Evaluating Silage Quality
Obtaining Samples for Quality Examination
It is extremely important that a representative sample of silage be obtained for quality determinations. How useful the analysis of silage will be is determined in large measure by analysis of silage as a whole. It how well the sample taken represents the silage is of little value to do quality evaluation of a silage sample that does not represent the silage being fed.
Forage samples for analysis should be taken as the silo is being filled. Sample each field and crop type separately. Take small sample of each load brought to the silo. As soon as possible after a load is sampled the forage should be placed in an airtight container and in a cool place such as a refrigerator or freezer. Individual samples from one field or crop type should be well mixed and a subsample taken for analysis. Enough forage to fill a container the size of a bread bag is more than adequate for laboratory analyses. The container used should be sealed to avoid moisture loss and frozen until it is submitted or mailed to a laboratory.
Avoid shipping or mailing samples at times when mail delivery may be delayed, such as close to weekends or holidays, since fresh forage samples deteriorate rapidly under warm conditions. Send the forage samples to the laboratory near harvest time rather than waiting until just before feeding or until other samples are available. All laboratories receive very large increases in sample numbers in the fall and early winter; this may result in delays if you submit your samples during that time period.
If samples have not been taken at the time of harvest, take samples as the silage is being removed from the silo. Take care to get individual samples from as many sites as possible from the face of the exposed silage and then combine them into one sample for analysis. It is also important that these samples be taken as soon as possible after the surface of the silage is exposed. When sampling upright silos, combine individual samples taken over several days.
Visual Evaluation
By itself visual examination will not provide accurate information on nutrient content of silage . However, coupled with a chemical analysis, factors such as color, odor and general appearance provide a good indication of the expected overall nutritive value. Characteristics which relate to nutritive value in grass and legume forages are listed below. The effect of the microbiological processes on the forage during ensiling needs to be evaluated, since even if the original material was of good quality the material may have ensued poorly. The following table provides some guidelines for assessing this aspect of silage quality.
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Chemical and Visual Characteristics of Grasses and Legumes | ||||
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Quality |
Stage of maturity |
Protein |
ADF2 |
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40-50% leaves, less than 5% foreign material such as straw and weeds |
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35-45% leaves in legumes, more than 50% leaves in grasses, less than 5-10% foreign material. |
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50% or more of legumes in bloom, boot to head stage in grasses |
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25-40% leaves in legumes, more than 40% foreign material leaves in grasses, less than 15% |
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Less than 30% leaves in legumes, grasses 30-40% leaves, or more than 10-15% foreign material. |
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More than 20% foreign matter in legumes, very mature forage, few leaves, etc. |
Chemical Analyses
Although silage quality can be estimated by visually examining the silage, it can only be estimated accurately by chemical analysis. The most important analyses obtained from feed testing laboratories include dry matter (moisture content is calculated as 100 minus percentage dry matter), pH, crude protein content, fibre, calcium and phosphorus. Analyses for other nutrients are also available.
Feed test reports can be evaluated in the same way for silages as they can for other forages. However, if the silage has heated too much, the digestibility of protein and dry matter may be greatly reduced. If heating temperatures in excess of 40°C) has occurred, as evidence d by a charred appearance or tobacco-like odor, it is useful to have the laboratory perform an acid detergent insoluble nitrogen analysis (ADIN). in general, if the acid detergent insoluble nitrogen content of a material is above 0.3 per cent of the dry matter or 15 per cent of the total nitrogen in the forage, it is indicative that excessive heating has occurred.
Silage pH as an indicator of quality
The best single indicator of the effect of ensiling on the nutritive value of high moisture silage is pH. The relationship between pH and silage quality can be determined using the following table. In general the lower the pH the better, since it indicates that a lactic acid type of fermentation has occurred. pH is, however, not a good indicator of quality for silages which contain less than 65 per cent water.
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Visual and pH Evaluations of Silage | ||||
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Good |
Intermediate |
Poor quality | |
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Poorly |
Overheated | |||
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Bright, light green-yellow or green brown depending upon material ensiled |
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Very dark green, blue green, grey, or brown |
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Lactic acid3 odor with no butyric4 acid odor4 |
Slight butyric acid and ammonia5 odor |
Strong butyric acid, ammonia, odor rancid |
Burnt sugar or tobacco smell |
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Firm, with softer material not easily rubbed from fibre |
Softer material can be separated from fibre |
Slimy, soft tissues easily rubbed from fibre, moldy |
Dry, easily broken down when rubbed, moldy |
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60-70% horizontal silos |
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Usually less than 55% Depends on type of structure |
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Below 4.2 for wet crops, below |
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pH is not a reliable guide |
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Too little moisture. Poor packing. Poor sealing. Length of cut too long, slow silo filling. |
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Poor fermentation may be corrected by ensiling at a lower moisture, using preservatives or sealing silo |
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Pack silage to exclude air, chop finer to facilitate packing, seal silage, ensile at a higher moisture. Fill silo rapidly and cover if delayed. |
2 pH can be determined with litmus paper which can be obtained from a pharmacist or use of pH meter.
3 Lactic acid odor is similar to that of sour milk.
4 Butyric acid odor is similar to that of rancid butter or fat, putrid.
5 Ammonia odor is similar to that in some household cleansers or anhydrous ammonia.
Fermentation Products in Silage
Normally commercial laboratories do not determine the concentrations of acids or ammonia in silage. However, if this information is available it is very useful. The table below gives some characteristics of different qualities of silages.
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Fermentation Products in Dry Matter and Silage Quality | |||
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Item |
Silage Quality | ||
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Good |
Intermediate |
Poor | |
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pH of silages with under 65% moisture |
Under 4.8 |
Under 5.2 |
Over 5.2 |
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pH of silages with over 65% moisture |
Under 4.2 |
Under 4.5 |
Over 4.8 |
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Lactic acid % |
3 - 14 |
Variable |
Variable |
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Butyric acid % |
Under 0.2 |
0.2 - 0.5 |
Over 0.5 |
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Proportion of total acids % |
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Lactic |
Over 60 |
40 - 60 |
Under 40 |
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Acetic |
Under 25 |
25 - 40 |
Over 40 |
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Butyric |
Under 5 |
5 – 10 |
Over 10 |
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Ammonia N (% of total N) |
Under 10 |
10 – 16 |
Over 16 |
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ADIN (% of total N) |
Under 15 |
15 - 30 |
Over 30 |
2 ADF - acid detergent fibre is a measure of the cellulose, lignin and cutin content of forages
* Published on the Government of Alberta Agriculture and Rural Development website
