中文摘要：

本试验旨在研究不同蛋白水平日粮对不同形态含氮化合物在血液中^15N丰度及组织中净流量的影响。选择4头体况良好且装有颈动脉、颈静脉、门静脉和肠系膜静脉插管的徐淮白山羊，采用4×4拉丁方设计，配制蛋白水平分别为8．5％、11．0％、13．5％和16．0％的4种日粮。结果表明：血液中pH和蛋白态15N丰度不受蛋白水平影响（P〉0．05）．但显著影响（P〈0．05）总^15N、氨态^15N、尿素态^15N和游离氨基酸态15N丰度，且均在11％蛋白水平下达到峰值：从组织中净流量来看．除蛋白态15N净流量外，PDV和MDV组织中其他各形态舍氮化合物^15N净流量均随日粮中蛋白水平的提高出现先升高后降低的趋势，组间差异显著（P〈0．05），且都在11％蛋白水平下达到峰值。综上可知．日粮蛋白水平为11％时对徐淮白山羊内源尿素氮代谢的周转效果最好。

英文摘要：

This study examined the effects of different protein levels on ^15N enrichment in blood and net flux in PDV and MDV of different forms of nitrogen compounds. Four Xuhuai White goats equipped with carotid artery, mesenteric and portal venous intubations were used in a study designed as a 4×4 Latin square. The protein levels of experimental diets were 8.5%, 11%, 13.5% and 16%. The results showed that different protein levels had no effect on pH and pro- tein-^15Nenrichment in blood （P〉0.05）, but significant effect on total-^15N, NH3-^15N, urea-^15N and free amino acid-15N （P〈0.05）, and the peak values reached at 11% protein level. The net flux of ^15N in PDV and MDV of different forms of nitrogen compounds except protein-15N increased with the increasing protein levels （from 8.5% to 11%） and then decreased （from 13.5% to 16%）. Therefore, based on this study, the results suggested that the optimum CP concentration is 11% and that endogenous urea nitrogen recycling is best for nitrogen metabolism of Xuhuai White goat.