Upon opening the silo, and more often than desired, we come face to face with our worst fears. Although little can be done at this point, it is imperative we take the time to evaluate the whys and hows to reduce the chance of repeating our mistakes.

The following is a list of symptoms for common 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-producing bacteria dominate the environment, converting 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)
This condition typically occurs when the bunker is filled too slowly or packed too lightly so that oxygen is not excluded. It also occurs when there is inadequate feedout (large surface area of the silo), low silage moisture in a mature crop, chop length that is too long or unrepaired ruptures in the silage covering.

3. Heat damage (dark brown to black color)
This is an indicator of high temperature damage most likely caused by improper exclusion of oxygen. The dark color and strong burnt caramel or tobacco smell may be caused by improper compacting, incorrect stage of maturity (too mature), long chop length 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, increasing the pH of the silage. This problem is usually accompanied by extensive mold growth and spoilage. It is 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-risk spoilage organism populations (such as yeast and mold), 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 feedbunk 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, long particle size, low crop moisture and inadequate 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 the following conditions are met:

•fill the silo as fast as possible, therefore minimizing exposure to oxygen
•make sure cutting knives are sharp and the cutting length is correct
•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.  PD

—From Utah State University Extension Dairy Newsletter, Vol. 29, No. 2

Dr. Duarte Diaz, Extension Dairy Specialist, Utah State University

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