THE BEHAVIOURAL AND VAGINAL RESPONSE OF THE SPAYED EWE TO OESTROGEN INJECTED AT VARIOUS TIMES RELATIVE TO THE INJECTION OF PROGESTERONE

Abstract

SUMMARY: Three trials, each using seventy-two ovariectomized Suffolk cross-bred ewes, were conducted to determine the interaction on the behavioural and vaginal response of varying the time of injection of oestradiol benzoate (ODB; dose levels 16, 20 and 25 μg in oil) relative to that of progesterone (six injections each of 6 mg in oil, spread over 3 days). When ODB was injected before or during the period of progesterone treatment no ewe was served, and the vaginal response was partially suppressed. Maximal behavioural responses were observed when ODB was injected 24–48 hr after the final injection of progesterone. Responses decreased as this interval increased. Maximal vaginal responses were observed when ODB was injected 48 hr or more after the final injection of progesterone. Vaginal sensitivity did not decline with increase in this interval. For assay purposes, using both criteria, it is necessary to inject oestrogen 48 hr after cessation of progesterone treatment in order to obtain a maximal response.