Effect of heat and solar radiation on vitamin A utilization by the bovine animal

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Abstract
During trial I, twin calves, fed 6 mg carotene daily per 100 lb. body weight, were subjected to high and low ambient temperatures. Differential liver vitamin A analyses indicated that high ambient temperatures predisposed an increased liver vitamin A expenditure. In the first phase of trial II, identical twin calves exposed to solar radiation (SR) for 38 days lost more hepatic vitamin A than their co-twins in the shade (S). Following vitamin A administration, SR stored more hepatic vitamin A than S. Possible mechanisms predisposed by heat stress, that alter vitamin A metabolism, were discussed.