Induction of male behaviour in ovariectomized ewes and ovariectomized-androgenized ewes chronically implanted with oestradiol-17β or testosterone

Normal mature ewes and ewes that had been androgenized with testosterone (T) between days 30–80 or 50–100 of fetal life were ovariectomized and given 100 mg implants of either oestradiol-17β (E) or T. The T implants caused a sustained elevation in plasma T levels but the E implants did not produce stable plasma levels of E. The implants were weighed on removal from the ewes and daily release rates for E and T were 14.4 ± 5.8 μg/kg/day and 24.2 ± 5.3 μg/kg/day respectively.The implants of E induced oestrous behaviour in both the non-androgenized and the androgenized ewes, some of these animals remaining in oestrus for up to 11 days. The ewes also began to mount each other after 1–9 days of treatments; the androgenized ewes also showed male-like aggressive behaviour whereas the non-androgenized ewes did not.The T implants induced oestrous behaviour in both androgenized and non-androgenized ewes. However, the non-androgenized ewes never mounted other ewes, nor did they show aggressive behaviour, whereas the androgenized ewes did.Prenatal androgenization clearly alters the ability of a ewe to respond to exogenous steroids by increasing its propensity to show masculine behaviour. Nevertheless, non-androgenized ewes may also show masculine behaviour during chronic steroid treatment.