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Sexual behaviour responses of the ovariectomized ewe to oestradiol benzoate, and their persistent reduction after exposure to phyto-oestrogens

Summary. Characteristics of oestrous behaviour were recorded for 14 control ovariectomized ewes treated with 15, 25 or 40 µg oestradiol benzoate (OB), and for 24 ovariectomized ewes, 11 of which were infertile after prolonged intake of oestrogenic clover, which were each treated successively with 0, 10, 15·6 and 24·3 µg OB.

Squatting by the ewe and Flehmen by a ram after sniffing the ewe were not associated with oestrogen treatment. 'Looking over the shoulder' was a sign exhibited by most ewes treated with 10 µg OB, but not by ewes that did not receive oestrogen. There were no differences between clover-affected and control ewes for these responses.

Active soliciting by the ewe, standing for mounting, and being mounted by the ram, were behavioural responses closely associated with doses of OB greater than 15 µg. Tail fanning and kicking by the ewe were less closely associated with higher doses of OB. All of these responses were slightly but significantly diminished in clover-affected ewes, either in incidence, duration, or by a later time to onset. The results support the hypothesis that prolonged exposure to plant oestrogens causes persistent desensitization of the hypothalamus of the ewe to oestrogen.