7 Oct Chemical ejaculation of the stallion may be necessary if normal means of collection with an artificial vagina is not able to be performed. (Received 5th February ). Summary. The emission of stallion semen was studied with the aid of an `open' Krak\l=o'\wModel artificial vagina. The pattern of mating behaviour was constant in all copulations observed: a mean number of seven intravaginal thrusts was required to elicit ejaculation. The pressure within. thought to be responsible for ejaculation after prostaglandin administration is smooth muscle stimulation. Imipramine alone has been used in research stud- ies for ex copula ejaculation, with success rates ranging 33–37% Imipramine is a tricyclic antide- pressant often used to influence erection, emission, and ejaculation.