Effect of an intraruminal monensin bolus on blood β-hydroxybutyrate, peripartum diseases, milk yield and solids in Holstein cows

Administration of monensin to dairy cows during the transition period may improve cow health, although this is debated. An evaluation of the effects of an intraruminal controlled-released bolus of monensin on health and milk production in transition Holstein cows was done in a Chilean dairy farm. Seventy-seven (77) cows at 21 d before expected parturition were randomly assigned to either a treatment (n= 37) or a control (n= 40) group. The treatment group received a controlled-release oral bolus that delivered sodium monensin at a rate of 335 mg/d for about 95 d. For the first 10 d postpartum cows were clinically examined daily. From 21 d prepartum to 21 d postpartum, data were collected, considering the presence of fever (t°≥ 39.5 °C), postpartum diseases, weekly blood β-hydroxybutyrate (BHB) concentrations, and body condition score. Comparisons of milk production, milk solids (protein and fat percentage) and somatic cell counts (SCC) during the first 100 d of lactation were conducted. Blood BHB concentrations (mmol/L) were similar between groups (P>0.05). No differences were observed on the incidences of ketosis, fever, puerperal metritis, or retained fetal membranes. Endometritis tended to be less frequent in the treatment group than the control group (P=0.08). Monensin did not significantly improve milk yield, fat content, or SCC content. However, cows treated with monensin produced milk with higher protein content during the first week postpartum than the control group (P<0.05). Treated cows also exhibited better improvement on body condition score (P<0.05) between dry-off and parturition and minor losses on body condition score (P<0.05) between parturition and 21 d postpartum than control group