Properties of the Colostrum of the Dairy Cow. II. Effect of Prepartal Rations upon the Nitrogenous Constituents

Abstract

20 pregnant heifers and cows were divided into 2 comparable groups, one of which received a ration high in protein and the other a ration low in protein during 7 weeks (avg.) preceding parturition and 8 days following. Differences in concn. of total protein, casein and albumin-globulin fractions in colostrum and early milk from the 2 groups were not significant, but the non-protein N was higher in the mammary products from the group receiving the high-protein ration. During the transition from colostrum to normal milk, decreases in concn. of protein fractions tended to follow a logarithmic curve the first 2 or 3 days, after which the rate of decline was decreased. The reductions in non-protein N continued at approx. the same rate from the 1st day to the 8th. Variations in the N fractions of the mammary secretions became less in succeeding samples.