Ministry ofAgricultureand Food

ORDER NO. 79·049

MAY 1979

120AGDEX 52

QUALITY HAY CROP SILAGE(Replaces Factsheet "Heat Damage in Hay-Crop Silage, " January 1976)

S.G. Cressman, Live Stock Branch, B.D. McKersie and R.J. McLaughlin, Department of Crop Science,Ontario Agricultural College, University of Guelph

portance of covering horizontal silos to avoid excessivedry matter losses often associated with this silagesystem.

Heating DamageSilage losses can be measured in terms of quantity

(weight loss) and quality (feeding value). The fact thatsome silages may experience little dry matter loss does

DRy MATTER lOSS

Figure I. Estimated field, harvest and storage loss

Courtesy: Heath, M.E., D.S. Metcalfe and R.E.Barnes, Forages, 3rd ed., Iowa State University Press,Ames, Iowa. 1973.

TrenCh or Bunker 80'~:~~CSilos, Covered 70_

40

_ F.eld lo!>!>

~ seepo,.e lo!>!>

~ Go!>eov!> Loss

c:::J Surface Spoila,.e

302010

70~

60a50

40

80§70

656050

STOCk Silos 80No Covers 70

Stock SLlos 80Covered 70

0

Trench or Bunker 80~~~~~~Silos, No Covers 70_

Towe' SLios

ConvenTional

SilO-TYPE MOISTURE %

GasTIQhT

Tower $llos

The greatest amount of high quality protein andavailable energy in forage can be preserved by un­derstanding and managing both harvest and storagelosses. The degree of these two losses is primarily af­fected by the dry matter content of the forage. Wiltingto higher dry matter levels results in higher harvestlosses but lower storage losses (Figure I). Field curedhay has the highest harvest loss but lowest storage loss.On the other extreme, direct cut silage has the lowestharvest loss and highest storage loss. Farmers generallyswitch from hay to hay silage to reduce in-field dryingtime, thus reducing or avoiding costly weather damage.However, it is important for a farmer to consider bothfield losses and storage losses when choosing the correctsilage system for his operation.

Five types of storage losses are associated with silagesystems. Respiration losses occur when plant cellscontinue to breakdown carbohydrates and sugars due toexcessive amounts of air present in the silage. Fer­mentation losses result from excessive breakdown ofsugars by yeasts and molds contained on the plantmaterial. The main breakdown product of both theselosses is carbon dioxide along with water and heat.Seepage losses result when excessively wet silagecompresses the silage mass forcing moisture out of thesilo. This seepage carries carbohydrates and othernutrients with it. Surface spoilage is another loss whichoccurs when the less compacted silage in the upperportion of the silo is exposed to air. Finally, there is heatdamage which is mainly a quality problem with dryersilages reducing protein availability.

Figure 2 shows the types and degrees of both field andstorage losses associated with various silage systems. Itshould be noted that measuring all such losses is dif­ficult and the figures shown do not reflect all situations.Research at the University of Wisconsin found anaverage of 9"70 dry matter loss in concrete silos filledwith alfalfa-grass hay silage. Oxygen limiting siloscontaining similar material suffered 70/0 dry matterlosses indicating that with proper management, lossescan be held to nearly the same level in concrete towersilos as in oxygen limiting silos. Other tests and fieldexperience have indicated that it is possible to makegood quality silage in a horizontal silo, but only withexcellent management. Figure 2 indicates the im-

Table 1. Protein digestibility ("70) as affected by tem­perature and length of storage

MOISTURE PERCENT WHEN HARVESTED

Figure 2. Field and storage loss with various silagesystems

Courtesy: Heath, M.E., D.S. Metcalfe and R.E.Barnes, Forages, 3rd ed., Iowa State University Press,Ames, Iowa. 1973.

Management PracticesThere are a number of management practices that are

important in the production of high quality hay cropsilage. Producers aiming for a 20% protein packageshould give serious consideration to the following:

I. Proper attention to forage species selection Purelegume stands will produce far more protein thanlegume·grass or pure grass stands. Percent protein inthe grasses is only about half of that found in thelegumes. Sowing a grass with a legume will dilute theprotein percentage of the stand and greatly reducethe quality of the harvested product. Alfalfaproduces more protein per hectare than any othercrop grown, including soybeans. It is by far thehighest yielding of the perennial forage legumes andshould be the species of choice wherever it can begrown.

