Vitamin A Intake in Cattle in Relation to Hepatic Stores and Blood Levels

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Abstract
Hereford steers of about 8 months of age were maintained on a carotene-free basal ration containing vitamin A supplements at levels of 0, 25, 100, 200 and 500 I.U. per pound body weight daily. Serum levels of vitamin A and carotene were determined at 0, 27, 83, 159 and 277 days, and hepatic stores at 0, 166 and 280 days. The animals receiving only the basal ration showed a lower ration consumption and lower average daily gain than those receiving vitamin A supplement. The ration consumption and weight gains were about the same for all lots receiving vitamin A supplement. Dietary vitamin A did not exert a sparing action on hepatic stores of carotene. Blood stores of carotene were depleted sooner than were hepatic stores. Hepatic stores of vitamin A increased in practically a linear relationship with intake throughout the range of vitamin A supplement fed. Serum levels increased rapidly up to an intake of 100 I.U. of vitamin A per pound body weight daily. An intake of 100 I.U. of vitamin A per pound body weight daily will maintain nearly maximum serum levels of vitamin A in cattle under the conditions of the experiment. Serum levels and hepatic stores of vitamin A appear to be controlled by different body mechanisms.