Response of ovariectomized ewes to injection of oestradiol-17 beta at different times of the year.
Long-term ovariectomized Clun Forest ewes were challenged with a range of doses (12.5-50.0 micrograms/injection) of oestradiol benzoate every 2 months from March to November. All treatments induced a biphasic pattern of change in LH concentrations, consisting of an initial depression in concentrations followed by an LH peak, similar to a preovulatory LH surge. The positive feedback response to 12.5 micrograms oestradiol was significantly lower than that after the two higher dose levels, but the magnitude of the response showed no significant seasonal variation. It is concluded that a seasonal change in responsiveness to positive feedback is unlikely to contribute to the absence of ovulation during seasonal anoestrus.
D000818:Animals; D002369:Castration; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000494:pharmacology*; D005246:Feedback; D005260:Female; D007986:Luteinizing Hormone / Q000097:blood*; D012621:Seasons; D012756:Sheep
D004958:Estradiol; D007986:Luteinizing Hormone