EFFECTS OF MONENSIN ON THE METABOLISM OF PERIPARTURIENT DAIRY-COWS

The effects of monensin on plasma concentrations and changes in plasma concentrations of energy metabolites and minerals over time were inve stigated using 24 multiparous Holstein cows. Cows were paired accordin g to farm, predicted date of calving, and body condition score and wer e randomly allocated to two groups. Treated cows were given a ruminal bolus containing 32 g of monensin at 50 +/- 7 d before predicted calvi ng. Treated cows had lower plasma concentrations of glucose, free fatt y acid (FFA), and beta-hydroxybutyrate (BHBA) than did control cows be fore calving, indicating that monensin influenced energy metabolism. H owever, no significant differences in plasma concentrations of glucose , FFA, and BHBA were found between groups after calving. Plasma BHBA c oncentrations increased more before calving in control cows, and plasm a FFA and urea concentrations increased significantly before calving i n all cows. No significant differences in body weight, plasma concentr ations of urea, or whole blood concentrations of glutathione peroxidas e were detected between groups before or after calving. Plasma cerulop lasmin activity did not differ between groups before calving, but was significantly higher in treated cows after calving. Plasma concentrati ons of Ca did not significantly differ between groups before or after calving. Monensin altered both energy and mineral metabolism and has t he potential to improve the health and production of dairy cows.