Effects of High Vitamin A Intake on Milk and Fat Yields and on Vitamin A Constituents in Milk, Blood, and Livers of Dairy Cows

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Abstract
Dairy supplementation of the individual rations of 9 dairy cows with 1,250,000 USP units of vitamin A over a period of 3 mos. had no significant effect on total milk and fat production and on milk fat %. The high vitamin A intake increased the conc. of this vitamin in the milk fat and in the blood serum but tended to depress the carotenoid levels. The apparent magnitude of the increase in vitamin A conc. of the blood serum varied with the analytical procedure used in the assay. Termination of the gestation period was accompanied by a decline of the levels of both vitamin A and caro-tenoids in the blood serum. Prepartal dietary supplementation with massive amts. of vitamin A did not prevent the characteristic reduction associated with parturition and initial lactation but did maintain a higher level than noted in non-supplemented cows at this stage. The conc, of vitamin A in the livers from 4 of the cows in the supplemented group was approx. 4 times greater than that in livers from cows on the control ration.