Department of Animal Science, Texas A&M University, College Station, TX, USA.
Adv Exp Med Biol. 2021;1285:43-61. doi: 10.1007/978-3-030-54462-1_4.
Amino acids (AAs) are essential for the survival, growth and development of ruminant conceptuses. Most of the dietary AAs (including L-arginine, L-lysine, L-methionine and L-glutamine) are extensively catabolized by the ruminal microbes of ruminants to synthesize AAs and microbial proteins (the major source of AAs utilized by cells in ruminant species) in the presence of sufficient carbohydrates (mainly cellulose and hemicellulose), nitrogen, and sulfur. Results of recent studies indicate that the ruminal microbes of adult steers and sheep do not degrade extracellular L-citrulline and have a limited ability to metabolize extracellular L-glutamate due to little or no uptake by the cells. Although traditional research in ruminant protein nutrition has focused on AAs (e.g., lysine and methionine for lactating cows) that are not synthesized by eukaryotic cells, there is growing interest in the nutritional and physiological roles of AAs (e.g., L-arginine, L-citrulline, L-glutamine and L-glutamate) in gestating ruminants (e.g., cattle, sheep and goats) and lactating dairy cows. Results of recent studies show that intravenous administration of L-arginine to underfed, overweight or prolific ewes enhances fetal growth, the development of brown fat in fetuses, and the survival of neonatal lambs. Likewise, dietary supplementation with either rumen-protected L-arginine or unprotected L-citrulline to gestating sheep or beef cattle improved embryonic survival. Because dietary L-citrulline and L-glutamate are not degraded by ruminal microbes, addition of these two amino acids may be a new useful, cost-effective method for improving the reproductive efficiency of ruminants.
氨基酸（AAs）是反刍动物胚胎存活、生长和发育所必需的。反刍动物的日粮中的大多数氨基酸（包括 L-精氨酸、L-赖氨酸、L-蛋氨酸和 L-谷氨酰胺）在有足够碳水化合物（主要是纤维素和半纤维素）、氮和硫存在的情况下，被瘤胃微生物广泛代谢，以合成氨基酸和微生物蛋白（反刍动物细胞利用的氨基酸的主要来源）。最近的研究结果表明，成年牛和羊的瘤胃微生物不会降解细胞外的 L-瓜氨酸，并且由于细胞很少或根本不摄取，它们对细胞外 L-谷氨酸的代谢能力有限。尽管反刍动物蛋白质营养的传统研究集中在不能由真核细胞合成的氨基酸（例如泌乳奶牛的赖氨酸和蛋氨酸）上，但人们对在妊娠反刍动物（例如牛、绵羊和山羊）和泌乳奶牛中氨基酸（例如 L-精氨酸、L-瓜氨酸、L-谷氨酰胺和 L-谷氨酸）的营养和生理作用越来越感兴趣。最近的研究结果表明，给营养不足、超重或多产的母羊静脉内注射 L-精氨酸可促进胎儿生长、胎儿棕色脂肪的发育和新生羔羊的存活。同样，给妊娠绵羊或肉牛补充包膜保护的 L-精氨酸或未保护的 L-瓜氨酸可提高胚胎存活率。由于日粮中的 L-瓜氨酸和 L-谷氨酸不会被瘤胃微生物降解，因此添加这两种氨基酸可能是提高反刍动物繁殖效率的一种新的有用且具有成本效益的方法。
