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 r...