Œstrus-inducing Activity of Testosterone in the Ewe

Abstract

ON the basis of results obtained with testosterone administered, together with pregnant mare serum gonadotrophin, to anœstrous ewes Cole¹ suggested that androgen may be responsible for the induction of œstrous behaviour in the sheep. Robinson², however, has shown that œstrogen given following a period of progesterone priming will induce both behavioural and vaginal œstrus in spayed ewes, and it is probable that normal cyclic œstrous behaviour is due to an interaction of these two hormones. In the course of work on the interaction of several steroid hormones on behavioural and vaginal œstrus in spayed ewes, a preliminary trial showed that a single dose of testosterone or of testosterone propionate resulted in mating behaviour in a number of animals. Consequently, a factorial design test, using 72 spayed ewes, was conducted to examine this phenomenon and to define the nature of the apparent œstrous response. The variables introduced (with n = 12) were priming treatment (no progesterone or 10 mgm. per day for 12 days)³, and dose of androgen (1.0, 3.2 or 10.0 mgm.). The androgen was testosterone propionate. Sexual receptivity of the ewes was determined using 8 intact rams fitted with ‘Sire-sine’ harnesses and crayons⁴ and the vaginal response was determined by smears taken for four days following injection of androgen⁵. Results are presented in Table 1.