127 Influence of breed of recipient on an embryo-transfer program in ewes

The success of embryo-transfer programs depends on factors related to the donor, sire, embryo quality, and recipients used. The selection of the most appropriate genotypes of recipient ewes is essential to obtain high pregnancy rates. The objective of this study was to evaluate the fertility of two breeds of recipient ewes (Dorper and Suffolk) exposed to an embryo-transfer program. The study was conducted from August to September of 2020 at the commercial sheep farm, Rancho Guadalupe, which is located in a temperate area called Huamantla in central Mexico. In total, 76 multiparous healthy ewes in good body condition were used, of which 42 were Dorper and 34 Suffolk. The ewes were synchronised with intravaginal sponges containing 20 mg of micronised cronolone (Chrono Gest, Intervet), which were inserted for 12 days. On Day 10, the ewes were injected intramuscularly with 333 IU equine chorionic gonadotrophin (eCG) (Novormon 5000, Virbac). The oestruses were detected every 6 h with two fertile Dorper rams equipped with an apron, starting 18 h after sponge removal. The time of oestrus was recorded. On Day 6 after oestrus detection, just before embryo transfer, ovulation rate was determined by laparoscopy. The recipients received one embryo of transferable quality (early or expanded blastocyst) within 3 h after its collection, coming from Katahdin donor ewes using a laparoscope and standardised procedures. The embryos were kept in holding medium (Transfer, IVF Bioscience) and were transferred using a capillary glass tube in the ipsilateral horn to the ovary in which ovulation was recorded, and the presence of the best quality corpus luteum was determined based on its size. On Day 35, pregnancy diagnosis was carried out using an ultrasound machine and a 3.5 MHz transabdominal probe (Aloka Prosound 2). The results of the incidence of oestrus and pregnancy rate were analysed as categorical variables with the GENMOD procedure, and ovulation rate with the GLM procedure, both available in SAS. All the ewes were detected in oestrus in both breeds. The incidence of oestrus was similar (P > 0.05) for Dorper and Suffolk ewes at 18 h (78 and 72%) and 24 h (22 and 28%) after sponge removal. Ovulation rate was also similar (P > 0.05) in Dorper and Suffolk ewes (1.52 ± 0.09 vs 1.59 ± 0.10); however, the pregnancy rate was higher (P < 0.05) in Dorper than Suffolk ewes (90.48 vs 70.59%). In conclusion, under the conditions of the study, the results showed the superiority of using Dorper rather than Suffolk multiparous ewes as embryo recipients.