Ovarian response after a GnRH challenge in seasonally anestrous ewes

To study the ovarian response of seasonally anestrous Corriedale ewes to a gonadotropin releasing hormone challenge, daily transrectal ultrasonography or laparotomy were performed and luteinizing hormone and progesterone profiles were determined. Of the responding ewes (8/17), three ovulated and formed a healthy corpus luteum and five formed large luteinized follicular cysts that secreted low progesterone levels for 2 to 3 d. Therefore, the study of progesterone profiles alone could lead to erroneous interpretations of the ovarian response to GnRH challenge in sheep. Key words: GnRH, progesterone, ovary, anestrous, ultrasonography, ewes