Interpreting Grass Silage Analysis

With grass silage still making a lot of rations silage analysis results are often overlooked as an important tool for ensuring that producers get the best from their silage. Producing quality silage not only helps drives production, it helps producers take control of their on farm costs especially when purchased feeds are expensive. Silage analysis can be used to help producers formulate the correct TMR diets for their particular on-farm needs and there are various laboratory methods used to calculate the chemical composition of silage, such as Near-Infrared Reflectance Spectroscopy (NIR) or wet chemistry. But no matter which method used the results produced need interpreting to understand their significance.

Dry matter. (DM)

Dry matter (DM) is the quantity of material left after the water has been removed from a silage sample. Grass silage is typically between harvested between 30-40 DM although this can change dependent of region.

Wetter forages grasses, can be low in sugar levels, making the ensiling process difficult. Also, wetter silage is the more prone to field contamination such as soil, which will negatively affect the ensiling process. Check the pH, ammonia and crude proteins contents if the grass silage is below 30% Higher than expected pH with reduced CP levels and high ammonia indicate that the silage has not ensiled quickly enough and the grass proteins are being broken down increasing the pH and ammonia content all of which means reduced silage quality.

Wetter grass silage need to be treated with products that are design to ensile grass quickly such as MAGNIVA Classic +

Higher DM grass silage are generally, more difficult to consolidate correctly.  The higher the DM the more difficult it us to remove all the air from the silo/bunker. This negatively impacts on the ensiling process slowing the pH drop making it easier for undesirable bacteria and yeast to grow, leading the silage to heat and spoil. If the grass silage you have is higher than 30% DM and the grass silage is heating or spoiling it indicates a slower than ideal ensiling process has occurred. Drier silage not only requires a quick preservation they need to be stable when opened for feedout. MAGNIVA Platinum 2 and MAGNIVA Platinum 3 are designed not only to preserve the grass quickly but inhibit the growth of yeast and molds reducing heating and spoilage


pH is the measurement on a scale of 1-14 of acidity or alkalinity of silage. Lower values, less than 4.5 indicate higher acidity levels which are required to preserve grass silage, especially wetter grasses. This helps retain as much of the original forage feed value as possible. If grass silage has a pH above 4.5 and is in the normal DM range, this suggests a less than ideal ensiling process occurred and the silage could be of lower quality and prone to heating and spoilage.

Digestibility. (D Value)

The D value is the quantity of digestible organic matter in the DM, measured as a percentage. The values vary as and when the grass is harvested. It tends to be higher earlier in the growing cycle and decrease over time as the grass matures. So harvesting the grass at  highest digestibility should be the aim of the producer if making high energy silage

Metabolizable Energy. (ME)

ME is important as its a measure of the total energy content of silage available to an animal when fed. The calculation is based on the D value and can  reported as Mega Joules/Kg (MJ/kg DM). The higher the value, the more energy the silage contains. Most grass silage should be between 10-12.5 ME but this is very much dependent of the D value and the quality of the preservation. Better preserved and ensiled grass silage will maintain ME, whilst poorly ensiled grass will see a reduction in the overall energy value.

Neutral detergent fiber (NDF)

NDF value is a measurement in percentage of the fiber fractions found in silage, such as hemicellulose, cellulose and lignin. NDF measurement is important as it’s linked to potential intakes, and although some fiber intake is essential to maintain rumen efficiency, too much can cause problems. NDF  digestibility decreases as a crop matures and intakes with higher NDF forages  decrease, as the fiber content in the rumen tends to increase. Some forage inoculants such as MAGNIVA Platinum 3 and MAGNIVA Classic + contain enzyme packages that are design to break open the some of the fiber structures, help to release sugars to aid the ensiling process and increase digestibility.

Crude protein (CP) %

This is a measurement of the total protein content in silage.  As the name suggests though, crude protein does not differentiate between grass proteins and external sources such as nitrogen fertilizer residuals etc. The higher the crude protein the more a forage is buffered, making the ensiling fermentation more difficult to achieve. Very high crude protein in grass silage (>16-18%) are an indication that the silage has suffered from late application of fertilizer.

Ammonia nitrogen (NH3)N –

(NH3)N is the measurement of the protein content in silage that has be been broken down to ammonia, through the ensiling process. Grass silages with a lower value, indicate that the preservation of the silage was good and the protein was protected through the ensiling process. Higher values such as more than >12% indicate a poor fermentation has occurred and proteins have been degraded to ammonia, lowering the overall feed value of the silage and quite possibly the palatability.

Lactic acid

The amount of lactic acid gives some indication to the quality of the fermentation. The amount of lactic acid required  is dependent on forage type and the dry matter harvested. Typical well-fermented grass silages have lactic acid contents of between 3 and 12 dependent on the DM of the grass ensiled. Using a crop and condition specific forage inoculant such MAGNIVA Classic or MAGNIVA Platinum 2/ MAGNIVA Platinum 3 can ensure enough lactic acid is produced quickly to ensure the grass is ensiled efficiently.


The total mineral content of the silage.  This represents the forage mineral content but also the ‘hygienic status’ of the silage (amount of soil ensiled). As the Ash content rises, fermentation challenge is increased, as well as associated feed losses. As a general rule the ash content in silage should be less than 10%. Just 1 gram of soil can contain up to 10 billion bacteria and although not all will be undesirable it makes the ensiling process more difficult to achieve

 Water Soluble Carbohydrate (WSC)

The amount of sugar available for the  fermentation if measuring fresh forage or the amount left after the fermentation is completed (fermentation acids are produced from WSC). If the grass silage to be ensiled is lower in WSC is could be necessary to use an inoculant which contains an enzyme package, design to release sugar to help with the ensiling process. Inoculants such MAGNIVA Classic + and MAGNIVA Platinum 3 are two such inoculants




Read what your silage analysis tells you about your wholecrop cereal silage.


Lallemand Animal Nutrition does not purport, in this guide or in any other publication, to specify minimum safety or legal standards or to address all of the compliance requirements, risks, or safety problems associated with working on or around farms. This guide is intended to serve only as a beginning point for information and should not be construed as containing all the necessary compliance, safety, or warning information, nor should it be construed as representing the policy of Lallemand Animal Nutrition. No warranty, guarantee, or representation is made by Lallemand Animal Nutrition as to the accuracy or sufficiency of the information and guidelines contained herein, and Lallemand Animal Nutrition assumes no liability or responsibility in connection therewith. It is the responsibility of the users of this guide to consult and comply with pertinent local, state, and federal laws, regulations, and safety standards.

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