Branched-chain amino acids in ruminant nutrition: function effects and summary of recent advances

Branched-chain amino acids (BCAAs), including leucine (Leu), isoleucine (Ile), and valine (Val), are a class of amino acids that ruminants are incapable of synthesizing on their own. Available studies confirm that BCAAs and their metabolites play a key role in ruminant physiological processes, such as gastrointestinal digestion and absorption, tissue metabolism, mammary gland development, and immune system functions. However, there is a lack of comprehensive systematic reviews on this topic. Therefore, this paper briefly describes the metabolic characteristics and bioavailability of BCAAs in ruminants, and focuses on the role of BCAAs as functional amino acids, discussing the effects and mechanisms of BCAAs on ruminant physiological functions. Additionally, this paper points out the differences and limitations in the current BCAAs research based on data from all relevant ruminant trials from 2000 to the present. The findings and insights of this review can guide future research to optimize the level and mode of BCAAs supplementation in ruminant feeding programs.