The Effect of Aureomycin on Growth and Protein Utilization in the Rat

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Abstract
Young albino rats were used to study the effect of the addition of aureomycin to diets containing casein, cottonseed meal and soybean meal as sources of protein. Observations were made on growth responses and protein utilization. A growth-stimulating effect of aureomycin was observed when soybean meal and cottonseed meal supplied protein at the 15% level. The effect was less marked with the cottonseed meal at this level than when the protein leyel was raised to 18%. Aureomycin was ineffective when added to casein at the 15% level but brought about increased weight gains with casein at the 9% level. Supplementation of the casein at the 9% level and the soybean and cottonseed-meal proteins at the 15% level with the amino acids considered limiting factors resulted in some increase in growth, but there was further improvement on the addition of aureomycin. This suggests that the aureomycin functioned in a manner beyond that of increasing the availability of the limiting amino acids in the proteins studied. Nitrogen metabolism studies indicated that aureomycin improved the apparent digestibility of the cottonseed- and soybean-meal proteins, but impaired utilization following absorption. This effect was evident to such a degree in rats receiving cottonseed-meal diets that nitrogen retention expressed both in terms of per cent of ingested nitrogen and absorbed nitrogen was actually depressed in antibiotic-supplemented animals.