Growth and protein turnover in animals

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Abstract
Protein turnover is a dynamic process involving most of the tissue proteins: the quantity of protein turned over each day is about 5 to 10 times the daily dietary requirement. Growth, i.e., the accumulation of protein, is the difference between protein synthesized and protein broken down and usually represents only a small fraction of the total protein turned over. Growth rates could be enhanced if protein synthesis, which is energetically expensive, could be increased or if protein degradation, which is energetically much less expensive, could be decreased. Small changes which would be compatible with good health would have significant economic effects on animal and meat production. Millward et al.10 showed that in well‐fed rats, there is a developmental fall in rates of skeletal muscle protein synthesis accompanied by a smaller but parallel decrease in the fractional degradation rate. The result of these changes is a decrease in growth rate with increasingage. Maruyama et al.9 using well‐fed broiler chicks, also observed a developmental fall in the fractional synthesis rate, but a larger decrease in the fractional rate of protein degradation which resulted in a net growth rate much greater than that seen in rats. The results of these and more recent experiments may have a significant impact on meat production.