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Effect of Feeding Cod Liver Oil and Unsaturated Fatty Acids on Rumen Volatile Fatty Acids and Milk Fat Content

Dairy Department, University of Maryland, College Park

ABSTRACT

The depressing effect on the fat content of milk induced by the feeding of cod liver oil to cows has been known since the early 1920's [see review by Hilditch (2)]. Hilditch has proposed that the unsaturated fatty acids of the C₂₀ and C₂₂ series are responsible for this depression, possibly by exerting a poisoning effect on mammary enzyme systems. Hydrogenation of the cod liver oil eliminates the effect.

In view of high correlations observed between the molar per cent of rumen acetic acid and fat content of milk, and an equally high negative correlation between the molar per cent of rumen propionic acid and fat content of milk (9), it appeared that cod liver oil might exert its effect on fat content of milk by altering the proportions of the rumen volatile fatty acids (VFA). Accordingly, the rumen VFA of six cows were determined before and after the initiation of the per os administration of 150 ml. each morning and evening of cod liver oil, oleic acid, or linoleic acid.

All cows had been on constant feeding regimens for over a month prior to the administration of these additives. Three of the cows had been on a normal diet and three had been on diets designed to decrease the fat content of milk (1, 7).