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Relationships of Carotene Intake, Thyro-Active Substances and Soil Fertility to Vitamin A Depletion of Feeder Cattle Fed Corn Silages¹

University of Illinois³, Urbana

Abstract

Feeder steers wintered on corn silages which supplied average daily carotene intakes of 25 to 134 mg. per head were depleted of liver vitamin A stores almost as readily as steers fed a low-carotene diet. Neither nitrate nor other factors directly associated with soil fertilization treatments appeared to be responsible for the apparently poor utilization of silage carotenes. Carotenes isolated from the silages supported liver vitamin A storage in rats, but appeared to be somewhat variable in vitamin A biopotency. Although poor utilization of carotenes was suggested as a major reason for liver vitamin A depletion, apparently the effect was not caused by hypothyroidism in the steers, since treatment with neither triiodothyronine nor Tapazole altered vitamin A status.

¹ The data were taken in part from a thesis submitted by W. M. Durdle to the faculty of the University of Illinois in partial fulfillment of the requirements for the Ph.D. degree.

² Present address: Agricultural and Technical Institute, State University of New York, Cobleskill, N. Y.

³ Department of Animal Science.