Kyler R Gilbreath，Gayan I Nawaratna，Tryon A Wickersham，M Carey Satterfield，Fuller W Bazer，Guoyao Wu

翻译&校对：上海亘泰实业集团

       瘤胃内的微生物菌群长期以来被认为具有广泛降解所有日粮氨基酸（AA）的能力。我们的喂养试验结果表明这个信息是不正确的。本试验的目的是，在体外实验中验证某些AA很少被瘤胃微生物降解的假设。

       来自成年牛只（体重500kg左右，n=6）瘘管的全部瘤胃液体（3mL，包括微生物）在37℃下，用5mM L-谷氨酰胺、L -谷氨酸、L -精氨酸或L -瓜氨酸分别进行0、0.5、1、2 h的孵育，确定这些AA的代谢随时间的变化；此外，瘤胃液也用不同剂量（0、0.5、2或5 mM）的L -谷氨酰胺、L -谷氨酸、L -精氨酸或L -瓜氨酸孵育2h，以确定这些AA的代谢随剂量的变化。从设定的孵化时间点进行孵化液的采集（50μL），进行AA分析。

       数据显示，L–谷氨酰胺被广泛水解为L -谷氨酸和氨，L -精氨酸被广泛水解为L -鸟氨酸、L-脯氨酸和氨，但细胞外的L -谷氨酸几乎没有分解代谢，细胞外的L-瓜氨酸也没有被瘤胃微生物降解。细胞对14C标记的L -谷氨酸的吸收很少，对14C标记的L-瓜氨酸的吸收也没有检测到。

       这些结果首次表明，成年牛只瘤胃微生物不降解细胞外的L -瓜氨酸，细胞外的L -谷氨酸代谢与它们广泛分解细胞外的L-精氨酸和L -谷氨酰胺的能力相比微不足道。

       Ruminal microbes of adult steers do not degrade extracellular L-citrulline and have a limited ability to metabolize extracellular L-glutamate

       The microbial population within the rumen has long been considered to have the capability of extensively degrading all dietary AA. Results from our feeding trials revealed that this dogma is not correct. In vitro studies were conducted to test the hypothesis that certain AA undergo little degradation by ruminal microbes. Whole ruminal fluid (3 mL, containing microorganisms) from cannulated adult steers (~500 kg, n = 6) was incubated at 37 °C with 5 mM l-glutamine, l-glutamate, l-arginine, or l-citrulline for 0, 0.5, 1, and 2 h to determine time-dependent changes in the metabolism of these AA. Additional ruminal fluid was incubated with 0, 0.5, 2 or 5 mM l-glutamine, l-glutamate, l-arginine, or l-citrulline for 2 h to determine dose-dependent changes in their metabolism. An aliquot (50 ?L) of the incubation solution was collected at the predetermined time points for AA analyses. There was extensive hydrolysis of l-glutamine into l-glutamate and ammonia, and l-arginine into l-ornithine, l-proline, and ammonia, but the near absence of catabolism of extracellular l-glutamate and no degradation of extracellular l-citrulline by ruminal microbes. There was little uptake of 14C-labeled l-glutamate and no detectable uptake of 14C-labeled l-citrulline by the cells. These results indicate, for the first time, that ruminal microbes of adult steers do not degrade extracellular l-citrulline and that metabolism of extracellular l-glutamate is negligible compared with their ability to extensively catabolize extracellular l-arginine and l-glutamine.（转自：猪营养国际论坛）