Relationship of Certain Milk Fat Depressing Diets to Changes in the Proportions of the Volatile Fatty Acids Produced in the Rumen

Abstract

Summary Twelve high-producing Holstein cows were used to study the effect of feeding cod liver oil and a high-grain restricted roughage ration on milk and fat production, fatty acid composition of the milk fat, and the proportions of volatile fatty acids in the rumen. The cod liver oil and high-grain rations did not significantly alter milk production when compared to a control diet; however, these rations did significantly lower the fat content of the milk produced. When cod liver oil was added to a normal ration of hay and grain, the proportions of the volatile fatty acids in the rumen were unaltered; whereas, the high-grain diet caused a significant decrease in the proportion of acetate and a significant increase in propionate. As a result of these findings, it was concluded that cod liver oil exerts its effect on milk fat production somewhere beyond the rumen, whereas the fat depressing effect of high-grain feeding must be attributed to the significant changes occurring in the rumen fermentation.