EFFECT OF TREATMENT WITH IVERMECTIN ON REPRODUCTIVE-PERFORMANCE OF YEARLING BEEF HEIFERS

To determine the effect of treatment with ivermectin on reproductive p arameters, 78 fall-born, yearling heifers were allotted to either an i vermectin treatment group or to the control, non-treatment group. The heifers were treated in June and October when they were approximate ly 7 and 11 mo old, respectively. Ivermectin effectively lowered fecal e gg counts in the treated heifers compared with that of the controls. I n heifers that were maintained on a marginal plane of nutrition, treat ment with ivermectin not only improved weight gains during each record ing period but also hastened the onset of puberty and improved the pre gnancy late during a 60-d breeding season. The positive effect of iver mectin on these reproductive characteristics could not be explained by increased weight gain alone, because the correlation between weight g ain and puberty was not significant. Treatment with ivermectin positiv ely affected pelvic area but not uterine score when compared with thos e of the controls.