Shifts in the Holstein dairy cow milk fat globule membrane proteome that occur during the first week of lactation are affected by parity

Background:The milk fat globule membrane(MFGM)proteomes of colostrum and transition milk are rich sources of proteins that are likely important for neonatal calf health.In addition,characterization of these proteomes could also yield valuable information regarding mammary gland physiology of the early postpartum lactating cow.The objectives of this research were to characterize the MFGM proteomes of colostrum and transition milk through sample collections at four timepoints postpartum,including the first milking(M1,colostrum),second milking(M2,transition milk),fourth milking(M4,transition milk),and fourteenth milking(M14,mature milk),and compare these proteomes between multiparous(MP;n=10)and primiparous(PP;n=10)Holstein dairy cows.Isolated MFGM proteins were labeled using Tandem Mass tagging and analyzed using liquid chromatography-tandem mass spectrometry(LC-MS/MS).Protein identification was completed using MASCOT and Sequest in Proteome Discoverer 2.2.The scaled abundance values were analyzed using PROC MIXED in SAS to determine the effects of milking(MIL),parity(PAR),and MIL×PAR.The adaptive false-discovery rate(FDR)-adjusted P values were determined using PROC MULTTEST.Protein characterization and bioinformatic analysis were completed using a combination of PANTHER,Blast,and Uniprot.Results:A total of 104 common proteins were identified in each of the MFGM samples.Statistical analysis revealed that 70.2%of identified proteins were affected by MIL.Of these,78.1%were lower in M14 compared with M1,including immune-related proteins lactotransferrin,lactadherin and hemopexin.Parity affected 44.2%of proteins.Of the proteins affected by PAR,84.8%were higher in MP cows compared with PP cows,including apolipoprotein E and histones 2A,2B,3,and 4 b.Butyrophilin subfamily 1 member 1A and annexin 5 were higher in samples from PP cows.Milking×parity affected 32.7%of identified proteins,including lactotransferrin,gelsolin,vitamin D binding protein,and S100 proteins.Conclusions:This research supports previous findings that the Holstein MFGM proteome changes rapidly during the first week of lactation.In addition,this research identifies the impact of parity on the colostrum and transition milk MFGM proteomes,which may be important for milk-fed calf health or for the identification of protein biomarkers for mammary functionality.