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Effects of Early Postnatal Dietary Protein Restriction and Repletion on Porcine Muscle Growth and Composition^1,2,

Department of Animal Sciences, Rutgers University, The State University of New Jersey, New Brunswick, New Jersey 08903

Young pigs were fed a low protein diet for varying lengths of time, followed by repletion, to evaluate responses of selected constituents of the longissimus dorsi muscle. Protein restriction was initiated at 2 weeks of age during suckling, and continued to weaning at 5 weeks, to 7 weeks and to 9 weeks (restriction periods 1, 2 and 3 respectively). A group of pigs was repleted for 3 weeks after each restriction period (repletion 1, 2 and 3). Age controls were fed a diet with adequate protein throughout the 12-week study. Body weight, muscle weight and protein, muscle content and concentrations of DNA, RNA and hydroxyproline did not differ from age controls at weaning. The dam, therefore, was able to furnish strong nutritional support even though her diet was inadequate. Restriction periods 2 and 3 resulted in reduced body and muscle weight, and alterations in protein, DNA, RNA and hydroxyproline. Response to repletion was a function of age rather than length of time consuming the low protein diet. Repletion period 1 resulted in a weak general response. Significant changes toward normal in all constituents altered by the low protein diet occurred during repletion periods 2 and 3. Muscle cytochrome oxidase was unaffected by dietary protein level whereas cathepsin D was elevated by the low protein diet. This study suggests an ultimate return to normal muscle composition, but also the unlikelihood that normal size would be obtained by repleted pigs unless there was an extension of the growth period.

KEY WORDS: • dietary protein • porcine muscle • DNA, RNA, hydroxyproline • cytochrome oxidase • cathepsin D

¹ Paper of the Journal Series, Department of Animal Sciences, Rutgers University, The State University of New Jersey, New Brunswick, N. J. 08903.

² Supported in part by Hatch funds.

³ Statistical Consultant, College of Agriculture and Environmental Science, and Assistant Professor, Statistics Center, Rutgers University, The State University of New Jersey.

Manuscript received 10 July 1972.