Buffer Requirements for Maintenance of pH during Fermentation of Individual Feeds in Continuous Cultures

Continuous culture fermentations were conducted to determine the base requirement of eight individual grains and five forages. Feeds varied widely in the amounts of base required, from —.64 to 3.12 eq base/kg dry matter, to maintain pH at 6.5 during fermentation. Base requirements of four mixtures of feeds were 1.28, 1.27, 1.72, and 1.30 eq/kg for a corn silage + grain mix, hay crop silage + grain mix, corn + soybean meal mix, and alfalfa + corn mix. Base requirements predicted for these mixes from weighted base requirements of each component agreed fairly well with actual requirements. Base requirements of individual feeds then were related to feed analyses by stepwise regressions. Crude protein and acid detergent fiber contents of feeds were most closely correlated with base requirements and predictions from the regression equation were 1.14, 1.20, 1.76, and 1.33 for the four mixes. Prediction of base requirements was not improved by including fermentation data. Crude protein and acid detergent fiber may be useful for predicting buffer requirements of forage-grain diets; however, the relationship between these in vitro results and in vivo response requires further evaluation.