Utilization of Carotene from Corn Silages by Steers

Abstract

Silages were made from well-eared, well-matured corn which had received a normal rate of fertilization and from corn which had received an additional 200 lb. of nitrogen per acre. Neither silage contained significant amounts of nitrates. However, the high nitrogen-fertilized silage contained less beta carotene. Hereford steer calves grazing green pasture had high initial blood plasma carotenoids but low levels of vitamin A. After being fed a carotene-deficient ration consisting of white corn, molasses dried beet pulp and soybean meal for 61 days, plasma carotenoid levels declined markedly but vitamin A values increased to normal. The carotene-deficient ration at different levels of intake resulted in varying rates of gain but did not influence the rate of vitamin A depletion. Fifty-six steers which had been fed the depletion ration for 137 days were fed silage rations for 126 days. Blood plasma carotenoid and vitamin A levels quickly returned to normal after the silage rations were fed, and supplemental vitamin A had no measureable effect. Forty-two non-depleted steers were fed silage rations for 182 days, followed by a full feed of ground ear corn for 56 days. Feeding 20,000 I.U. of vitamin A per head daily brought about no improvement in performance or carcass value. However, plasma vitamin A values of nonsupplemented steers declined when the ear-corn ration which contained suboptimum amounts of carotene was fed. Growing-fattening steers were able to meet their daily vitamin A requirements from the carotene supplied by the corn silages. There were no apparent differences in feeding value of silages from corn which had received normal or excessive amounts of nitrogen fertilization.