Effect of treatment with ivermectin on reproductive performance of yearling beef heifers

To determine the effect of treatment with ivermectin on reproductive parameters, 78 fall-born, yearling heifers were allotted to either an ivermectin treatment group or to the control, non-treatment group. The heifers were treated in June and October when they were approximately 7 and 11 mo old, respectively. Ivermectin effectively lowered fecal egg counts in the treated heifers compared with that of the controls. In heifers that were maintained on a marginal plane of nutrition, treatment with ivermectin not only improved weight gains during each recording period but also hastened the onset of puberty and improved the pregnancy rate during a 60-d breeding season. The positive effect of ivermectin on these reproductive characteristics could not be explained by increased weight gain alone, because the correlation between weight gain and puberty was not significant. Treatment with ivermectin positively affected pelvic area but not uterine score when compared with those of the controls.