The objective of the present study was to evaluate the effect of length of the FSH superstimulatory treatment on ovarian response and embryo production in sheep. Poll Dorset ewes (n=63) 3.2±0.2 years old weighing 58.5±1.5kg and with a body condition score of 2.7±0.1 (0=emaciated; 5=obese) were used during the transition from the breeding to the non-breeding season. All ewes received an ovarian superstimulatory treatment during the first follicular wave (Day 0 protocol). On Day −9 all ewes received a 0.3-g progesterone intravaginal device (CIDR, Zoetis) for 6 days. On Day −3, the CIDR was removed and all ewes were administered 125μg of cloprostenol sodium intramuscularly (IM) (PGF, estroPLAN, Parnell) and 200IU of equine chorionic gonadotrophin (eCG)+100IU of human chorionic gonadotrophin (hCG) IM (P.G. 600, Merck). Thirty-six hours after CIDR removal (Day −1.5) ewes were administered 100μg of gonadorelin acetate IM (gonadotrophin-releasing hormone, GnRH; Gonabreed, Parnell). Superstimulatory treatments were initiated on Day 0 (84 h after CIDR removal) with a total of 240mg of NIH-FSH-P1 (12 mL, Folltropin, Vetoquinol), and a new CIDR was used from the first to the last FSH dose (6-dose=3 days; 8-dose=4 days). Ewes were randomised to receive the total dose of FSH distributed in eight decreasing doses (8-dose group, n=33) or six decreasing doses (6-dose group, n=30) twice daily 12h apart. Two doses of PGF were administered with the last two doses of FSH, and GnRH was administered 12h after the last FSH administration. Intrauterine AI with fresh semen was performed by laparoscopy 16h after GnRH administration. Ovarian response was determined by laparoscopy 6 days after AI and ova/embryos were collected surgically in ewes with >2 corpora lutea (CL). Data were analysed using generalized linear mixed models (SAS 9.4; SAS Institute Inc.) and presented as mean±s.e.m. in Table 1. The percentage of responding donors (>2 CL) was 93.3% (28/30) and 78.8% (26/33; P=0.5) for the 6-dose and 8-dose groups, respectively. The number of CL tended (P=0.06) to be lesser in ewes in the 6-dose than the 8-dose group. However, no differences (P>0.10) were found in total ova/embryo, fertilized ova, transferable embryos, or freezable embryos. In conclusion, despite a tendency for a greater ovarian response in ewes treated with 8 doses of FSH, embryo yield did not appear to differ after either 6 or 8 doses of FSH administered during the first follicular wave in sheep.
Table 1.
Ovulatory response and embryo production in responding ewes (>2 corpora lutea) superstimulated with either 6 or 8 doses of FSH during the first follicular wave
Outcome
Treatment
P-value
6-dose
8-dose
Number of ewes
28
26
Corpora lutea (n)
14.2±1.7
20.3±2.8
0.06
Total ova/embryos (n)
9.0±1.3
10.9±1.8
0.38
Fertilized ova (n)
8.1±1.4
10.2±1.9
0.34
Fertilized ova (% per ewe)
89.0±5.0
81.7±7.0
0.40
Degenerate embryos
1.3±0.4
2.0±0.8
0.89
Transferable embryos (Grade 1–3)
6.8±1.2
8.2±1.8
0.52
Transferable embryos (% per ewe)
85.7±4.4
75.4±8.4
0.46
Freezable embryos (Grade 1–2)
6.6±1.1
8.2±1.8
0.43
Freezable embryos (% per ewe)
80.5±5.6
75.4±8.4
0.61
Superovulation, fertilization and in vitro embryo development in mice after administration of an inhibin-neutralizing antiserum