Abstract: Protein is the basic nutrition for life. As research advanced how to increase the level of MCP in rumen and improve the digestibility of RUP effectively so as to decrease the nitrogen discharge have been the hot topic. While the mechanism of protein, amino acids and peptide were utilized in rumen, small intestine, large intestine and mammary gland were not clear. Now it is possible for us to study metabolism of protein, amino acids and peptide as the molecular biology, blood vessel intubation and arteriovenous disparity technique used. At the same time, active ingredients in milk have earned much attention in recent years. In this article, the authors have reviewed the metabolism of protein in rumen, small intestine, big intestine, mammary gland and factors those affect their use in gastrointestinal, immunoreactive protein in milk and research outlook.

Key words: FONT-FAMILY: 'Times New Roman'; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA">ruminant; amino acids; MCP; RUP; fecaluria; lactoprotein