Label-free quantitative proteomics analysis reveals the fate of colostrum proteins in the intestine of neonatal calves

The contribution of intestinally absorbed colostral immunoglobulins to the transmission of passive immunity is widely reported in neonatal calves. However, changes in the colostral proteome in the gastrointestinal digesta remain unclear. Therefore, this study aimed to investigate changes in colostral proteome affected by gastrointestinal proteases in neonatal calves. Twenty-one neonatal Holstein calves were used in this study, including 18 colostrum-fed calves slaughtered at 8 (CI, n = 6), 24 (CII, n = 6), and 36 h (CIII, n = 6) postpartum and 3 milk-fed calves slaughtered 24 h postpartum (MI, n = 3). The ingested colostrum and milk samples were collected from the mid-jejunum segment, following the sacrifice. The undigested colostrum or milk along with their ingested colostrum or milk samples were investigated using a label-free proteomics approach. Hierarchical clustering and principal component analysis of the quantified proteins revealed that the ingested colostrum from the CII and CIII groups and the ingested mature milk from the MI group appeared to share similar patterns. Analysis of the intestinal digesta revealed a time-dependent decrease in caseins, lactoferrin, and osteopontin protein levels, and an increase in cationic trypsin, chymotrypsin, and carboxypeptidase. Several protease inhibitors, such as α-1-antiproteinase, α-2-antiplasmin, and early lactation protein, were identified in the colostrum and intestinal digesta. In addition, we detected identical levels in the intestinal digesta and colostrum for albumin, α-1-acid glycoprotein, and plasminogen. Pathway analysis indicated that proteins increased in the intestinal digesta belonged to the following categories: biosynthesis of antibiotics, carbon metabolism, and biosynthesis of amino acids. These results indicated that selected colostral proteins were digested by gastrointestinal proteases, contributing to their intestinal absorption in calves. These findings provide new insights into the fate of the colostral proteome in the gastrointestinal tract and may aid in the identification of factors contributing to health management in neonatal calves.