Effect of selenium supplementation on plasma glutathione peroxidase and relationship with inflammatory markers in dairy cows.

The relationship between plasma glutathione peroxidase (GPX-3), inflammatory markers and oxidative status in plasma was investigated on 40 Italian Friesian dairy cows. The cows were subdivided in 5 groups: S3 and S5 contained Se yeast S. cerevisiae CNCM I-3060 (0.31 and 0.50 mg of total Se/kg DM respectively); N3 and N5 contained sodium selenite (0.31 and 0.50 mg of total Se/kg DM respectively); C as negative control (0.09 mg Se/kg DM). Before the start of the study and after 84, 126, and 140 d, blood samples were collected and plasma analyzed for GPX-3, Se, positive (+APP) and negative (-APP) acute phase proteins, reactive oxygen metabolites (ROM), thiobarbituric acid reactive substances (TBARS) and thiol groups (SHp). Data were processed using mixed procedure for repeated measures, and multiple stepwise regression using GPX-3 as dependent variable. Lower value (n.s.) of GPX-3 was observed in C (263 U/l) vs. organic Se (275 and 282 U/L in S3 and S5, respectively) and inorganic Se (305 and 304 U/L in N3 and N5, respectively). The GPX-3 was positively correlated with +APP (haptoglobin: P<0.001; ceruloplasmin: P<0.001), and negatively with albumin (P<0.001). Positive correlations between GPX-3 and ROM (P<0.001), and negative between GPX-3 and SHp (P<0.001) were observed. The GPX-3 variability was mainly explained (51.2%) by haptoglobin content; conversely the contribute of plasma Se was only 3.7%. A negative relationship between +APP/-APP ratio and SHp as well as between -APP/+APP ratio and TBARS was observed; these relationships were significant only in C, N3 and N5 diets. In conclusion our results highlighted that GPX-3 was greatly affected by inflammatory conditions, and also seem to suggest a lower oxidative stress in relation to the inflammatory conditions in Se yeast cows.