Evaluation of Silages: What a Feed Test Means

Written by Dan Loy, Ph.D., Professor, Iowa State University, Director of the Iowa Beef Center

There a few factors that are important as producers start to look at the key features in a lab analysis that might be important to help them make decisions about how to use silages in a particular diet and the value of those silages.

There are four key factors:

  1. Nutritional value of silages and how they can be used to balance silages with other feedstuffs
  2. Proper fermentation, which indicates the quality of the fermentation — or the lack of quality of fermentation and how that might be compensated for
  3. Proper storage and feed out characteristics
  4. Yield data to evaluate the economic value of the silages

First, dry matter (DM) is very important because silage is a high moisture feedstuff, and DM will eventually vary. DM tests can be done frequently with simple tests like those performed in a microwave. For more accurate results, it can be mailed in with other nutritional analysis as well.

The second part is chemical composition. A lot of what we’re doing with this analysis is evaluating the fiber profile and the carbohydrate profile to estimate the energy value of the silage. Fiber is measured by neutral detergent fiber (NDF), which is all of the cell walls in the plant itself. NDF is related to the feed intake and is important for normal rumen function.

Fiber is also measured by acid detergent fiber (ADF) values, which is fiber that is not soluble in an acid detergent. ADF includes cellulose, which is partially digestible, and lignin, which is not digestible. These measurements are correlated to the energy value, or total digestible nutrients (TDN), of forages. A lot of times the energy value is estimated based on the ADF. Energy values also can be measured through a process called in vitro digestibility. In a laboratory, the feed sample will be digested using rumen fluid from an actual animal.

Fermentation profiles look at how well the fermentation process happened. One of the key factors is the pH. Typically, we’d like to see the pH around 4. We’d also like to see a good production of lactic acid, less production of acetic and ideally no butyric acid. If we can get that combination, usually we have a good fermentation. This is indicative not only of nutritional value but also indicates minimal storage losses. We also look for quality factors like yeast and mold counts.

For finishing cattle, silage is a roughage source. Therefore, particle size is important. We can evaluate particle size with a particle separator.

Finally, sample preparation is important. Samples can be degraded in route. Be sure to follow the provided instructions for getting samples to the laboratory.

To hear Dr. Loy’s full presentation, visit http://beef.unl.edu/silage-beef-cattle-conference to watch the video, listen to a summary or read the 2016 Husker Corn Silage Conference proceedings. The conference was sponsored by Lallemand Animal Nutrition, the University of Nebraska Extension and the Iowa Beef Center.


Sponsored by Lallemand Animal Nutrition



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