Interpretation of Grass Silage Analysis

Importance of Silage Sampling and Analysis
Grass silage in the majority of cases will be the largest component of feed this winter. Grass silage is very variable, don’t make assumptions of the feeding value; test your silage. Any analysis is only as good as the sample received; and therefore makes sure you take a sample that is representative of your silage (or samples representative of your different silages).

Key point: Grass silage is likely to be a significant part of your animals’ diets this winter and is a very variable feedstuff. Getting a representative sample analysed is highly recommended.

What feeding value has your pit of silage?

Interpretation of Grass Silage Analysis
Once you receive your silage analysis report, what do you do with it? Your local ASM is available to discuss your silage sample results. However, this article should help in your own interpretation and understanding of what the terms and values on your silage analysis report(s) mean.  The following are evaluated and reported in the Dairygold silage analysis reports:
Dry Matter (DM)
Quantity of material remaining after all the water is removed, expressed as a percentage. The DM of a silage greatly influences its overall value as an animal feed. Most of Irish grass silages have a DM close to 20%.
• Bales tend to have higher DM% (typically circa 30%)
• Wet silages (less than 20% DM)
-Are more difficult to preserve
-Produce more effluent (higher losses)
-have reduced DM intake
• Livestock tend to eat more of higher DM silages but very high DM silages (more than 30% DM) are more difficult to consolidate which can lead to more of the silage spoiling.
Dry Matter Digestibility (DMD)
Key figure reflecting the feeding value of the silage expressed as a percentage.  High DMD silages will have high energy levels. Grass silages can have a huge range in DMD values from 45% to 85%!
• A DMD greater than 70% is desirable for milk production
• DMD values in the low 60s or below are poor silages and will struggle to even maintain animal live-weights if fed without supplementation

Recommended concentrate supplementation for dry cows at a BCS of 2.75 who will be dry for 10 weeks

This is the energy value of the silage for milk production or slow growing animals (<1Kg live-weight gain per day) using the Irish Net Energy system. 
• More accurate measure of energy than the old ME system.
• It is linked to DMD with 70% DMD silages equating to 0.79 UFL. 

This is the energy value of the silage for fast growing animals (>1Kg live-weight gain per day) using the Irish Net Energy system. 
• It is again linked to DMD with 70% DMD silages equating to 0.74 UFV. 

Key point: The feeding value of your silage can be determined by its DM% and energy levels (indicated by the DMD and UFL/UFV levels).

Neutral Detergent Fibre-a measure of the total fibre in the plant, which gives a guide to plant maturity-levels increase as grass matures and therefore high levels suggest stemy silage.

Measure of the acidity of the silage. 
• More acid (lower pH) is required to give storage stability to low DM silages.  If the pH is too high, it indicates poor preservation. 
• If the pH is too low it can reduce intake.
• The desirable pH range for clamp silage is shown in the table below.

Level of inorganic matter (mineral content) expressed as a percentage. Generally if the ash content exceeds 9% there is likely to be soil contamination of the silage.

Lactic Acid
The major acid in a well preserved silage is lactic acid.
• Badly preserved silage contains large amounts of other acids from secondary fermentation and low levels of lactic acid.
• The level of lactic acid in the silage depends on the sugar level of the grass at cutting, the degree of wilting, the quality of sealing and the preservation.
• Silages with a restricted fermentation will tend to have lower levels. However, higher levels are required with low dry matter silages that can make the silage very acidic and reduce intake.

Ammonia Nitrogen
Measure of the protein breakdown expressed as a percentage of the total nitrogen.  The level of Ammonia Nitrogen can be used as a partial guide to the success of the fermentation process. High levels (>10%) can indicate issues with preservation and values >15% can lead to reduced palatability with knock-on effects on intakes and animal performance.

Key point: How well preserved your silage is can be determined by its pH, lactic acid and ammonia nitrogen levels.

Crude protein
Traditional measure of protein based on nitrogen content of the silage.  Young, leafy grass tends to give higher proteins than older, stemy grass.

Young, leafy grass tends to give higher protein silages

A measure of protein quantity and quality.  Rumen undegradable or rumen by-pass true protein digested in the small intestine.

Microbial true protein made in the rumen from broken down dietary nitrogen plus by-pass protein (PDIA). 
• Closely tracks crude protein. 
• The PDI level of any feed is the lower of PDIN and PDIE. 
• Well balanced protein diets will have similar PDIN and PDIE levels.  In grass or grass silage based diets PDIN is usually significantly higher than PDIE (unless protein level is very low).
• Low PDIN silages require protein supplementation.

Microbial true protein made in the rumen from rumen available energy plus by-pass protein (PDIA). 
• DMD and UFL/UFV related to PDIE.
• Low PDIE silages require energy supplementation.

Key point: Crude protein is a poor measurement of the true protein value of your silage (and other feedstuffs). PDIN and PDIE give a better picture of the protein quality and its likely utilisation by your animals.

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