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Growth in Sheep. Pre - and Post-Weaning Hormone Changes and Muscle and Liver Development^{1 ,2,}

Michigan State University, East Lansing 48824

Abstract

Liver and muscle development, plasma metabolites and serum and endocrine hormone levels were studied during growth of sheep. Tissue RNA, DNA, protein and amino acid contents and serum and endocrine gland hormone levels were studied during the nursing period (birth, 30 and 60 days of age). After weaning, sheep were placed either on an adequate or low protein growing-finishing ration. Tissue and hormone parameters were studied in these sheep at 90 and 120 days of age. During normal growth, pituitary gland, liver, gastrocnemius muscle and adrenal weights increased throughout the 120-day period, but organ weights decreased (P<01) in sheep fed the low protein diet during the growing-finishing period.

During normal growth, total pituitary growth hormone (GH) content increased (P<.01), serum GH levels remained relatively constant but declined by day 120, and serum insulin levels increased (P<.01) with age. Dietary protein restriction lowered serum insulin levels. Plasma essential amino acids (EAA) increased (P<.01) from birth to 30 days of age and then plateaued for the rest of the study, while plasma nonessential amino acids were unchanged throughout the study. Plasma EAA were depressed (P<.01) and N/E ratios were elevated (P<.01) when sheep were fed a low protein ration. Gastrocnemius muscle and liver free amino acid pools behaved similar to the pattern observed in plasma.

Overall, liver, and gastrrocnemius muscle nucleic acid concentrations declined (P<.01) and protein concentrations increased (P<.01) with age. Dietary protein restriction did not markedly effect (except liver RNA) tissue RNA, DNA and protein concentration. Total liver and gastrocnemius muscle nucleic acid and protein content increased (P<.01) with age; however, dietary protein restriction depressed (P<.01) liver DNA and protein and gastrocnemius muscle RNA and protein content. Cell numbers (DNA) of muscle were not affected by dietary treatment.

¹ Michigan Agricultural Experiment Station Journal Article No. 7314.

² The authors express appreciation to Dr. H. A. Henneman and Mr. G. C. Good for the procurement, care and feeding of the sheep.

³ Ruminant Nutrition Laboratory, Department of Animal Husbandry, Michigan State University.

⁴ Present address. Department of Animal Sciences, University of Kentucky, Lexington 40506.