The effect of certain ingested fatty oils upon the composition of cow milk fat

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Abstract
Detailed studies were made of the component acids in milk fats from cows receiving a normal winter ration and the same ration with additions of cod liver, linseed or rape oils. Cod liver oil had a marked effect, the lower saturated acids of the milk fats being reduced to half the normal content, while the proportion of oleic acid was much increased, and a certain amt. (5-7%) of highly-unsaturated C20-22 acids was present. Polyethenoid unsaturation in the C18 acids was not more than normal and palmitoleic acid had not been appreciably absorbed from the cod liver oil. The effect of linseed oil was merely to increase the proportion of oleic acid; linolenic acid was not detected in the milk fat and linoleic acid only in very small amts., the mean unsaturation of the C18 acids and the amt. of lower saturated acids were normal. Rape oil had a similar effect to linseed oil, but small amts. of erucic glycerides were present in the milk fats. The relationship between fully-saturated glycerine content and proportion of total saturated acids in the milk fats was normal (i.e. of the type characteristic of cow milk and depot fats) in all cases. The investigation shows that some of the highly-saturated C20-22 glycerides of cod liver oil (but not its palmitoleic acid or the linolenic and linoleic acids of linseed oil) pass into the milk fats; and it is suggested that selective adsorption of these highly-unsatu-rated compounds by the enzymes responsible for the elaboration of typical cow milk fats retards their normal function and causes the observed effects. This hypothesis is a corollary to that previously suggested to explain the abnormal production of fully-saturated glycerides in milk and certain animal depot fats, and is also in harmony with the results obtained on adding linseed, rape or shark liver oils to the diet of lactating cows.