Piglets obtaining milk from anterior and middle mammary glands (MG) grow faster than those suckling posterior MG, but the underlying mechanisms are not clear. The purpose of this study was to investigate the differential proteomes of colostrum and milk secreted by anterior and posterior MG. Six healthy primiparous sows with 7 pairs of MG were used; the first and the second pairs were defined as anterior MG and the sixth and seventh pairs as posterior MG. Colostrum and milk were collected at d 1 and 14 after parturition, respectively. Comparative proteomics analysis was performed to identify the differentially expressed proteins in colostrum and milk secreted by anterior and posterior MG. Results show that protein composition in colostrum and milk varied markedly with the anatomical location of MG. Immunoglobulins, lactadherin, and haptoglobin were upregulated in colostrum from anterior MG compared with posterior MG. Concentrations of immunoglobulins and lactoferrin in milk from anterior MG were greater than milk from posterior MG. Moreover, concentration of proteins from somatic cells was greater in milk from posterior MG compared with anterior MG. Most proteins, in which abundance was upregulated in colostrum and milk from anterior MG, contribute to passive immunity, intestinal development of suckling piglets and epithelial integrity, and the health of MG. Collectively, these results indicate that in comparison with posterior MG, anterior MG are more active in protein synthesis and produce more immunoglobulins and lactoferrin in colostrum and milk.

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