Effects of Prepartum Monensin Feeding on Energy Metabolism and Reproductive Performance of Postpartum High-Producing Holstein Dairy Cows

This study was designed to determine the effects of monensin in preparturient diet on postpartum milk production, energy metabolism, and reproductive performance of Holstein dairy cows. Forty Holstein dairy cows on close-up period were randomly divided into monensin treated (300 mg/day in close-up ration, top dress) and control groups. Body condition score (BCS) was estimated three weeks before and three weeks after calving. Milk production and milk fat percentage were recorded in both groups within 3 weeks postpartum. Blood samples were collected from five randomly selected cows of each group three weeks after calving. Serum concentrations of insulin like growth factor-I (IGF-I), insulin, glucose, and beta-hydroxybutyrate (BHBA) were measured. Calving to the first observed estrus interval and calving to conception interval were compared between two groups. The results of the experiment showed that loss of BCS (P=0.3), increase of milk production (P=0.9), and milk fat percentage (P>0.05) were not significantly different between two groups during the period of study. In addition, mean serum glucose concentration (P=0.001) and serum insulin concentration (P=0.01) in monensin group were significantly higher than control cows in the first week postpartum. Moreover, serum BHBA concentration did not significantly change in monensin group. Serum IGF-I concentration in monensin group was significantly higher than control group in three weeks postpartum (P