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

翻譯&校對：上海亙泰實業集團

       瘤胃內的微生物菌群長期以來被認為具有廣泛降解所有日糧氨基酸（AA）的能力。我們的喂養試驗結果表明這個信息是不正確的。本試驗的目的是，在體外實驗中驗證某些AA很少被瘤胃微生物降解的假設。

       來自成年牛只（體重500kg左右，n=6）瘺管的全部瘤胃液體（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 -瓜氨酸分別進行0、0.5、1、2 h的孵育，確定這些AA的代謝隨時間的變化；此外，瘤胃液也用不同劑量（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，以確定這些AA的代謝隨劑量的變化。從設定的孵化時間點進行孵化液的采集（50μL），進行AA分析。

       數據顯示，L–谷氨酰胺被廣泛水解為L -谷氨酸和氨，L -精氨酸被廣泛水解為L -鳥氨酸、L-脯氨酸和氨，但細胞外的L -谷氨酸幾乎沒有分解代謝，細胞外的L-瓜氨酸也沒有被瘤胃微生物降解。細胞對14C標記的L -谷氨酸的吸收很少，對14C標記的L-瓜氨酸的吸收也沒有檢測到。

       這些結果首次表明，成年牛只瘤胃微生物不降解細胞外的L -瓜氨酸，細胞外的L -谷氨酸代謝與它們廣泛分解細胞外的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 μL) 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.（轉自：豬營養國際論壇）