Abstract Methionine is the second or third limiting amino acid in typical swine diets, and exogenous methionine supplementation can improve the efficiency of dietary protein utilization by swine when dietary methionine is limiting. Several feed-grade methionine products, such as DL -methionine and DL -methionine hydroxy analogue free acid, have been on the market for feed formulation. Recently, some feed-grade l -methionine products also became available on the market for swine. However, questions often asked by producers and nutritionists are whether or not more crystalline methionine should be used, and which product should be used. Although a simple answer does not exist, this paper was written to comprehensively summarize our current knowledge in methionine nutrition with an attempt to provide a single source of reference for swine nutritionists and scientists to develop more pertinent answers for different swine production systems. Therefore, in this paper, firstly, different forms of commercially available feed-grade methionine products were reviewed chronologically. Secondly, the overall effectiveness of methionine on swine growth performance was summarized. Thirdly, our current understanding of methionine metabolism in animal body was updated. Fourthly, various biochemical and physiological functions of methionine in swine were described. Lastly, dietary methionine deficiency and toxicity to the animal were pointed out. In brief, it is understood from the cellular metabolism standpoint that methionine functions primarily as a substrate for protein and peptide biosyntheses in the body. From a regulatory standpoint, methionine is an initiator amino acid for universal protein translation. Methionine is also an essential source of methyl groups for methylation of at least seven classes of bioactive compounds, such as DNA, RNA, and proteins. Meanwhile, methionine and some of its derivatives are endogenous antioxidants which can protect living cells from oxidative stress. Synthesized from methionine, a myriad of proteins and peptides are involved in immune system for maintaining animal health. Dietary methionine deficiency negatively affects pig growth performance, while supplementation of more methionine may cause toxic effects. Overall, this paper not only can endorse animal scientists to further explore the underlying metabolic and molecular mechanisms that are responsible for methionine nutrition, particularly in pigs, but also can help the field nutritionists to determine methionine requirements of pigs with different production purposes and to selectively use certain commercial methionine products during their diet formulation practice.

中文翻译：

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猪和相关单胃动物的蛋氨酸营养：超越蛋白质生物合成

摘要 蛋氨酸是典型猪日粮中的第二或第三限制性氨基酸，当日粮蛋氨酸受到限制时，外源性蛋氨酸补充可以提高猪对日粮蛋白质的利用效率。几种饲料级蛋氨酸产品，例如 DL-蛋氨酸和 DL-蛋氨酸羟基类似物游离酸，已投放市场用于饲料配方。最近，一些饲料级 l-蛋氨酸产品也出现在猪市场上。然而，生产商和营养师经常提出的问题是是否应该使用更多的结晶蛋氨酸，以及应该使用哪种产品。虽然不存在简单的答案，本文旨在全面总结我们目前在蛋氨酸营养方面的知识，试图为养猪营养学家和科学家提供单一参考来源，以针对不同的养猪生产系统制定更中肯的答案。因此，本文首先对不同形式的市售饲料级蛋氨酸产品按时间顺序进行了综述。其次，总结了蛋氨酸对猪生长性能的整体效果。第三，更新了我们目前对动物体内蛋氨酸代谢的认识。第四，描述了猪体内蛋氨酸的各种生化和生理功能。最后，指出了饮食中蛋氨酸缺乏和对动物的毒性。简单来说，从细胞代谢的观点可以理解，甲硫氨酸主要用作体内蛋白质和肽生物合成的底物。从监管的角度来看，蛋氨酸是通用蛋白质翻译的起始氨基酸。甲硫氨酸也是甲基化至少七类生物活性化合物（例如 DNA、RNA 和蛋白质）的重要甲基来源。同时，蛋氨酸及其部分衍生物是内源性抗氧化剂，可以保护活细胞免受氧化应激。由蛋氨酸合成的无数蛋白质和肽参与免疫系统以维持动物健康。日粮蛋氨酸缺乏会对猪的生长性能产生负面影响，而补充更多的蛋氨酸可能会产生毒性作用。全面的，