IMIPRAMINE AND XYLAZINE-INDUCED EX COPULA EJACULATION IN STALLIONS

S. M. McDonnell and M. J. Odian
Section of Reproductive Studies - University of Pennsylvania School of Veterinary Medicine
New Bolton Center
Kennett Square, PA 19348-1692

Received for publication: August 18, 1992 Accepted: December 22, 1993

ABSTRACT

This study is a part of our ongoing work toward developing pharmacological methods for enhancing and inducing ejaculation in stallions with ejaculatory dysfunction. We evaluated a combination treatment of imipramine hydrochloride followed 10 minutes later by xylazine hydrochloride for the induction of ex copula ejaculation. Eight pony stallions each underwent 6 treatment trials conducted at 4-day intervals. The trials were conducted in the animalsí stalls, where they were observed for 90 minutes following treatment.  To evaluate the effect of pretreatment sexual stimulation on the rate of ejaculation for each of the 8 stallions, 3 of the 6 trials were preceded by exposure to a restrained ovariectomized pony mare. For 7  of the 8 stallions 1 to 4 of the 6 trials resulted in induced ejaculation, for a total of 16 ejaculations in the 48 trials. Six of the ejaculations occurred with imipramine treatment alone, before the administration of xylazine. All ejaculations were associated with erection and masturbation. Six of 24 trialsí (24 %) preceded by sexual stimulation resulted in ejaculation, while 10 of 24 trials (42%) without sexual prestimulation resulted in ejaculation. These proportions were not different (P =0.11). Induced ejaculates were collected into a plastic bag positioned over the prepuce by a girth strap for the comparison of semen characteristics with 2 base line ejaculates obtained in copula from these stallions during the week preceding the series of induced ejaculation trials (with similar 4-day intervals from previous ejaculation). The induced ejaculates were of lower total volume, higher concentration, lower gel volume, higher total numbers of spermatozoa, and lower pH (P < 0.05) than the base line in copula ejaculates. Together, these semen characteristics suggest increased emission of the sperm-rich fraction and reduced emission o accessory gland fluids, probably resulting from imipramine treatment.