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Vitamin A Nutrition of Beef Cattle Fed Corn Silages¹

Department of Animal Science, University of Illinois, Urbana

Abstract

Feeder steers were depleted of liver vitamin A stores while wintered on corn silages containing carotenes in quantity considerably in excess of supposed needs. Steers maintained on corn silage feeds through winter and spring developed vitamin A deficiency even though supplemented throughout with 7,000 to 8,000 I.U. daily as preformed vitamin A. Such steers were found to be capable of storing vitamin A administered in massive dose either orally or parenterally. Steers depleted of liver stores while on silage feeds, failed to improve liver vitamin A stores during a subsequent period in which mixed hay and grain provided carotene in excess of supposed needs. Supplementation of this finishing ration with either carotene or preformed vitamin A at levels of 8,000 I.U. or carotene equivalent to 8,000 I.U. of the vitamin daily during the period, March to July, failed to increase liver stores of vitamin A. Some steers exhibited apparent symptoms of early vitamin A deficiency. Increased supplementation at 32,000 I.U. during the final finishing period in the hot weather of July and August failed to improve significantly the liver vitamin A stores unless triiodothyronine treatment was administered.

Intramuscular administration of triiodothyronine (20 mg. per steer per week) increased blood levels of carotene in both supplemented and unsupplemented steers. Triiodothyronine increased liver vitamin A in animals receiving supplemental vitamin A or carotene, and increased blood levels of vitamin A in unsupplemented animals.

¹ The data reported here were taken, in part, from a thesis submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree, University of Illinois. The authors gratefully acknowledge the contributions of W. Huber and R. L. Brewer, College of Veterinary Medicine, University of Illinois, who collected and interpreted data obtained through ophthalmoscopic examinations and conjunctival smears, and J. Simon, Veterinary Pathologist, College of Veterinary Medicine, University of Illinois, who examined the tissue specimens for histological abnormalities.

² Present address: Department of Biochemistry and Nutrition, University of Nebraska, Lincoln, Nebraska.

³ Present address: Fort Lewis A & M College, Durango, Colorado.