EFFECTS OF ANDROGENIC AND OESTROGENIC HORMONES ON MATING BEHAVIOUR IN RAMS CASTRATED BEFORE OR AFTER PUBERTY

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Abstract
Adult sheep which had been castrated either before or after puberty were treated with a variety of steroids. The administration of testosterone propionate, oestrone, oestradiol-17β or diethylstilboestrol to animals castrated before puberty caused them to mount oestrous ewes. Oestradiol-17α was less effective than these hormones in this regard, whilst oestriol, hexoestrol and 5α-dihydrotestosterone were ineffective. The response to oestradiol-17β was not altered by the concurrent administration of dexamethasone to block the pituitary–adrenal axis which suggests that oestradiol-17β was not exerting its effect indirectly by causing the release of adrenal steroids. When 5α-dihydrotestosterone was administered in conjunction with oestradiol-17β intromission and ejaculation were observed in addition to mounting behaviour. When rams were castrated as adults their mating behaviour slowly declined over the course of 2 years. After this time, mounting behaviour was rapidly restored by the administration of oestradiol-17β but not by 5a-dihydrotestosterone. These results are consistent with the hypothesis that oestrogens are the ultimate agents responsible for promoting mating behaviour in male animals and hence aromatizable androgens, such as testosterone, are effective whereas non-aromatizable androgens, such as 5α-dihydrotestosterone, are not.