Properties of the Colostrum of the Dairy Cow. III. Several Factors Affecting Vitamin A and Carotenoid Content

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Abstract
Factors affecting vit. A and carotenoid contents of colostrum and early milk that were investigated included: individuality of cow, breed, lactation no., type of prepartal ration, and stage in the transition period. The cows received a typical barn ration or the same supplemented with pasture or high levels of vit. A. Analytical samples were obtained by thorough evacuation of the udder by standard milking procedures. Marked individual differences were found in the vit. A content of colostrum from cows of the same breed, lactation, and dietary groups. Carotenoid content of colostrum from Jerseys and Guernseys was higher than that from Holsteins and Ayrshires. Vit. A concn. was higher in colostrum from first-lactation cows than in that from cows in later lactations. Cows on pasture produced colostrum of a higher carotenoid content than did those on barn rations. Early mammary secretions from cows receiving large amts. of vit. A were higher in vit. A than were those from cows on pasture or barn rations. Even when feeding of vit. A was continued postpartally, vit. A in first colostrum was 3 times that in milk 14 days later. The decreases in vit. A and caro-tenoids in colostric fat were rapid during the first 8 milkings, both constituents following a similar logarithmic trend. Breed, no. of lactations, and type of prepartal ration did not seem to influence appreciably the rate of change of vit. A and carotenoids during the early stages.