2. Harvest at the proper stage of maturity Legumessuch as alfalfa, trefoil, and clover should be har­vested in the early bloom stage; grasses in the early

maximum for the particular temperature level attained.The reaction appears to start at approximately 40°C(100°F).

Heat damage is measured in laboratory analysis usingthe acid detergent fiber - nitrogen (ADF-N) test. Whenthe nitrogen content measured using ADF-N is above0.29% on a dry matter basis, the sample may be con­sidered heat damaged. The protein digestibility of thesesamples is 60% or less, whereas excellent quality silagesshould have protein digestibilities in excess of 65% .

Farmers have recently tended to store silage at lowermoisture contents than in the past. Following are someof the reasons for suspecting that lower moisture silagesare more susceptible to heat damage than highermoisture silages if excessive air exposure is permitted:I. The fermentation process in silage results in a

decrease in silage pH and utilizes water solublecarbohydrates in the reactions. Thus the morecomplete the fermentation, the fewer soluble car­bohydrates there are remaining to participate in thebrowning reaction. Since the amount of fer­mentation decreases with decreasing moisturecontent of the silage, it would appear that silagesmay increase in susceptibility to "browning" asmoisture content decreases. It has also beensuggested that the extent of the browning reactionincreases with higher pH (higher pH occurs whensilage is drier and ferments less) although the rate ofthe reaction may be slower.

2. Drier silages do not consolidate as well as wettersilages. Therefore drier silages have decreasedresistance to air infiltration and the probability ofheating is increased.

3. The specific heat' of silage decreases as the moisturecontent decreases. Therefore a given amount of heatproduced will increase the temperature of a driersilage more than a wetter one, and more damage willoccur.

40506070

E:,-<··} Storoo. Lon

~ Fi,ld ( Harvest Lon

BO

Healing period 43°C 51°C 7Ioe(days) tItO°F) (135°F) (160°F)

o(control) 69.7 69.7 69.73 68.7 65.8 60.29 68.4 64.4 50.0

18 65.2 58.6 35.830 65.4 49.0 30.1

not necessarily mean there is no great loss in feedingvalue. For example, heating of the silage causes areduction in protein digestibility through a processknown as "browning" or the Maillard reaction.

Silage fermentation, involving the production oflactic acid plus lesser amounts of other compounds,produces very little heat. For silage to heat air must bepresent in the silage mass. Heating in silage during thefirst few days following harvest is caused by: (I) plantrespiration; and (2) yeast and mold activity. Later in thestorage period, heating is related to yeast and moldactivity only. Minimizing air exposure is the key to theproduction of good quality silage.

Heating results in a "toasting" effect on the silagewhich darkens the color. The darkening color, orbrowning, is caused by the combination of part of thesilage carbohydrate with part of the silage protein toform a brown undigestible compound similar to lignin.Thus, protein tied up by the browning reaction isrelatively unavailable to livestock.

Laboratory experiments indicate that high tem­perature storage reduces the protein digestibility ofsilage (Table I). The browning reaction also increaseswith the length of the heating period. Since silage isstored for relatively long periods under farm conditions,the browning reaction would proceed towards its

50

'"'"0--' 40

0:

"'....\i 30

'">-0:0

....Z

"'U0:

"'0.

Datafrom: D. W. Gallagher. Heat Damage in Hay-cropSilage. M.Sc. Thesis, /976. University ofGuelph.

'Specific heat - the amount of heat required to raise /gram of material/ 0c.

Average Analysis (Dry matter basis»

"Actual Analysis of field samples submitted toUniversity ofGuelph Feed Lab during /977/78

3. Keep hay silage away from dry dairy cows wherehigh intakes of calcium have been found to result inincreased incidence of milk fever. For details seeOMAF Factsheet Feeding and Managing Dry Cows,Order No. 79-029.

