Effects of Preovulatory Tranquilization with Xylazine on the Timing of Ovulation in the Horse

Abstract

Xylazine is the most commonly used equine tranquilizer but its effects on ovulation and periovulatory endocrinology have not been tested in the mare. In this study, mares received xylazine (0.5 mg/kg IV) or vehicle during synchronized follicular development. The diameter of the dominant ovarian follicle was monitored every twelve hours by ultrasonography and the time of ovulation was recorded. Serum concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH) and progesterone were measured by radioimmunoassay. Xylazine transiently but significantly increased concentrations of FSH. LH and progesterone profiles as well as follicular diameters and the timing of ovulation were similar following treatment with xylazine or vehicle. A single tranquilizing dose of xylazine is unlikely to alter ovulation in the mare.