EFFECT OF PREPARTUM ADMINISTRATION OF MONENSIN IN A CONTROLLED-RELEASE CAPSULE ON POSTPARTUM ENERGY INDICATORS IN LACTATING DAIRY-COWS

The effects of monensin on the energy metabolism of dairy cows in earl y lactation were investigated in a large clinical trial that was rando mized and double-blinded. A total of 1010 Holstein cows and first lact ation heifers were allocated to receive a controlled-release capsule o f monensin or a placebo at 3 wk prior to expected calving date. Treatm ents were randomized across 25 dairy farms located near Guelph, Ontari o, Canada. Serum samples obtained at the time of treatment administrat ion and at wk 1, 2, 3, 6, and 9 postcalving were analyzed for beta-hyd roxybutyrate, glucose, aspartate aminotransferase, urea, total protein , calcium, and phosphorus. Cows were also assigned a body condition sc are at the time each sample was obtained. Monensin treatment significa ntly reduced serum beta-hydroxy-butyrate concentrations at wk 1, 2, an d 3 postpartum and significantly raised serum glucose concentrations d uring wk 1 and 2 of lactation. In addition, monensin treatment signifi cantly reduced the loss of body condition score and decreased serum ac tivity of aspartate aminotransferase during the postpartum period. Con centrations of serum urea were significantly higher during wk 2 and 3 postpartum for the cows that were treated with monensin. Monensin trea tment had no effect on the concentrations of calcium, phosphorus, or t otal protein.