Production and blood parameters of Holstein cows treated prepartum with sodium monensin or propylene glycol.

Forty-five multiparous Holstein cows were assigned to one of 3 treatments in a randomized complete block design. The objective was to evaluate the effects of sodium monensin (M) and propylene glycol (PPG) during the prepartum period on performance and metabolic parameters during the late dry and first 9 wk postpartum for cows receiving M postpartum. Treatments were: control (C), M in a controlled-release capsule to deliver 335 +/- 33 mg/d for approximately 100 d, and 300 mL/d of PPG drenched orally. Treatments started at 35 and 21 d prior to the expected date of calving for cows receiving M and PPG, respectively. To ensure that all treatments would be restricted to the prepartum period, C and PPG cows received a M controlled-release capsule in the first 24 h after calving. Prepartum propylene glycol administration increased concentrations of glucose and insulin, and decreased beta-hydroxybutyrate and nonesterified fatty acids in plasma prepartum. Milk production was similarly affected by treatments. However, prepartum M treated cows tended to produce more 3.5% fat-corrected milk compared with control, but similar to PPG. Milk fat content and yield tended to be greater for cows that received M prepartum than for C cows, while PPG cows were similar to M and C. Prepartum administration of M decreased milk protein content, but no effect was observed on protein yield.