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Effects of High Vitamin A Intake on Milk and Fat Yields and on Vitamin A Constituents in Milk, Blood, and Livers of Dairy Cows¹

Department Of Dairy Husbandry

M. J. Caldwell, D. B. Parrish and J. S. Hughes

Department of Chemistry, Kansas Agricultural Experiment Station, Manhattan

ABSTRACT

The effects of daily supplementary feeding of 1,250,000 USP units of vitamin A in the form of a dry concentrate ("dry vitamin A") to individual lactating cows over a period of 3 months were compared with the results from similar cows on a standard dietary regime. The following conclusions were reached:

1. Vitamin A feeding had no significant effect on total milk and fat production.
   
2. The "dry vitamin A" concentrate did not depress the milk fat percentage.
   
3. The high intake of vitamin A increased the concentration of this vitamin markedly in the milk fat but tended to suppress the carotenoid content.
   
4. Prolonged dietary supplementation of vitamin A increased the level of this vitamin in the blood serum but reduced the carotenoid values. The apparent magnitude of the vitamin A values varied with the analytical procedure used in the assay.
   
5. Supplemental feeding of vitamin A throughout the terminal stages of gestation did not prevent the characteristic declines at parturition but did maintain a higher level at this period than observed in non-supplemented cows.
   
6. The differences in vitamin A intake were reflected in the concentrations of vitamin A in the liver. There was no evidence of a correlation between vitamin A levels in the blood and in the liver of any of the cows that were slaughtered.
   

The authors are grateful to Distillation Products, Inc., Rochester, New York, for supplying the vitamin A supplements ("dry vitamin A"), and to John Morrell and Company, Topeka, Kansas, for their cooperation and assistance in obtaining liver samples.

¹ Contribution no. 165, Department of Dairy Husbandry, and no. 328, Department of Chemistry.