The origin of carotenoids, vitamin A, and tocopherol in colostrum

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Abstract
The changes in quantity of carotenoids, vitamin A, tocopherol, and proteins in the blood plasma of cows near parturition have been further investigated. The cows were pasture-fed but in some cases their carotene and tocopherol intakes had been depressed by drenching with heavy liquid paraffin prior to calving. Close quantitative relationships have been established between decreases in carotene, vitamin A alcohol, and tocopherol in the plasma and the amounts of these substances secreted by the mammary gland at the onset of lactation. It is suggested that, at the start of lactation, these substances are taken up by the mammary gland along with the proteins with which they are associated in the blood plasma and that the increased quantities of these substances in the colostrum result merely from the increased uptake of plasma proteins at that time. The proteins involved appear to be globulins and are associated with the globulin fraction of colostrum.