A Simple Superovulation Method of A Single Injection of Follicle- Stimulating Hormone Combined with Equine Chorionic Gonadotropin for Superovulation of Suffolk Ewes During the Breeding Season: II. The Ovarian Responses and the Embryo Qualities

Two trials were conducted to investigate the effects of a simple superovulation method using a single injection of porcine follicle-stimulating hormone (pFSH) combined with equine chorionic gonadotropin (eCG) on ovarian responses and embryo qualities in Suffolk ewes during the breeding season. The ewes were treated with a vaginal sponge containing synthetic progestative steroid (P sponge) for 12 days in both trials. In Trial 1 (conducted in 1995), 18 ewes received a single injection (F1) or multiple injections (F6) of a total of 20 mg pFSH, and in combination with an injection of 500 IU eCG (F1+P, F6+P). The injections were conducted on Day -2 (Day 0, was the day of P sponge removal). In trial 2 (conducted in 1996), 24 ewes were given single injections of pFSH and eCG at different times: (i) both hormones on Day -2 (F-2/P-2), (ii) pFSH on Day -2 and eCG on Day -1 (F-2/P-1), and (iii) both hormones on Day -1 (F-1/P-1). One hundred micrograms of an analogue of gonadotropin-releasing hormone (GnRH) was administered on Day 1 in Trial 1 and at the detection of estrus in Trial 2. Frozen-thawed semen was inseminated in utero using a laparoscope at 30 h and 38 h after P sponge removal in Trial 1 and at 18 h after the detection of estrus in Trial 2. Embryos were recovered on Day 7 or Day 8. In Trial 1, the mean number of ovulations and the rate of normal embryos were 6.8, 16.7% for F1, 15.0, 36.0% for F1+P, 15.5, 27.0% for F6 and 20.3, 44.2% for F6+P. The F1+P group showed the results comparable to those of F6 and F6+P. In Trial 2, the mean number of ovulations were 17.8 for F-2/P-1, 13.1 for F-2/P-2 and 12.4 for F-1/P-1. The rate of normal embryos in F-2/P-1 (63.0%) was significantly higher than in F-2/P-2 (41.1%, P<0.05) and tended to be higher than in F-1/P-1 (43.6%, P=0.050). The rate of freezable embryos in F-2/P-1 (56.2%) tended to be higher than in F-2/P-2 (39.3%, P=0.057) and in F-1/P-1 (38.5%, P=0.076). It is concluded that the simple superovulation method of a single injection of 20 mg pFSH combined with 500 IU eCG was as effective as multiple injctions of pFSH, and in combined with eCG on superovulation of Suffolk ewes during the breeding season. Administration of pFSH on Day -2 and eCG on Day -1 was most efficient to induce superovulation in Suffolk ewes.