STINKY SILAGE

We’re hearing reports of heavy first cuts of alfalfa and alfalfa-grass. This combined with some cool, wet weather in late May resulted in some hay crops being ensiled before they were dry enough for proper fermentation. At 30% DM or lower there’s an increased chance of butyric acid produced by Clostridial bacteria. Manure application shortly before harvest further increases the risk of Clostridia spores contaminating the silage. Preventing butyric acid formation by ensiling at the proper DM is much better than trying to deal with stinky, low palatability silage.

The ideal amount of butyric acid in silage is none. However, concentrations of up to 0.5% shouldn’t result in livestock refusal or health problems, and the silage may not have an offensive odor. Lactic acid, the primary silage fermentation acid, is odorless while acetic acid is what gives properly fermented silage that vinegary odor. With 0.5% to 1.0% butyric acid there may be some animal refusal, while silage with levels over 1% is a serious problem, and it stinks. Literally.

In the bad old days when there was a lot of low DM forage ensiled (oat silage was a common offender), many farms had a hook outside the door of the house for the farmer to hang his coveralls since his wife wouldn’t allow that smell in her house. A fermentation analysis is the best way to evaluate silage fermentation, and it’s particularly important with low DM silages. Dairy One charges $38 for a fermentation analysis while Cumberland Valley Analytical Service charges $42, in either case money well-spent.

What’s worse than having silage containing a high concentration of butyric acid? Having a lot of it, in which case disposing of the silage isn’t a viable option. A fermentation analysis will include the percentage of butyric acid, which makes proper sampling essential. A rule of thumb is to feed no more than 50 grams of butyric acid per head per day to lactating cows. To calculate this, divide the percentage of butyric acid by 100 and multiply by the pounds of dry matter of this silage that you intend on feeding. Multiply this figure by 454 (there are 454 grams in a pound) to get the grams of butyric acid fed. Example: Butyric acid level of 1.6% /100 x 6 pounds of dry matter fed x 454 grams/pound = 44 grams of butyric acid fed per head per day. If the silage is 30% DM, 6 lbs. of DM is 20 pounds of as-fed silage. That may be somewhat less than you want to feed, but better safe than sorry.

Butyric acid is highly volatile, so one way to reduce the butyric acid concentration is to expose the silage to air for at least several hours before you feed it. This silage has good face life, so it shouldn’t heat in this amount of time. Remove the amount of silage you’ll feed tomorrow and let it sit overnight to allow some of the butyric acid to volatilize. (This has been done, and we’re told that it really works.) However, as Mom used to say: An ounce of prevention is worth a pound of cure, so it’s much better to prevent butyric acid by proper harvest management than to deal with the consequences of stinky silage.

— Ev Thomas

ethomas@oakpointny.com