Techniques for improving the fertility rate of donor ewes

Embryo transfer technology is a highly effective method for accelerating the reproduction of elite sheep breeds. However, due to insufficient preparation and carelessness during the procedure, it can result in low utilization rates and difficulties in embryo recovery after ovulation in donor ewes. Drawing from the practical experience of a sheep breeding farm in Shunyi District, Beijing, over the past two years, this article briefly outlines some key measures aimed at improving the conception rate of female sheep following surgical procedures. **Selection of Donor Ewes** 1. It is essential to choose donor ewes aged between 1.5 and 4 years, with a history of multiple births, good physical condition, and no reproductive diseases. They should also have a regular estrus cycle during the breeding season. 2. During the feeding period, ewes should be weaned for 30 days, provided with adequate nutrition, and allowed to recover their vitality before the procedure. 3. If using lambs as donors, they must be mature, healthy, free from reproductive diseases, and have experienced at least two estrus cycles with normal timing. **Scheduling of Embryo Transfer** Embryo transfer is typically carried out during the estrus season. In autumn, from late September to late November, and in early spring, from February to April, sheep exhibit strong estrus activity, making these periods ideal for superovulation. Selecting these times facilitates the process and allows for timely mating or artificial insemination after surgery. It is crucial to promptly identify and address any issues such as endometritis or vaginitis, irregular estrus, or persistent corpus luteum. Timely treatment can significantly improve the conception rate. **Surgical Methods and Timing** 1. The uterine flushing method is best performed 68 to 72 hours post-mating. It is recommended that a donor ewe not be used more than twice, and if she successfully gives birth, the second use ensures there are no long-term reproductive complications, thus supporting future transfers and reducing economic losses. 2. Laparoscopic intrauterine flushing is preferred and can be done up to three times. If the uterus remains uncontaminated, wounds heal quickly, and the estrus cycle remains normal. **Emphasis on Embryo Transfer Process** 1. Before the procedure, the wool around the incision site must be removed and strictly disinfected to prevent infection and reduce the risk of complications. 2. After superovulation, the donor should be bred with fresh semen at intervals of 10–12 hours, three times within an hour. This helps avoid contamination of the genital tract and maintains high fertility for subsequent breeding. 3. The flushing process should be gentle and precise to prevent bleeding in the fallopian tubes, which could lead to adhesions or blockages and affect future fertility. 4. Instead of using penicillin in saline, it is better to use normal saline combined with lincomycin hydrochloride to avoid uterine ulcers, which can lower the utilization and conception rates. 5. After embryo retrieval, 800,000 units of penicillin and 1 million units of streptomycin should be diluted in 20 ml of normal saline and administered into the uterus to prevent contamination and increase the chances of reusing the donor ewe. 6. When suturing, the peritoneum should be separated from the intestines carefully to avoid accidental suture of the intestines. The suture should be tightened properly to prevent future complications such as intestinal sagging or reoperation, which can lead to loss of the animal. **Post-Embryo Transfer Care** 1. After embryo flushing, administer 0.8–1 ml of cloprostenol intramuscularly about 10 days after estrus to dissolve multiple corpora lutea and promote regular estrus, avoiding persistent corpus luteum formation. 2. Following embryo retrieval, it is advisable to avoid breeding during the first estrus, as hormonal imbalances may cause irregular ovulation. A second breeding session is often more successful, especially when using LRH-A3 injections to enhance fertility. 3. If signs of cloudy discharge or inflammation are observed during estrus, prompt flushing and anti-inflammatory treatment are necessary to avoid pregnancy complications and missed breeding opportunities. 4. For ewes with long-lasting estrus, especially in late spring, it is better to avoid using aphrodisiacs due to high temperatures, which can increase the risk of genital tract infections and lower conception rates. It is more effective to let them go out of estrus and breed in early autumn, thereby increasing both utilization and conception rates.

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