Legumehay cropsilage 42 48.62 18.51 1.48 .27 59

Cornsilage 1181 34.46 8.63 .24 .24 67

CrudePrOlein Calcium Phosphorus TON

070 11/0 flJo OJo

DryMatter

'10

Numberor

Samples

Feeding GuidelinesI. Collect a composite sample of silage for feed analysis

as the silo is being filled. Take a handful from everythird or fourth wagonload and place in a greengarbage bag. Mix the contents at the end of the dayand freeze a subsample sealed in a freezer bag. Afterthe silo is full, the samples should be thawed, mixedand a subsample submitted for feed analysis. If adigestible protein analysis is desired, then a sampleshould be collected after the ensiling process hasbeen completed and the silo has been open and fedfrom for at least two weeks.

2. Balance a feeding program for dairy cattle or beefcattle around the feed analysis results. Either theDairy Ration Formulation Service or the BeefFinishing Program can be of assistance in developinga balanced ration which makes optimum use of theprotein contained in the hay silage. Note that haysilage is a good source of crude protein and calciumwhen compared to corn silage.

supply weight for compaction. Forage in the upperone-third of the silo should contain 65 to 70%moisture in order to get a better pack. In air-tightsilos the door should be closed as soon as silo fillingis complete. In conventional tower silos the forageshould be levelled and sealed with plastic if the silageis not to be fed out immediately. Sealing with plasticis essential on horizontal silos. The plastic should beadequately secured and weighted down. I f allowed toflop, the plastic cover can act like a bellows byforcing air into the silage mass.

9. Analyze for heat damage Dairymen having a feedanalysis done should request the acid detergent fiber­nitrogen (ADF-N) test to determine proteindigestibility. Color and odor of the silage are notgood indicators of protein digestibility unless thesilage is extremely dark andlor has a burnt odor.Any indication of browning of the silage or burntodors should be checked by a digestibility test.

stage of heading. Forages harvested in the earlystages of growth are higher in protein and energyvalue and are more palatable. With grass-legumemixtures harvesting should be done to correspondwith the proper stage of maturity of the legume,since this is where most of the quality is found.

3. Use the proper length of cut Fine chopping helps toexclude air because packing is tighter. A 'I, to '/,­inch cut is desirable with 65"70 moisture silage andabsolutely necessary with haylage containing lessthan 60% moisture. The correct chop is necessary forboth conventional and sealed tower silos. Air willpenetrate the haylage mass in sealed towers when thefilling port is left open or when the unloading door isopened for feeding. Length of cut and its influenceon packing is probably most critical for horizontalsilos. Harvester blades must be sharp and setcorrectly. Ledgerbars must not be worn badly.Chopping finer than a quarter inch is not necessaryand undesirable since it is often a contributing factorto depressed butterfat test.

4. Maintain the proper moisture content Alfalfa willretain 70% moisture (30% DM) without seepage atnormal silo pressures. To allow for a safe operatingrange, start filling when the forage has wilted toabout 70% moisture. Later loads will be drier.Haylage usually contains 45 to 65% moisture.However, by waiting until 55% moisture beforefilling, much of the forage will be too dry to insuregood packing and the risk of heat damage will begreat. If the material becomes too dry, cut freshforage and continue to fill the silo by alternating dryand wet loads. Moisture contents generally need tobe higher for horizontal silos in order to get goodcompaction.

5. Provide a tight silo The walls and doors of new silosare usually air-tight. However, older silos may haveair leaks in the walls or around the doors. Theseshould be reconditioned andlor caulked and sealed.The silo acts like a chimney. If air can get in near thebottom it will be funnelled right up through thesilage mass. This could in turn lead to excessiveheating and spoilage.

6. Distribute evenly in the silo Even distribution in thesilo is necessary to avoid separation of the light fromheavier material by the silage blower. Light materialtends to land next to the wall, which leads to poorpacking and easy air penetration. If the wall happensto leak air, or when the feeding door is opened inbottom-unloading silos, a chimney effect isproduced.

7. Fill the silo rapidly continuously if possibleCompaction of the forage depends on considerableheight of material to provide the weight necessary toexpress air from the mass. Therefore, the upperportion will tend to be less dense and hold more airwhich causes heating. If filling is delayed overseveral days, the upper layer for each filling will benoticeably different in quality. Sealing the siloduring down time will help to reduce this effect.

8. Seal the silo Sufficient moisture is necessary to