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

本研究旨在阐明高蛋白日粮和直接到达肠道上部的氨基酸对钙代谢和骨生长代谢的影响。高蛋白日粮能提高绵羊钙的表观吸收率和存留率。尿钙排泄量也增加喂养高蛋白饮食。尿钙排泄量的增加被认为是由于肾钙过滤率的增加和肾小管钙重吸收的微小变化引起的。血浆钙浓度有轻微降低的趋势，而血浆羟脯氨酸浓度（骨吸收的标志物）在饲喂高蛋白饲料的绵羊中显著增加。血浆甲状旁腺激素浓度也升高喂养高蛋白饲料。因此，可以得出结论，高蛋白质饮食可能激活钙和骨代谢。在EDTA输注实验中，高蛋白质饮食的羊比对照饮食的羊钙动员更大。本实验结果支持高蛋白饲料促进骨代谢的结论，皱胃内注入酪蛋白可使血浆生长调节素C浓度升高，并使血浆胰岛素浓度明显升高。另一方面，酪蛋白输注不改变作为骨形成指标的血浆骨钙素浓度。这些结果表明，高质量的蛋白质流入小肠可能会促进骨生长，而酪蛋白输注的反应可能会受到动物生长阶段的影响。皱胃内输注丙氨酸和天冬氨酸增加血浆胰岛素浓度，同时降低血浆生长调节素C浓度。值得注意的是，与骨代谢和生长有关的激素反应被吸收的氨基酸的种类和数量所改变。

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.