Ensiled forages are the most common feeds used on the dairy farm. Silages are used primarily due to their potentially lower harvest and storage nutrient losses. Silages also allow for greater flexibility in moisture content of feed at harvest. This is primarily of importance in areas of the country where weather patterns do not allow for easy feed drying to make good hay.
The ensiling process is an anaerobic microbial fermentation of water-soluble sugars to lactic acid, lowering the pH to a point that inhibits further microbial fermentation. The goal is a rapid pH drop to minimize fermentation losses of feedstuff nutrients, especially protein. However, it must be remembered silage is never static. It is a potentially dynamic feed that can dramatically change for the worst given the right circumstances, such as the addition of oxygen.
Assessing Quality of Ensiled Feeds
Although silages are the most commonly used feeds, they are the most variable feeds on the farm. As a result, they are often the source of feeding-based problems. Based on the desired goals for high quality silage, we can use these parameters as critical measures of assessing silage quality. Like other feeds, quality can be assessed on three different levels: sensory evaluation, chemical composition and physical characteristics. Each of these methods of evaluation will be discussed with their interpretation relative to silage quality.
Sensory Evaluation of Silage
One can gain significant insight as to the quality of silage, corn or hay-crop, by its smell, sight and feel. Sensory evaluation may suggest the need for further chemical or physical characterization of the feed should a problem be identified. Sensory evaluation of silage would include the following:
- Observe the contour of the bunker face. Ideally the face should be very smooth and straight. This minimizes oxygen exposure to the silage. Bunker silos with irregular and uneven faces have greater surface area exposed to oxygen and thus a greater chance at increased microbial activity. As silage is reintroduced to air, mold and bacterial spores present in the silage can begin their metabolism again. This metabolic activity will result in silage heating as well as alterations in acids and sugars available in the feed. This metabolic activity suggests unstable silage and can contribute to depressed feed intake and feed refusals. This secondary heating is usually not sufficient to cause significant heat damage to the silage. The true value of bunk face management is not well known and is related to the density of the silage, the season of the year, and the amount of silage face removed each day.
- Silage color can indicate potential fermentation problems. Silages with excessive acetic acid will have a yellowish hue, while those with high butyrate will have a slimy, greenish color. Brown to black silage usually indicates heating from fermentation and moisture damage. These silages have the highest potential for molding and are unacceptable feeds. White coloration of silage is usually indicative of secondary mold growth.
- Silage odors can also be used to evaluate fermentation. Normal silage has minimal odor due to lactic acid. If acetic acid production is high, then silage may have a vinegar smell. High ethanol content from yeast fermentation may impart an alcohol odor to silage. Clostridial fermentation results in a rancid butter smell. Propionic acid fermentation results in a sharp, sweet smell and taste. Heat-damaged silages will have a caramelized or tobacco smell. No silage should have a musty, mildew or rotten smell due to molding. Remember if the silage smell is noticeably unpleasant to you, most likely it will be refused by the cow or cause reduced intake.
To learn more about silage evaluation and feed management, click here.
Originally published on February 15, 2016.
Photo courtesy of Penn State University.
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