Effect of Rumensin on Health and Reproduction of Lactating Dairy Cows

When Rumensin (monensin sodium) was fed to dairy cows: • Services per conception, days open and calving interval were increased, and firstservice conception rate was reduced in the 22 g/ton group. Pregnancy rates and successful calving rates were similar for all treatment groups. All measures of reproductive efficiency for all doses were well within accepted industry standards. • The incidence of cystic ovarian disease and metritis was increased. • There was no difference in somatic cell counts, or the incidence of clinical or subclinical mastitis. • There was no difference in the involuntary removal rate of cows from the study.