Influence of Acetic Acid, Lactic Acid and Ethanol on the Fermentation of Corn Silage

The function of end products of silage fermentation, added initially at levels commonly present in fermented forage, in directing or limiting fermentative activity was evaluated using Plexiglas laboratory silos. Additions, on a dry matter basis, included .7% ethanol, .9% acetic acid and 4.7% lactic acid to chopped corn plant material, singly and in all combinations in a 23 factorial arrangement of treatments using 24 laboratory silos with three silos/treatment. Lactic acid added singly stimulated nonlactic acid fermentation. It increased gas production, wet matter loss, energy loss and ethanol levels to values that were 1.6-, 1.3-, and 2.2-fold those found in untreated silage. Lactic acid caused a 41% reduction in acetic acid production. Final lactic acid levels were elevated slightly and pH was reduced. Acetic acid alone inhibited fermentation, since it decreased production of lactic acid and ethanol by 18 and 30% and reduced wet matter and energy losses by 18 and 67%. Ethanol added independently increased lactic acid production 25%, reduced energy loss 52%, but did not alter acetic acid or ethanol production since the resulting silage ethanol levels were elevated to the extent of the initial addition. Responses to combinations did not parallel independent additions. The combination of acetic and lactic acids essentially eliminated their production, since final levels were about equal to the amounts added and reduced gas production to 35% of that from control silos. In this treatment acetic acid negated in part the stimulatory effect of lactic acid on ethanol production, reduced wet matter loss as occurred with acetic alone and resulted in an energy loss that was similar to that for control silos. Other combinations appeared to result in unfavorable responses. Lactic acid added with ethanol reduced production of lactic and acetic acids, increased energy losses and elevated both gas and ethanol productions. While acetic acid or ethanol added independently reduced energy losses, when used in combination energy loss was similar to controls. The combination of lactic and acetic acids with ethanol reduced production of gas, but energy losses were about twice those for control silos. Regulation of fermentation via acetic acid, ethanol and lactic acid was only indirectly related to pH suggesting selective microbial action of these end products on fermentation processes.