Relationship of Milk Production Efficiency to the Relative Proportions of the Rumen Volatile Fatty Acids

The molar composition of the rumen VFA was studied at three dietary ratios of hay to concentrate in 12 dairy cows used in a lactation-balance experiment previously reported.As the proportion of concentrate in the ration increased, the relative proportion of acetic acid decreased, whereas that of propionic and butyric acids increased.Correlation analyses indicated that the efficiency with which digestible energy was converted to FCM was highly correlated with the relative proportion of propionie acid in the rmnen VFA and with the ratio of acetate to propionate, as well as with the crude fiber content of the ration.The plausibility and some of the i,,pli<.ations of a causal relationship are discussed.