Abstract
A basal ration of ground ear corn, soybean meal and minerals was fed to fattening cattle in two experiments designed to determine the optimum level of supplemental vitamin A. In one of the two experiments, levels of 0, 2000, 4000, 8000, 16000 or 32000 international units of vitamin A, per head daily, as vitamin A palmitate, were compared. In the second experiment, levels of 0, 10000, 20000, 30000, 40000 and 50000 I.U. of vitamin A per head daily, were compared in rations which contained no alfalfa, or in rations which contained 10% sun cured alfalfa pellets. The addition of vitamin A to the diet which met the N. R. C. recommendation for carotene levels resulted in increased rate of gain, increased daily feed consumption, decreased levels of plasma carotene, increased levels of plasma vitamin A and increased levels of liver vitamin A. The feeding of 80 mg. of chlortetracycline per head daily for the last 42 days of the experiment decreased the growth rate of cattle fed no supplemental vitamin A, but increased the rate of gain for cattle fed supplemental vitamin A. The feeding of the antibiotic was without apparent effect on feed consumption, levels of carotene or vitamin A in the blood plasma or levels of vitamin A in the liver. Steer calves fed on a ration without alfalfa showed a highly significant increase in daily gain (20%) from an intake of 10,000 I.U. of vitamin A per head, daily. Steers fed 20,000 I.U. of vitamin A per day (Lot 3) gained significantly more than those fed 10,000 I.U. per day. Higher levels—30,000, 40,000 and 50,000 I.U. of vitamin A did not improve the performance of the steers over the 20,000 I.U. intake. All levels of vitamin A fed resulted in an improvement in efficiency of feed conversion of from 7 to 10%. When sun-cured alfalfa pellets made up 10% of the ration, a supplemental level of 10,000 I. U. of vitamin A resulted in a highly significant increase in rate of gain, but higher supplemental levels were without effect. An improvement in feed efficiency of from 4 to 7.5% resulted from vitamin A supplementation of the alfalfa containing ration. Apparently the cattle were able to convert a portion of their vitamin A requirement from the alfalfa. The rations containing no alfalfa contributed from 15.6 to 18.1 mgm. of carotene per animal daily, whereas the rations containing 10% of alfalfa contributed from 42.0 to 46.5 mgm. of carotene, per animal, daily. Stilbestrol caused no significant change in daily gain (control, 1.97 lb.; DES, 2.00 lb.) when the ration was not fortified with synthetic vitamin A. However, improvement in daily gain was highly significant when stilbestrol was used in conjunction with vitamin A supplementation. There was no correlation between the different levels of synthetic vitamin A fed and the response to stilbestrol. Copyright © . .