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

Department of Animal Husbandry, Cornell University, Ithaca, N. Y.

ABSTRACT

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 propionic acid in the rumen 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 implications of a causal relationship are discussed.

¹ Present address: Department of Dairy and Animal Science, University of Massachusetts, Amherst.