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Kansas Agricultural Experiment Station, Manhattan
ABSTRACT
A study was made of the effects of individuality, breed, lactation number and prepartal diets on vitamin A and carotenoid contents of colostrum and transitional milk from 86 cows representing four dairy breeds.
Marked individual differences were found in the vitamin A potency of colostrum from cows of the same breed, lactation (first or later) and dietary group. A greater degree of variability was observed in early colostrum than in the milk from the same cows at the end of the transition period. Occasionally, first-lactation cows secreted an atypical colostrum in which vitamin A and carotenoids were abnormally low.
The carotenoid content of colostrum and early milk from Jerseys and Guernseys was higher than in the corresponding secretions from Holsteins and Ayrshires, but differences with respect to Vitamin A were not marked.
Concentrations of vitamin A in the mammary secretions from first-lactation cows generally were higher than in those from cows in later lactations, but consistent differences in carotenoids were not observed.
Access to pasture during the terminal weeks of gestation produced higher levels of carotenoids in colostrum and transitional milk than did typical barn rations. Although levels of vitamin A generally were increased by pasture grazing, the increase was not so great as observed for carotenoids.
High intakes of vitamin A concentrates (500,000 and 1,000,000 I. U. daily, respectively, 4–2 and 2–0 weeks prepartal increased the vitamin A content of colostrum and transitional milk to levels higher than those in corresponding mammary products from cows fed either typical barn rations or pasture.
Supplementation of the ration with 1,250,000 I. U. of vitamin A daily both pre- and postpartally, tended to decrease the concentration of carotenoids in the mammary secretions; but supplementation during the prepartal period only (4–2 and 2–0 weeks, at levels of 500,000 and 1,000,000 I. U. daily, respectively) had no consistent effect on the carotenoids.
Concentrations of vitamin A and carotenoids in first colostrum generally were several times higher than in milk at the end of the transition period. Even when daily supplementation with high levels of vitamin A was continued postpartally, as well as during the prepartal period, the first colostrum averaged almost 3 times higher in vitamin A content than did milk from the same cows 14 days later.
The transition in vitamin A and in carotenoid contents of colostric fat was rapid during the first eight milkings, both constituents following a similar logarithmic trend. Neither number of lactation (first or later), breed, nor prepartal rations seemed to influence appreciably the rate of transition, but in all cases definitely smaller rates of change were evident by the eighth to the tenth milking. Since vitamin A and carotenoids of colostrum are concentrated primarily in the fat, the logarithmic trend usually was manifested more clearly when results were expressed as concentrations per unit of colostric fat instead of as concentrations per unit of total secretion.
1 Contribution no. 372, Department of Chemistry, and no. 178, Department of Dairy Husbandry.
2 Portion of a thesis presented by D. B. Parrish in partial fulfillment of the requirements for the degree Doctor of Philosophy in chemistry at Kansas State College.
3 Present address, Department of Animal Husbandry, Iowa State College, Ames.
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