Ministry ofAgricultureand Food

ORDER NO. 76-007

JANUARY 1976

AGDEX 12025

•HEAT DAMAGE IN HAY-CROP SILAGE

D.W. Gallagher, Food Land Development Branch andK.R. Stevenson, Department of Crop Science, University of Guelph

INTRODUCTION

The use of hay-crop silage is continuing to expand inOntario. With high-protein forages, farmers canminimize purchases of protein supplements. Sinceprotein content can vary markedly due to species andmaturity, producers are encouraged to have their storedfeed analyzed for protein content. The forage is normallytested for crude protein content which is assumed to be astandard percentage digestible. It has been known formany years however, that heating of the silage causes areduction in digestibility through a process known as"browning" or the Maillard reaction. Recently alaboratory test known as the acid-detergent fiber nitrogentest (ADF-N) has become available to test for reductionin protein digestibility by the "browning" reaction.

HEATING IN SILAGE

Silage fermentation, involving the production of lacticacid plus lesser amounts of other compounds, producesvery little heat. Similarly, wine does not heat when itferments.

Heating is caused by air exposure or by air entering thesilage mass. There is not enough trapped air in silage tocause serious heating. For silage to heat, oxygen must bepresent. Heating in silage during the first few daysfollowing harvest is caused by: (I) plant respiration and(2) yeast and mold activity. Later in the storage periodheating is related to yeast and mold activity only. Thus,essentially all heating is the result of the silage beingexposed excessively to air. Prolonged exposure results insilage spoilage.

Minimizing air exposure is the key to the production ofgood quality silage. Contrary to ideas prior to 1950, thereis no advantage to having warm or hot silage.

THE BROWNING REACTION

Heating results in a "toasting" effect on the silage whichdarkens the color. The darkening color, or browning, iscaused by the combination of part of the silagecarbohydrate with part of the silage protein to form abrown undigestible compound similar to lignin. Thus,protein tied up by the browning reaction is relativelyunavailable to livestock.

The browning reaction increases with the length of theheating period. Since silage is stored for relatively longperiods under farm conditions, the browning reactionwould proceed towards its maximum for the particular

temperature level attained. The reaction appears to startat approximately 40°C (100°F). An experiment wasconducted to determine the effect of temperature andstorage time on the reduction of protein digestibility.Good quality silage was placed in sealed containers andartificially heated. The results are shown in Table I.Dramatic reduction in digestibility occurred at hightemperatures.

Tahle I. Protein digestihility (%) as affected hytemperature and length of storage.

HeatingPeriod 43°C 57°C 7Ioe(days) (HO°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

Farmers have recently tended to store silage at lowermoisture contents than in the past. There are severalreasons for suspecting that lower moisture silages aremore susceptible to heat damage than higher moisturesilages if excessive air exposure is permitted.

(I) The fermentation process in silage results in adecrease in silage pH and utilizes water soluble car­bohydrates in the reactions. Thus the more complete thefermentation, the fewer soluble carbohydrates there areremaining to participate in the browning reaction. Sincethe amount of fermentation decreases with decreasingmoisture content of the silage, it would appear that silagesmay increase in susceptibility to "browning" as moisturecontent decreases. It has also been suggested that theextent of the browning reaction increases with higher pH(higher pH occurs when silage is drier and ferments less)although the rate of the reaction may be slower.

(2) Drier silages do not consolidate as well as weltersilages. Therefore drier silages have decreased resistanceto air infiltration into the silage 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 drier silagemore than a wetter one, and more damage will occur.

* SpeciJ;c heat - the amount ojheat required to raise 1gram of material I CO.

ONTARIO HAY-CROP SILAGES

One hundred and forty-six hay-erop silage sampleswere collected from Ontario farms in the fall of 1974 andwere tested for protein digestibility at the University ofGuelph.

