Abstract
Nulliparous Holstein heifers were administered 20 mg of xylazine for tranquilization before embryo transfer (ET). A frozen-thawed compacted morula embryo from Japanese Black cows was transferred to each heifer, and pregnancy rates were investigated. Division 1 recipients were kept in stanchion stalls, while Division 2 recipients were kept in treatment stalls. The pregnancy rate in the group to which xylazine was administered before transfer (xylazine administration group) tended to be higher than in the control group to which embryos were transferred without xylazine administration in both Divisions 1 and 2 (55.0% vs 48.6% and 50.0% vs 46.2%, respectively). The proportion of Division 1 and 2 recipients requiring 5 or more minutes for ET completion was lower for xylazine treated heifers than for control heifers (10.0% vs 19.0%, respectively). The proportion of Division 1 and 2 recipients leaving blood adhered to the tip of the ET gun was lower for xylazine treated heifers than for control heifers (12.8% vs 22.2%, respectively). These results suggest that administration of xylazine during embryo transfer is effective for improvement in pregnancy rate when nulliparous Holstein heifer recipients are kept in stanchion stalls before transfer.
