BackgroundAlthough there are studies on colostrum and milk proteomics of different species in the literature, there is no published report about different quality bovine colostrumsâ proteomics.ObjectivesThe aim of this study was to compare the proteome content of highâ and lowâquality bovine colostrums for the first time.MethodsColostrum samples were collected from 32 Holstein cows from the same farm that had just calved. Brix% levels of colostrums were measured, and then, those with a Brix% value of âĽ27% were classified as highâquality and those with a Brix% value of Ë22% as lowâquality. Three samples from highâquality and lowâquality colostrums were selected and proteomic analyses were performed by pooling separately.ResultsTotally 95 proteins were identified in the colostrums, and 19 of them showed significant changes between highâ and lowâquality colostrums. Expressions in colostrum of glycosylationâdependent cell adhesion moleculeâ1, cofilinâ1, alphaâS2âcasein, alphaâlactalbumin, alphaâ1Bâglycoprotein, actin_cytoplasmicâ1, nucleobindinâ1, cathelicidinâ4, interâalphaâtrypsin inhibitor heavy chain H4, chitinaseâ3âlike protein 1 and monocyte differentiation antigen CD14 were lower, whereas tetranectin, secreted frizzledârelated proteinâ1 (SFRP1), perilipinâ2, coatomer subunit epsilon (COPE), butyrophilin subfamily 1 member A1, polyubiquitinâB, lactadherin and albumin levels were higher in highâquality colostrum than lowâquality colostrum. Moreover, SFRP1, COPE and cathelicidinâ4 proteins were identified for the first time in bovine colostrum. In highâquality colostrum, the most prominently downâregulated proteins were cathelicidinâ4 (26.01âfold) and cofilinâ1 (17.42âfold), and the most prominently upâregulated proteins were COPE (3.37âfold) and tetranectin (3.07âfold).ConclusionsIt was detected that the proteome contents of highâ and lowâquality bovine colostrums were different from each other. As new functions are added to the protein databases regarding these proteins detected in colostrums, the interactions of proteins with each other and with other molecules will be detailed and the effects of highâquality colostrums on passive transfer immunity and calf health will be understood in full detail.