Techniques for improving the fertility rate of donor ewes

Embryo transfer technology is a highly effective method for accelerating the reproduction of high-quality sheep. However, due to insufficient preparation and careless handling during the procedure, it can result in low utilization rates and difficulties in embryo implantation after ovulation in donor sheep. Drawing from two years of practical experience at a sheep breeding farm in Shunyi District, Beijing, this article outlines several key measures aimed at improving the conception rate of ewes following embryo transfer. **Selection of Donor Ewes** 1. Donor sheep should be between 1.5 to 4 years old, have given birth to at least one lamb, maintain good physical condition, be free from reproductive diseases, and have a regular estrus cycle during the breeding season. 2. During the feeding period, they should be weaned for at least 30 days, provided with adequate nutrition, and allowed to recover their physical strength. 3. If using lambs as donors, they must be mature, healthy, free from reproductive diseases, have had at least two estrus cycles, and show normal estrus patterns. **Scheduling of Embryo Transfer** Embryo transfer is typically conducted 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. Choosing this time frame helps ensure proper recovery after surgery and timely estrus, allowing for artificial insemination. It's important to promptly identify and address issues such as endometritis or vaginitis, abnormal estrus, or persistent corpus luteum, taking immediate corrective actions to improve the overall conception rate. **Surgical Techniques and Timing** 1. The uterine flushing method is best performed 68 to 72 hours post-mating. The donor sheep should not be used more than twice, and if used once, it’s advisable to check for any reproductive disorders before the next use, ensuring the health of both the donor and recipient sheep and avoiding economic losses. 2. Laparoscopic intrauterine flushing is preferable and can be done up to three times. If the uterus remains uncontaminated, wounds heal faster, and the estrus cycle remains normal. **Embracing the Embryo Injection Process** 1. Before the procedure, the wool around the surgical site must be clipped and thoroughly sterilized to prevent infections that could reduce the utilization of the sheep. 2. After superovulation, the donor should be bred with fresh semen at intervals of 10–12 hours, three times within an hour, to avoid over-contamination of the genital tract, which could affect future breeding success. 3. During the flushing process, care must be taken to avoid damaging the fallopian tubes or causing bleeding, which may lead to adhesions or blockages, ultimately reducing fertility. 4. Instead of using penicillin in saline, it's better to use normal saline combined with lincomycin hydrochloride to prevent uterine ulcers, which can lower the utilization and conception rates. 5. After embryo retrieval, mix 800,000 units of penicillin and 1 million units of streptomycin into 20 ml of normal saline and inject it into the uterus to prevent contamination and improve the reuse rate and conception rate of the donor sheep. 6. When suturing the incision, separate the peritoneum from the intestines carefully to avoid accidentally suturing the organs. Ensure the suture is tight and properly placed to prevent future complications like intestinal sagging or reoperation. **Post-Transfer Management** 1. After embryo flushing, administer 0.8–1 ml of cloprostenol intramuscularly about 10 days after estrus to dissolve multiple corpora lutea, promoting estrus and preventing persistent corpus luteum formation. 2. Due to residual hormones in the body, it’s best to avoid breeding immediately after the first estrus. Some ewes may experience irregular cycles or poor ovulation, leading to lower fertility rates even when mated. A second mating, especially with LRH-A3, tends to yield better results. 3. If signs of cloudy discharge or uterine inflammation are observed during estrus, flush the uterus and provide anti-inflammatory treatment before proceeding with breeding to prevent pregnancy complications and missed breeding opportunities. 4. For ewes that have been flushed, embryos should not be left in the vagina for too long. They should be transferred within 13 days, followed by a cloprostenol injection 10 hours later to induce estrus. For late spring ewes, due to rising temperatures, it’s advisable to avoid using aphrodisiacs, as heat can increase the risk of genital tract infections and lower conception rates. Instead, allow them to go out of estrus and breed in early autumn to maximize utilization and conception rates.

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