Studies on the Carotenoid and Vitamin A Levels in Cattle

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Abstract
Carotenoid and vitamin A values were obtained from liver samples of cows maintained in four dietary groups with different carotenoid and vitamin A intake. The vitamin A levels of the liver were significantly different among three of the four dietary groups, but similar for the shark-liver oil supplemented groups regardless of their basic diet. An optimum level for vitamin A storage was thus indicated. Results obtained from livers of animals which had been maintained on a vitamin A enriched diet 6 to 8 months previously indicated a rather lasting effect on the vitamin A storage of a relatively short period of vitamin A feeding. According to observations made on livers from vitamin A-starved animals and on samples obtained by partial hepatectomy, utilization of stored vitamin A first forces available carotenoid stores to be converted into vitamin A, thus decreasing the carotenoid level without decreasing the vitamin A level. Similarly to the ratios observed in the blood, a typical relationship between carotenoid levels and corresponding vitamin A levels appears to exist in the liver. Changes in the ratio with changing carotenoid levels are probably caused by the tendency of the organism to maintain a constant vitamin A store. The ratio of the liver was found to be modified if the animal was fed vitamin A and in certain pathological conditions. A tendency towards a direct relationship between vitamin A stores and the vitamin A level of the blood was found to exist only when the former fall below normal levels.

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