Effect of high protein diets and rumen by-pass amino acids on bone growth in sheep

点击翻译按钮获取中文摘要

The study was conducted to elucidate the effect of high protein diets and amino acids reached directly at the upper part of intestine on calcium metabolism, and bone growth and metabolism. Apparent calcium absorption and calcium retention were increased in sheep fed high protein diets. Urinary calcium excretion was also increased by feeding high protein diets. The increase in urinary calcium excretion was thought to be induced by an increase in renal filtration rate of calcium and by little change in calcium reabsorption of renal tubule.Plasma calcium concentration tended to be slightly reduced, and plasma hydroxyproline concentration, which is a marker of bone resorption, was significantly increased in sheep fed the high protein diets. Plasma parathyroid hormone concentration was also elevated by feeding the high protein diets. Therefore, it may be concluded that high protein diets are likely to activate calcium and bone metabolism.In experiments of EDTA infusion, calcium mobilization was larger in sheep fed a high protein diet than in sheep fed a control diet. The results from this experiment support the conclusion that a high protein diet activates bone metabolism.The intra-abomasal infusion of casein tended to increase plasma somatomedin C concentrations and obviously increased plasma insulin concentrations. On the other hand, plasma osteocalcin concentrations which is an indicator of bone formation was not changed by casein infusion. These results indicate that the inflow of high quality protein into the small intestine is likely to enhance bone growth while the response for casein infusion may be affected by the growth stage of animals. The intra-abomasal infusion of alanine and asparaginic acid increased plasma insulin concentrations, while reduced plasma somatomedin C concentrations. It was considerable that hormonal response connected with bone metabolism and growth is changed by a kind and an amount of absorbed amino acid.