Influence of Antibiotics on the Growth and Protein Metabolism of Young Dairy Calves

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Abstract
Twenty-one two-day-old calves were used to evaluate the effect of Aureomycin and bacitracin on growth and protein metabolism. Calves fed rations containing either antibiotic tended to gain at a faster rate, consumed more calf starter and total feed, and made better utilization of their feed (feed per pound of gain) than did control calves. None of these differences was statistically significant. Neither antibiotic appeared to reduce the incidence of scours. Both antibiotics significantly lowered the coefficients of dry matter and crude fiber digestibility, but neither antibiotic appeared to have any great effect on digestibility of other nutrients or on nitrogen retention. Aureomycin significantly increased blood serum levels of total protein, while bacitracin significantly decreased them; but neither had an appreciable effect on blood levels of urea or non-protein nitrogen. Both antibiotics significantly increased relative serum concentration of albumin and lowered the concentration of alpha-globulin, but had little effect on beta-globulin concentration. Calves fed both antibiotics tended to have lower levels of serum gamma-globulin than did control calves. The results indicate that these antibiotics had little effect on over-all digestion and protein metabolism of the calf, suggesting that the mode of action in stimulating the growth of calves does not appear to be through an effect on protein metabolism or on digestibility.