| Popis: |
Introduction Improvement of productivity of indigenous sheep is a prerequisite for the in situ preservation of these breeds. Multiple Ovulation and Embryo Transfer (MOET) programs can be used for the quick improvement of sheep populations, but variability in the superovulatory response is limiting their success. So, the establishment of a superovulation protocol suitable for the breed is necessary. We present the results of the first attempt to superovulate Lesvos breed ewes. Materials & Methods Forty five non lactating Lesvos ewes, aged 3-7 years and 4 Lesvos rams were used. All ewes received intravaginal FGA (20 mg) sponges for 12 days. Porcine FSH, at a total dose of 200 mg, divided in either 8 (SOV1, n=18) or 6 (SOV2, n=18) decreasing doses was used to induce superovulation ; additionally, 200 IU eCG were injected at sponge removal. Controls (n=9) were given a single dose of 400 IU eCG at sponge removal. All ewes received 8 μg GnRH 24 hours after sponge removal. The ewes mated under supervision 2-4 times during clinical oestrus. Ova/embryos were collected on day 7 after oestrus onset, soon after slaughter, by uterine horns flushing and evaluated according to morphological criteria. Blood samples were collected throughout the experiment for the determination of progesterone and oestradiol-17β concentrations. In part of the superovulated ewes, ultrasound scanning of the ovaries was performed every 24 hours, beginning before the initiation of FSH treatment and ending 24 hours after GnRH injection. Results & Discussion Eight animals (4 controls, 4 treated) were excluded from the analysis for various reasons. In SOV-2 group more CL, ova and embryos were recorded (18.38±9.42, 13.13±7.71 and 7.88±6.26, respectively) than in SOV-1 group (16.56±7.71, 10.06±7.22 and 5.00±5.73, respectively), though the difference was not significant. No ovarian overstimulation or premature luteal regression was recorded in any of the ewes. The overall fertilization rate was ≈60% ; no difference was found between groups. This relatively low fertilization rate had a negative effect on final embryo yield. Intrauterine A.I. would be expected to significantly improve fertilization rate, but semen collection from Lesvos rams was not possible under the conditions of this experiment. Regression analysis revealed significant relations between steroid hormone concentrations at the beginning of clinical oestrus and the results of superovulation. Moreover, progesterone concentration on the day of slaughter had a significant positive linear relation with the number of CL recorded and ova/embryos collected. Ultrasound scanning of the ovaries did not reveal any difference between groups in the ovarian status at the beginning of treatment. Approximately 77% of the ≥5mm diameter follicles recorded 24 hours after sponge removal had ovulated 24 hours after GnRH injection. In conclusion, successful induction of superovulation in Lesvos ewes is presented for the first time. Porcine FSH (200 mg) resulted in high ovarian response without adverse effects. The 6-doses protocol would be recommended on the basis of better, though not significantly, results obtained (CL, embryos), less labor required and less stress for the animals. Ultrasound scanning of the ovaries 24 hours after sponge removal gives a realistic picture of the final superovulatory response. |
