Relationships Between Milk and Milk Fat Composition and Trans-Lactation Changes in Mammary Gland Enzyme Activities in Grazing Cattle

Abstract

Ohanges in milk and milk fat composition during complete lactations of four grazing cows are described. Correlations among the proportions of pairs of milk fat fatty acids were interpreted to indicate that fatty acids were of three groups-those reaching the gland preformed as blood lipids, those synthesized de novo in the gland, and a fraction, chiefly palmitic' acid, derived from both sources. The pro-portions of all groups of acids varied in an erratic manner compared with steady changes observed in other studies with cows on controlled feeding.