Studies on the Carotenoid and Vitamin A Levels in Cattle

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Abstract
The carotenoid and vitamin A levels of the blood of forty-nine cows maintained in four dietary groups with different carotenoid and vitamin A intake, were determined periodically for 1 year. The seasonal changes of the carotenoid level were mainly dependent on the diet, i.e., carotenoid intake, but varied according to the age and breed of the animal. Individual difference, i.e., differences between the means of animals, were found to be statistically significant. Pathological disturbances showed no direct effect on the carotenoid level. The seasonal changes of the vitamin A level were dependent on carotenoid and vitamin A intake and were modified during parturition, abortion and acute infections at which time vitamin A levels showed a sharp, temporary decrease. No statistically significant difference was found between individual animals or age groups, but a difference between breeds was indicated. The vitamin A level rose immediately after administration of shark-liver oil and, according to a preliminary test, after feeding of yeast. The relation of carotenoids to vitamin A in the blood was analyzed. A linear increase of vitamin A with increasing carotenoid levels was found. The ratio of vitamin A to carotenoids at various carotenoid levels was established. This A/car ratio was found to decrease with increasing carotenoid levels, reaching a constant value at high carotenoid levels. Deviations from the normal A/car ratios were found and analyzed. The A/car ratio was below normal in cases of physiological disturbances (parturition, abortion, acute infections), slightly above normal if animals were subject to decreasing carotenoid intake, and well above normal if a vitamin A supplement was fed. The effects of breed differences on the A/car ratio are briefly discussed.