Ovarian responses of seasonally anestrous ewes administered progesterone,PMS, HCG and(or) GnRH

One hundred and sixty ewes were assigned to sixteen groups in a 2 × 2 × 4 factoral design and were treated during the anestrous season. The main effects were progesterone pretreatment (non-implanted and implanted for 14 days), PMS pretreatment (no pretreatment and pretreatment with 500 IU at the time of progesterone implant removal) and treatments (none, GnRH in saline, GnRH in gelatin capsules and HCG). GnRH in saline (250 μg) and HCG (500 IU) were administered intramuscularly and GnRH in gelatin capsules (250 μg) was administered subcutaneously 24 hours after the time of progesterone implant removal.Ewes were classified into one of four progesterone response categories: cyclic, transient, prolonged and no response. An injection of GnRH in saline induced a prolonged progesterone response in only one ewe (13%) which was similar to the response in the untreated ewes (0%). More ewes administered GnRH in gelatin capsules (56%) and more ewes administered HCG (89%) had a prolonged progesterone response than GnRH (in saline) treated or untreated ewes. A higher percentage of ewes that were pretreated with PMS and treated with GnRH in saline (78%) had a prolonged progesterone response than ewes treated with either PMS (22%) alone or with GnRH (in saline; 13%) alone.