Techniques for improving the fertility rate of donor ewes
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Embryo transfer technology is a powerful method to accelerate the reproduction of high-quality sheep, but improper preparation and careless execution during the process can lead to low utilization rates and difficulties in embryo implantation after ovulation in donor ewes. Based on two years of practical experience from a sheep breeding farm in Shunyi District, Beijing, this article outlines several key measures to improve the conception rate of female sheep following embryo transfer procedures.
**Selection of Donor Ewes**
1. It is recommended to select donor ewes between 1.5 and 4 years of age, with at least one previous lambing, 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 to allow them to recover their health and receive proper nutrition.
3. If using lambs as donors, they must be mature, healthy, free of reproductive diseases, and have had at least two estrus cycles with normal timing.
**Timing 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, ewes show strong estrus activity, making it an ideal time for superovulation. Selecting this period helps ensure smooth surgical procedures, and once the wound heals, timely mating can occur. Artificial insemination is preferred to minimize delays in identifying issues such as endometritis or vaginitis, abnormal estrus, or persistent corpus luteum. Prompt treatment is essential to increase conception rates.
**Surgical Techniques and Frequency**
1. The uterine flushing method is best used 68–72 hours after mating. The donor ewe should not be used more than twice. If she gives birth once and is used again, it confirms that no long-term reproductive issues occurred, ensuring future use and supporting recipient ewes. This approach helps avoid economic losses.
2. Laparoscopic intrauterine flushing is ideal and can be performed up to three times. If the uterus remains uncontaminated, wounds heal quickly, and the estrus cycle remains normal.
**Embracing the Embryo Transfer Process**
1. When washing embryos, the wool around the surgical site must be carefully removed and strictly sterilized to prevent inflammation, which could reduce the ewe's utilization rate.
2. After superovulation, the donor sheep should be bred with fresh semen at intervals of 10–12 hours, up to three times, to avoid excessive contamination of the genital tract, which could affect subsequent breeding success.
3. During the flushing process, care must be taken to avoid bleeding in the fallopian tubes or other areas, as this may cause adhesions or blockages, leading to infertility.
4. The antibacterial solution used during surgery should be changed from penicillin in saline to normal saline combined with lincomycin hydrochloride to prevent uterine ulcers, which can lower utilization and conception rates.
5. After embryo flushing, 800,000 units of penicillin and 1 million units of streptomycin should be diluted in 20 ml of normal saline and injected into the uterus to prevent uterine contamination and improve the reuse rate and conception rate of the donor sheep.
6. After suturing, the peritoneum should be separated from the intestines using the index and middle fingers to avoid suturing the intestines. When suturing the peritoneum, the needle should be pulled out from the inside, and the suture should be tight to prevent later tearing, intestinal sagging, reoperation, or even death of the donor sheep.
**Post-Transfer Care**
1. After embryo flushing, inject 0.8–1 ml of cloprostenol intramuscularly about 10 days after estrus to dissolve multiple corpora lutea, promoting estrus and preventing the formation of persistent corpora luteum.
2. Due to residual exogenous hormones, it’s best to avoid breeding immediately after the first estrus. Some ewes may experience irregular estrus cycles or abnormal ovulation, leading to lower fertility rates. Breeding during the second estrus, especially with LRH-A3 injection, tends to yield better results.
3. If signs of cloudy discharge or uterine inflammation are observed during estrus, flush the uterus and administer anti-inflammatory treatment before breeding to prevent pregnancy complications and missed breeding opportunities.
4. For ewes that have been flushed, the embryos should be placed in the vagina within 13 days after injecting cloprostenol. Estrus can then be used for breeding. In late spring, due to rising temperatures, long-lasting estrus should be managed carefully without artificial stimulation. High temperatures increase the risk of genital tract contamination and lower conception rates. It is better to let them naturally return to estrus and breed in early autumn, significantly improving utilization and conception rates.