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Corn Silage Quality Measurements

Dairy Pipeline: August 2000

Charles C. Stallings
Extension Dairy Scientist, Nutrition
Virginia Tech
(540) 231-4758

Most dairymen know that typical corn silage will range in protein from 7 to 8% of the dry matter and net energy from .66 to .72 Mcal/lb. (depending on the lab making the analysis). These measurements do not always give a complete picture of the feeding value of the silage, however. The type and amount of acids produced during storage can give an idea of the adequacy of the fermentation. Ammonia nitrogen content can give an idea if excessive protein is broken down during storage. Yeast and molds can indicate adverse biological processes that can lead to poor quality silage. Below is a fermentation profile of well-fermented corn silage.

Lactic acid4-6% of dry matter
Acetic acidless than 2%
Butyric acidless than .1%
Propionic acidless than .5%
Ethanolless than .5%
Ammonia nitrogen           less than 5% of total nitrogen
Yeast and moldsless than 100,000 colony forming units/gram

Note that the pH needs to be below 4.0 for the silage to be stable. The dominant acid should be lactic. If other acids such as acetic, butyric, or propionic become more predominate this indicates a shift in the profile that can result in poorer quality silage that may not be as palatable to the cows. Ethanol fermentation should be avoided. Also high levels of ammonia are indicative of excessive proteolysis of proteins. These measures can be an aid in problem solving situations but are probably not warranted on a routine basis. They do give one more measure of the quality of the silage.

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