Developing bovine milk and mammary gland functions during the first six month of lactation: insights from in‐depth quantitative proteomic analysis (622.6)

Abstract

We applied quantitative bovine milk proteomic data as probes for the developing milk and mammary‐gland function (n = 5 cows with samples of colostrum at day 1 and milk at 1, 2, 3 and 6 months). 1913 protein were identified where 894 were quantified. The majority of proteins express constitutively during mature milk production. Main changes were observed between day 1 and 1 month with 66 and 139 upregulated (FDR‐adjusted p‐value < 0.05) in colostrum and milk, respectively. Proteolytically cleaved intercellular adhesion molecule (ICAM‐1) is upregulated in milk, suggesting that shedding of ICAM‐1 provide a means to suppress leukocyte recruitment into milk as lactation progresses. Shedding of E‐cadherin and catenin (adhesion complex) from mammary epithelium decreases in later milk, which suggests an increasing adherins junction barrier. Housekeeping proteins from blood serum are present at higher abundance in colostrum, which is consistent with the decreased mammary epithelial barrier during colostrum production. Abundance of enzymes in N‐glycoprotein biosynthesis decreases whereas abundance of enzymes in N‐glycoprotein degradation increases from colostrum to milk, indicating decreased N‐glycoprotein biosynthesis over lactation. Lysosomal enzymes are upregulated in milk (fold change > 3), implying higher lysosomal hydrolysis function during later milk production.