Effects of Free and Protected Forms of Codliver Oil on Milk Fat Secretion in the Dairy Cow

Abstract

Diets of six lactating cows were supplemented with codliver oil, either free or protected by encapsulation in formaldehyde-treated casein. Protected oil increased yields in milk of 20 to 22 carbon fatty acids but not yield of total milk fat. An inhibition of mammary uptake of plasma fatty acids is proposed to account for this. Free oil similarly increased yields of 20 to 22 carbon fatty acids in milk and additionally reduced the ratio of acetate to propionate in rumen digesta, yields of 4 to 18 carbon fatty acids in milk, and yield of total milk fat. Reduced syntheses of fatty acids in the rumen and mammary gland and reduced mammary uptake of plasma fatty acids are proposed to account for effects of free codliver oil.