Abstract: Mammary gland is the main site to synthesize milk. To improve the conversion efficiency of dietary nutrients (energy and protein) into milk and increase the yield of milk and protein content, it is necessary to clarify amino acid metabolism in the mammary gland. In this article, the authors have reviewed the supply of amino acid, uptake of amino acid by mammary gland, metabolism of amino acid by udder, and effect of energy on milk protein synthesis, thus providing a basis for further study and maniputation of output of milk.

Key words: Lactating, Mammary gland, Amino acid metabolism, Ruminant