Who knows what the 2012 crop year will bring; wet, dry, both…. But we do know that high quality forage is the key to healthy productive cows. One way to maximize forage quality is to avoid or at least minimize butyric acid in hay crop silages. How best to achieve this?
As a research facility we’re occasionally asked to perform product testing of silage inoculants, some with claims of minimizing butyric acid production resulting from clostridial fermentations. To do this we need to be able to create butyric acid silage under controlled conditions to substantiate whether a product can prevent such fermentations. Eric Young and I were designing such a study and inquired with Limin Kung (University of Delaware) on how best to create butyric silage. In our research experience we had not been able to do so. Sometimes the best way to learn how to prevent something is to understand how to create it.
Limin indicated that creating butyric silage in a research setting is very difficult. Why then is it so easy in the field? In Limin’s experience, very wet silage does not necessarily result in butyric fermentations, nor does adding soil to forage. The one factor that did result in butyric acid was delayed chopping or rather prolonged wilting. Wet and dirt alone does not necessarily create butyric acid fermentations, but when combined with delayed harvest, it occurs.
Limin shared some data looking at various products where he ensiled 25-27% DM ryelage in minisilos, either immediately ensiled or delayed for 12 hours after chopping. All test product and control samples had similar pH of about 4.6, with varying levels of lactic and acetic acids, 0% butyric acid and 0.34% NH3 (ammonia) on a DM basis. Under the 12-hour delayed condition, pHs ranged from 5.82 – 6.42, butyric ranged from 0.12-0.22% with NH3 0.90 – 1.04% across treatments. Limin mentioned another study he conducted with alfalfa at less than 20% DM, where there was no butyric acid when immediately ensiled. After 12 hours delay in ensiling, butyric acid levels ranged from 2.05 – 3.13% of DM, NH3 ranged from 0.97 – 1.10% of DM and lactic acid was 0% across all treatments.
The key factor is that the water soluble carbohydrate (WSC) content of the forage is too low after prolonged or delayed wilting stage. WSC are the fuel of fermentation for the desirable lactic acid-forming bacteria. If WSC is too low, clostridia take over. They can break down protein, resulting in butyric acid and NH3. In the lab Limin had to allow the forage to sit overnight for about 12-16 hours before ensiling in order to obtain butyric acid. Plant cells continue to respire after the plant is mowed and chopped. The cells are burning off their WSC the very fuel that we need to properly ferment the forage. In the lab, immediate packing of chopped forage preserves sufficient WSC for proper fermentation. The delay allows for plant cellular respiration to consume the WSC, leaving no sugars for proper fermentation–only protein. In the field harvest delays often result from rain delaying harvest.
In terms of preventing butyric acid when faced with delayed harvest, Limin states that “Nothing Stops It.”
Take-home message to minimize the risk of butyric acid silage fermentation: Chop at proper DM% (32-35%), avoid soil contamination, and above all, avoid harvest delays. If faced with impending wet weather and delayed harvest, it may be better to chop on the wetter side when forage is fresh rather than waiting and losing all water-soluble carbohydrates needed to fuel a proper fermentation. Lastly, if possible, consider segregating high-risk forage rather than spreading throughout the pile or cut the loss and compost.