Samples were collected at random from:

(I) steel glass-lined oxygen-limiting silos(2) concrete oxygen-limiting silos(3) stave concrete tower silos(4) poured concrete tower silos(5) horizontal silos

The results follow:

Crude Protein

The average crude protein content of all samples was13.8% with a range of 7.1 to 22.9%. Table 2 shows thenumber of samples in various ranges of protein content.These results indicate that improved feed quality could beobtained by more attention to timely barvesting andgrowing of the proper species of forages. Thirty sampleshad crude protein contents over 17.5%, indicating goodcrop management. The data indicated that owners of thedifferent silo types were placing equal emphasis on cropmanagement practices, since the average crude proteincontent was essentially the same for all silo types.

Table 2. Number of samples with crude protein contents in the ranges shown.

% Crude Protein(DM basis)

33 25

12.5 15to 15 to 17.5

Sample Origin

All Samples

Oxygen-limitingSteel glass-lined

Oxygen-limitingConcrete

Stave

east-in-place

Horizontal

7.5

4

7.5to 10

21

4

3

7

7

10to 12.5

33

9

14

7

3

17

I

3

8

4

7

6

9

3

17.5 20 TOTALto 20

23 7 146

7 3 48

2 I 5

5 2 33

5 I 38

4 22

RANGE: 7.1 to 22.9%MEAN: 13.8%

Table 3. Number of samples with protein digestibilityin the defined ranges shown.

moisture when put in conventional tower silos, andpreferably should be between 55 and 65% moisture. Driersilage can be stored in such silos but extreme care isrequired. Silage in oxygen-limiting silos should bebetween 40 to 50% moisture to facilitate unloading.

The moisture content distribution of the silage samplesin the survey is shown in Table 4. Clearly many farmersare putting relatively dry forage into conventional towersilos. Such a practice will be successful only under topmanagement.

Calculated Protein DigestibilityAbove 65% 60 to 65% less than 60%(excellent) (good) (heat

damaged)

5

I

7

8

I

4

8

5

8

4

28

24

9

35

SampleOrigin

Oxygen­limiting Steel

Oxygen­limitingConcrete

Stave

Cast-in-place

Horizontal

Moisture Content

In the present survey, protein digestibility had norelationship with moisture content. We believe it is stillunwise to place excessively dry material in conventionaltower silos and horizontals for the reasons mentionedearlier. Hay-erop silage should be more than 50%

Heat Damage

When the nitrogen content measured using the ADF­nitrogen test is above 0.29% (dm basis), the sample is saidto be heat damaged. In the survey, 17.1 % of the sampleswere heat damaged. An ADF-nitrogen value of 0.29%corresponds to a protein digestibility of about 60%. Forthe purposes of this Factsheet, samples above 60%protein digestibility will be considered to be of goodquality and samples below 60% protein digestibility willbe considered heat damaged. Excellent quality silageshould have protein digestibilities in excess of 65%. Thesummary of protein digestibilities from the varioustypes of silos is shown in Table 3. The average proteindigestibility was 64.3% with values ranging from 23.8 to78%. Regardless of silo type, the majority of silagesamples had protein digestibilities between 60 and 70%.The results indicated that top quality silage can be madein all types of silos providing proper management is used.However, under less than ideal management theprobability of heat damage is greater in conventionaltower silos and horizontals.

Table 4. Number of samples with moisture contents in the following ranges.

% Moisture

Sample Origin 20-29 30-39 40-49 50-59 60-69

All Samples 4 18 43 35 36

Oxygen-limitingSteel glass-lined 3 II 20 10 4

Oxygen-limiting 2 I 2

Stave 4 9 12 7

Cast-in-place 3 II 8 10

Horizontal I 4 13

RANGE: 23.9 to 85.0%MEAN: 52.5%

70-79

8

I

5

2

80-89

2

2

Total

146

48

5

33

38

22

Color and Odor

Dark color and burnt odor are general indicators ofheat damage. However, unless samples are black and! orhave a distinct burnt odor, these characteristics are notgood indicators of silage quality. If the silage is a darkerbrown than normal, or is black in color, a proteindigestibility test should be performed as outlined in thesection on sampling procedures.

Length of Cut

As length of cut increases, there is a tendency for lesscompaction to occur in silage, and therefore length of cutmay be an indicator of air infiltration and heating. Thedata indicated that good quality silage can be made withany length of cut providing proper management is used.The probability of incurring heat damage is probablygreater if the silage is cut very long (10 to 15 cm or 4 to 6inches).

