631. Variations in iodine value of milk fats

Abstract

Iodine values of milk fats of grazing cows show wide variations which are chiefly determined by differences in oleic acid content. Among the factors promoting the variations are: individuality of the cow, stage of lactation, breed differences, diurnal and incidental (irregular) day-to-day effects, nature of the food and plane of nutrition.Results of experiments with feeding an unsaturated vegetable oil indicate that considerable proportions of the unsaturated long chain acids of milk fat were derived from the ingested oil. It is deduced that herbage lipids may contribute materially to the production of milk fat of grazing cows.From comparisons of the extents to which dietary long chain unsaturated acids are incorporated into milk fats of grazing and semi-fasting cows, it would appear that the rise in iodine value following partial inanition does not result from increased uptake of fatty acids withdrawn from the more highly unsaturated glycerides of the body reserves.