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

Abstract

The molar composition of the rumen volatile fatty acids was studied at 3 dietary ratios of hay to concentrate in 12 dairy cows used in a lactation-balance experiment previously reported.The relative proportion of acetic acid decreased and that of propionic and butyric acids increased with increasing proportions of concentrate in the ration. The efficiency with which digestible energy was utilized for milk production was highly correlated with the molar percentage o*f propionic acid, 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 implications of a causal relationship are discussed.