Crude ProteinCrude Protein

Digestible Organic MatterDigestible Organic Matter

Diet QualityDiet Quality Crude ProteinCrude Protein

Dig. Org. MatterDig. Org. Matter

DIET:FECAL PAIRSDIET:FECAL PAIRS

-0.15

-0.1

-0.05

0

0.05

0.1

NIR Spectrum

==

++

Y = Y = β β 0 0 + + β β 1x1x + + εε

Diet quality as estimated by NIR analysis of fecal samplesDiet quality as estimated by NIR analysis of fecal samplesfrom Garfield Co, MT Rangelandfrom Garfield Co, MT Rangeland

1996-2001

44

55

66

77

88

99

1010

1111

1212

1313

% C

P%

CP

5454

5555

5656

5757

5858

5959

6060

6161

6262

6363

6464

% D

OM

% D

OM

CP

DOM

96 97 98 99 00 01

Summary – Systems Thinking

• Think holistically– Climate– Soils– Plants– Animals– Management

• Work to create synergy between parts of the system

Nutritional Considerations for Livestock on Rangelands Mort Kothmann Texas A&M University.

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Transcript of Nutritional Considerations for Livestock on Rangelands Mort Kothmann Texas A&M University.