1998 Volume 1998 Issue 35 Pages 12-22
Two trials were conducted to investigate the effects of two different superovulation methods (simple superovulation method using a single injection of porcine follicle-stimulating hormone (pFSH) combined with equine chorionic gonadotropin (eCG) vs. multiple injections of pFSH + eCG) and the breeds of ewes (prolific breed vs. non-prolific breed) on the endocrine profiles of E2 and LH, the ovarian responses and the embryo qualities during non-breeding season.
The ewes were treated with a vaginal sponge containing synthetic progestogen for 12 days in both trials. Twelve Suffolk ewes were used as a non-prolific breed in Trial 1 (conducted in 1995) and 18 Booroola-Dorset cross breed ewes as a prolific breed in Trial 2 (conducted in 1996). They received a single injection of 20 mg pFSH +500 IU eCG (F1+P) or a multiple injections pFSH + 500 IU eCG (F6 + P). The single injection of pFSH and eCG were conducted on Day-2 (Day 0, was the day of sponge removal). The multiple injections of pFSH were conducted during Day 2 to Day 0 in decreasing doses (5, 5, 4, 4, 3, 3, mg). One hundred micrograms of gonadotropin-releasing hormone analogue (GnRH) was administered on Day 1. All ewes in Trial 1 and 3 ewes in Trial 2 were received twice intrauterine artificial inseminations with frozen-thawed semen using a laparoscope. In Trial 2, 8 ewes were received twice intrauterine-cervical inseminations with fresh-diluted semen, and 5 ewes with fresh semen. Embryos were recovered on Day 7 or Day 8. The blood samples were collected from 4 ewes for each group and E2 and LH were determined by EIA.
Differences in the endocrine profiles, superovulatory responses and embryo qualities between the breeds and the treatments were observed. All ovulated ewes in prolific breed were superovulated (>3), while 4 out of 8 non-prolific breed ewes were multiply ovulated (≤3). Good fertilization rates were obtained for non-prolific breed (F1 + P 75.0%, F 6+P 100.0%), but the rates of normal embryos was lower in F 6+P (66.7%) and lowest in F 1 +P (20.0%). In prolific breed, the quality of fertilized eggs and the rates of fertilization with fresh semen (87.7%) were good, though the rates of fertilization with frozen-thawed semen and fresh-diluted semen were low (10.5%, 23.2%). The increase of E2 concentration around estrus for the prolific breed was the same as during the breeding season, while for the non-prolific breed was different with 5 out of 7 ewes showing an early peak of E2 concentration, and then subsequently decreased.
In conclusion, abnormal E2 profile around estrus, low ovarian response and quality of embryos were observed in Suffolk ewes treated by the simple superovulation method, while the better results were obtained with the multiple injection method. The more successive stimulation with gonadotropin may yield better result for superovulation of anestrous Suffolk ewes. On the contrary, normal E2 profiles, good rate of ovulation and quality of fertilized embryos were obtained for anestrous prolific ewes with both simple and multiple superovulation methods. Further investigation is needed to determine an appropriate time for insemination with frozen-thawed semen in anoestrus prolific ewes.
