The comparative effects of dietary monensin and propylene glycol on insulin resistance of transition dairy cows.

During the transition period, dairy cows suffer from negative energy balance due to the upcoming insulin resistance as a major metabolic disturbance. We hypothesized that providing glucose precursors for transition dairy cows may reduce the insulin resistance. In this study, 24 multiparous Holstein dairy cows were enrolled 8 weeks prior to parturition and divided into 4 equal groups, including control (Ctrl), monensin (Mo), propylene glycol (PPG), and monensin plus propylene glycol (Mo + PPG). Cows from the Mo and PPG groups received 1 mg/kg body weight (BW) of monensin, daily. Cows from the PGG group received 150 g of propylene glycol, daily. Cows from the Mo + PPG group received 1 mg/kg BW of monensin and 150 g/head of propylene glycol daily and Ctrl cows received basal diet without any supplementations. Intravenous glucose tolerance test (ivGTT) was conducted weekly from 3 weeks before to 3 weeks after parturition to evaluate the insulin resistance phenomenon. Immediately after glucose administration, glucose and insulin increased significantly, and their alterations were significant during the study. Glucose and insulin were significantly higher in the Ctrl group than in the other groups, and their levels in different pre- and post-partum periods were significantly lower in the Mo + PPG group than in the other studied groups. The results of this study represented that the supplementary feeding with propionate precursors, such as monensin and propylene glycol, reduced the insulin resistance in dairy cows during the transition period. This effect is more explicit by propylene glycol than by monensin, and the combination of both reduces insulin resistance at higher rates. The use of these dietary supplements is likely to produce more propionates as the main precursor of glucose; therefore, it reduces the negative energy balance and subsequently decreases the insulin resistance. In this regard, to reduce insulin resistance, it is recommended that dairy cows during the transition period be fed with monensin and propylene glycol supplements.