A Symptomatic Look at our Silages
Dr. Duarte Diaz
USU Extension Dairy Specialist
One of the longest nights in dairying is the night before opening a new silo. Questions like: Did I get the moisture right? Did I pack tightly? Did I chop at correct length? are asked over and over until somehow we finally manage to fall asleep. Upon opening the silo, more often than desired we come face to face with our worst fears. Although little can be done at this point, it is imperative that we take the time to evaluate the whys and hows to reduce the chance of repeating our mistakes. The following is a list of common symptoms of problems in silages and the possible reasons for their occurrence.
1. Acetic acid smell (vinegar smell): this usually is a result of improper fermentation, when acetic acid bacteria dominate the environment and convert the available sugars into acetic acid. Ensiling a crop with high moisture content and low sugar content is the usual culprit. Lactic acid producing bacteria should dominate in silage fermentation;
2. Hot Silage (over 120�F): a condition that typically occurs when the bunker is filled too slowly, is packed too lightly so that oxygen is not excluded, there is inadequate feedout (large surface area of the silo), or there is low silage moisture in a mature crop, or chop length is too long, or when ruptures in the covering go unrepaired;
3. Heat-Damage (dark brown to black color): an indicator of high temperature damage most likely caused by improper exclusion of oxygen. This dark color and strong burnt caramel/tobacco smell may be caused by improper compacting, incorrect stage of maturity (too mature), long chop length, and/or low moisture content of the crop;
4. Spoiled milk odor (butyric acid): This strong off odor is typically caused by clostridial fermentation and the production of butyric acid. This type of fermentation occurs due to ensiling a crop at high moisture content and low sugar content (inadequate lactic acid bacteria for proper fermentation);
5. Alcohol smell: this smell is typically found in silages that have had fermentation dominated by yeasts, which convert the sugars into alcohol. These yeasts also utilize lactic acid, therefore affecting the pH of the silage (increased). This problem is usually accompanied by extensive mold growth and spoilage. Typical of poorly compacted silages made from overly dry crops;
6. Seepage (bunkers): excessive effluent (seepage or run-off) is caused by ensiling forages at higher than recommended moisture (i.e., low DM content). Damaging the plant tissue being harvested by utilizing dull chopper knives can also contribute to seepage problems;
7. Short bunklife: aerobic deterioration of silages during the feedout phase may be caused by multiple factors. Shortened bunklife may be caused by slow feedout (large surface area of the silo), high �spoilage� organism populations such as yeast and molds, low crop moisture at harvest, low plant sugars at harvest, ensiling the crop at an advanced maturity stage, or poor packaging (low packing density). Silage-based rations should not be left in the feed bunk for an extended period of time, especially in the summer months;
8. Moldy silage: the presence of oxygen due to improper packaging or slow fermentation are the main factors for promoting mold growth in silages. Slow feedouts, too long particle size, low crop moisture, inadequate or no covering are all favorable for mold growth.
The goal of any silage system is to start anaerobic fermentation as soon as possible, and to reach a pH below 5.0 as rapidly as possible. This can only be achieved when (1) we fill the silo as fast as possible, therefore minimizing exposure to oxygen; (2) we make sure cutting knives are sharp and the cutting length is correct; and (3) we ensile at the correct moisture content. Silage fermentation additives (inoculants) can be useful for achieving a quick and proper fermentation, but their effectiveness will also be dependent on the preparation and management of each silo.
Dr. Diaz may be contacted at (435) 797-2163 or Duarte.Diaz@usu.edu.