Fermentation and Preservation of Feed

Fermented feeds can be stored for years. The process of fermentation and preservation is nothing new to farmers and has been going on for thousands of years.

Fermentation and preservation happens in four stages—aerobic, anaerobic or fermentation, stable and feedout. Each of these stages results in feed that differs from its original form of fresh grass or alfalfa.

What follows is a brief description of what occurs during each of these four stages.

Stage One:

During the aerobic phase the grass or alfalfa is harvested and put into the silo. The plant, although cut, is still using some sugars. With oxygen present, changes still occur because there is air present. Fermentation cannot occur until there is no oxygen left. Microbes that live in these types of conditions will chew up the oxygen. The result of this stage is that the grass or alfalfa has less sugar than it did when it was fresh.

Stage Two:

This is a phase of active fermentation that occurs after the oxygen is gone. At this point, anaerobic bacteria and some yeast metabolize sugars and soluble carbohydrates into fermentation acids. This will cause the forage pH to drop until the environment is such that organisms are unable to grow. Since acetic and other acids are produced, carbon dioxide is generated and usable carbon is lost. Carbohydrates from the fresh feed are lost and reduced dry matter is the result. While there will be some nutrient loss, the feed is still preserved.

Stage Three:

During this stage the forage remains stable and fermented feed remains different from fresh grass and alfalfa. This occurs because enzymes produced by bacteria and fungi during the fermentation phase leak out of the dormant microbes and into the forage. These enzymes break down proteins and amino acids and create ammonia and other nonprotein nitrogen sources. The result is a higher soluble protein than the fresh grass or alfalfa. Dairy and feedlot cattle can use the nonprotein nitrogen because bacteria within the rumen rebuilds them into amino acids and proteins. Note that ammonia-nitrogen should be less than 10 percent of the total protein.

Stage Four:

During this stage the fermented forage is exposed to air. If stages one, two and three were carried out correctly, the feed will retain its nutritional value. Unfortunately, mold and yeast that went dormant during those stages could return. The results would be the loss of significant nutrients in this livestock feed. If there is substantial mold and yeast it could be detrimental to digestion of other ration ingredients. To prevent this from occurring, be sure to monitor and harvest forage at the ideal moisture range for your silo and work diligently to keep air out.

Fermented feeds can take a lot of work to produce but are well worth the effort. Especially in times when fresh forage inventories are threatened.