SAMPLING PROCEDURES

Samples should not be taken until the silo has beenfilled for some time and fermentation is complete. Silageshould be mailed immediately after sampling or frozenfor later shipment, and should be shipped early in theweek to avoid delays over the weekend. If the silo has notbeen sealed with plastic sheeting, care should be taken toavoid areas that have been heat damaged at the surface byair infiltration. Further information on samplingprocedures as well as sample bags and cost informationare available from your county office of the OntarioMinistry of Agriculture and Food.

SILO MANAGEMENT

The practices required in storing good quality silage forlivestock are similar to those for preserving food forhumans. In preserving jam or fruit, a person starts with agood container, fills it quickly and seals it with a lid orlayer of wax until required. With such a procedure, goodquality food is usually obtained. In contrast, if a personfilled a jar of peaches over a period of 2 weeks by adding athin layer each day, and in addition, permitted the full jarto sit uncovered for several weeks, lower quality food islikely to result. Yet, the latter procedure is frequently usedin ensiling crops for livestock feed.

There are a number of practices which must be followedif good quality silage is to be made. First, the forage must

arrive at the silo in good quality. ]n addition, there are anumber of specific recommendations for silo manage­ment.

A. Oxygen-limiting silos

(I) Fill rapidly to minimize air exposure.

(2) Close hatches at night, weekends, and duringinterruptions in filling because of bad weather orbreakdowns. If hatches are left open during the wholefilling period, much of the possible advantages overconventional silos will be lost in reduced dry matter and inreduced heating. Research has shown that dry matterlosses can increase by at least 4% when the top hatch is leftopen at nights while filling. Leaving the hatch open forseveral days after silo filling is completed can causeserious red uction in feed quality.

B. Conventional Tower Silos

(I) Fill rapidly.

(2) If bad weather causes a stoppage in filling for severaldays, the silage should be covered with plastic.

(3) It is very important to cover the silage with plastic afterthe silo is filled. Hold the plastic in place with about 3inches of silage. The silage should remain covered for 5 to10 days before feeding. After this period, the plant cellswill no longer be respiring and the chances of seriousheating and dry matter losses will be greatly reduced. Forfarmers with two silos to fill, it is a good idea to fill andseal one silo, fill and seal the second and then start feedingout of the first.

If the above practices are followed during filling, and if2\1, to 3 inches are removed from the silo each day duringfeeding, the losses from the surface of the silage each daywill be very small. Research in the Crop ScienceDepartment indicates that losses are less than 0.1 % perday from surfaces of well-managed silos.

C. Horizontal Silos

A successful horizontal silo must look like a tower siloon its side when filling is completed. A farmer wouldnever build a tower silo with one side made ofconcrete orsteel and the other side of wire mesh to hold the materialin the silo. Clearly, excessive losses would result. Yet,many farmers still are unconvinced about the need to

cover horizontal silos and leave one side of the silo (thetop) open to air exposure.

(I) Rapid filling is critical.

(2) Filling the silo completely at one end and then movingtowards the other, filling the silo fully in the procedure, isbetter than adding layers to the whole silo daily.

(3) Cover with plastic. Hold the plastic firmly in place anddo not allow it to flop. The plastic does far more than justreduce surface spoilage. Well-laid plastic will improvesilage quality for several feet down into the silo.

CO CLUSIO S

(I) Generally Ontario farmers are producing hay-<:ropsilage with good protein quality.

(2) Proper attention to forage species selection and timelyharvest will increase protein content.

(3) Air infiltration must be responsible for any serious risein temperature of the silage. Therefore extreme care mustbe taken to stop air infiltration by packing to consolidatethe silage and by sealing with plastic. Any significantdelay in filling the silo may result in heat damage wherethe silage is in contact with air.

(4) Color and odor of the silage are not good indicators ofprotein digestibility unless the silage is extremely darkand/or has a burnt odor. Any indication of browning ofthe silage or burnt odors should be checked by adigestibility test.

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