Preliminary Study On Serum Proteomics In Periparturient Dairy Cows

The objective of this study was to explore the change of serum proteomics in Periparturient Dairy Cows. These results will provide scientific basis for elucidating immune system response at the protein level in dairy cattle during the transition period. This study included three parts:The first part of this study was to study the variation of immune status in the transition period dairy cattle. Thirty-six Chinese Holstein cows were divided into 2 groups which were clinical health cows(n=26)and cows with high somatic cell counts(n=10)according to somatic cell counts in milk after calving. By means of enzyme linked immunosorbent assay (ELISA), the variation of bovine serum immunoglobulin, transferring and albumin in the transition period cows were studied. The serum IgM concentration of the healthy cows had no significantly difference between prepartum and postpartum, cows with high somatic cell count had significantly higher IgM concentration than the clinical healthy cows in peripartum(P=0.03); The serum IgG concentration of the healthy cows decreased in prepartum then increased at postpartum, the serum IgG concentration had no significantly difference between high somatic cell count and clinical healthy cows; The serum IgA concentration of the healthy cows had no significantly difference between prepartum and postpartum, cows with high somatic cell counts had significantly higher IgA concentration than the clinical healthy cows at days 7,21 postpartum(P=0.03; P=0.04); The serum transferrin concentration of the healthy cows increased at prepartum then decreased at parturition, the serum transferrin concentration had no significantly difference between cows with high somatic cell count and clinical healthy cows; The serum albumin concentration of the healthy cows had no significantly difference between prepartum and postpartum, cows with high somatic cell count had higher albumin concentration at prepartum than postpartum. The findings may provide valuable information for the exploring of the relationship of immune function decreased and immunoglobulin, transferrin and albumin during the periparturient cows.The second part of this study was to improve the expression of low-abundance proteins in bovine serum. Low-abundance proteins in bovine serum were enriched by ProteoMiner kit. Serum proteins of the dairy cows were separated and identified using two-dimensional electrophoresis(2-DE) combinated with HPLC tandem ion trap spectrometry. The results showed that, albumin abundance was down-regulation(serum P = 0.01), at the same time, the abundance of other protein such as apolipoprotein E was increased(serum P = 0.01). The findings may provide valuable information for the research of low abundance proteome in serum.The third part this study was to elucidate the molecular mechanisms of immune system suppressed in the periparturient cows. Blood samples were collected at 21 d before expected calving and 1 d after calving from healthy Chinese Holstein heifers (n=8) considered free of mastitis, milk fever and endometriosis based on the somatic cell count and clinical diagnosis. Developmental changes were examined using an integrated proteomic approaches consisting of minor abundance protein enrichment by ProteoMiner, protein label by isobaric tags for relative and absolute quantification (iTRAQ), protein identification by liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS). In total, 78 serum proteins were identified and 19 proteins showed to be differentially expressed at 1 d after calving compared with 21 d before calving. In particular, four proteins including conglutinin, apolipoprotein A-II, deoxyhaemoglobin and ECM1 protein were down-regulated 11.24-, 2.27-, 2.17- and 1.68-fold at 1d postpartum, respectively, while 15 proteins were up-regulated, such as haptoglobin and lipopolysaccharide binding protein. Western blotting validated the relative increases of haptoglobin, which was in agreement with the LC–MS/MS data. These results may provide valuable information to elucidate immune system response at the protein level during the transition period.