The effects of intravenous infusions of cod-liver and soya-bean oils on the secretion of milk fat in the cow

Abstract

1. The effects of intravenous infusions of emulsified cod-liver oil, Ethive (British Codliver Oils (Hull & Grimsby) Ltd; ethyl ester fraction of cod-liver oil rich in polyunsaturated acids) and soya-bean oil on the secretion of milk fat and the composition of blood lipids in the dairy cow were investigated.2. Soya-bean oil increased the yield of total fat, by increasing the secretion of unsaturated C₁₈ acids in milk and also increased the proportions of oleic and linoleic acids in the blood plasma triglycerides.3. Cod-liver oil and Ethive both decreased the yield of total fat and the yields of C₁₄ to C₁₈ acids but had no effect on the yields of C₄ to C₁₂ acids in milk. Although the emulsions contained considerable quantities of C₂₀ to C₂₂ acids, which were incorporated into the blood plasma triglycerides, these acids were not secreted in the milk fat.4. It is concluded that, if the polyunsaturated C₂₀ and C₂₂ acids in cod-liver oil are not hydrogenated in the rumen before their absorption from the digestive tract, they can act directly on the mammary gland, possibly through the inhibition of lipoprotein lipase, to reduce the secretion of long-chain acids in milk. In addition, cod-liver oil may have an indirect effect, through changed volatile fatty acid production in the rumen, on the secretion of short-chain acids in milk.