Nutritional Regulation of Protein Synthesis in Ruminants

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Homeotasis of animals is maintained by coordination of protein, carbohydrate and lipid metabolism. For the efficient production of ruminants, therefore, it is important to clarify the relationship between protein synthesis and other nutrient metabolism. In this experiment, the effects of intake and source of energy on metabolism of blood glucose and amino acid, protein synthesis and their relationship were measured. Mature goats were used in this study. They were fed aflalfa hay cubes, ground corn and soybean meal as a basal diet. In this study, three experiments were conducted. They were (1) starch supplementation, (2) non-protein intake and (3) source of carbohydrate. For each experiment, the isotope dilution methods of [U-^<13>C]glucose, [^2H_5]phenylalanine and [^2H_2]tyrosine were conducted and the turnover rates were determined. Protein synthsis rate was estimated from turnover rate of phenylalanine and its oxidation rate to tyrosine. Turnover rates of blood phenylalanine, tyrosine and glucose and protein synthesis increased with increasing energy intake. They were influenced little by source of carbohydrate. Therefore, it was suggested that in goats protein synthesis and nutrient metabolism are influenced by energy intake but not by source of energy.