Use of Xylocaine to facilitate embryo transfer to Welsh pony recipient

Abstract

Embryo transfer is a commonly used procedure in equine breeding worldwide. Embryos are trans-cervically transferred into the recipient uterus on Day 5 or 6 after ovulation and expected pregnancy rates range from 65 to 85% and 50 to 75% at days 14 and 45, respectively. Poorer results in pony mares may be attributed to the difficult passage of the cervix and the subsequent contamination of the cervix and/or release of inflammatory products. Paracervical block, i.e. local anesthesia of the cervical area is routinely used for gynecological procedures, such as intrauterine device placement, in women (Mody et al. Obstet Gynecol. 2018; 132(3): 575–582) but has not been reported for similar procedures in the equine. The present study aimed to evaluate the benefits of the application of an anesthetic gel on the cervix before transfer to facilitate the introduction of the transfer gun. Twenty-one grade 1 embryos (one morula and 20 blastocysts), 166-1300µm in diameter (mean±SEM=422±52µm), were collected from Welsh B pony mares at day 7 after ovulation. After collection, embryos were evaluated and conventionally transferred transcervically to recipient pony mares, under 8 years ofage, at day 5, 6, or 7 after ovulation (1 embryo per recipient). In the xylocaine group (XYL), 11 embryos were transferred 10 min after the application of 3ml of xylocaine gel (Xylocaine® gel 2%, AstraZeneca) at the base of the recipient's cervix. Ten other transfers were routinely performed without xylocaine as a control group (CTRL). Pregnancies were monitored by ultrasonography at day 14 and until an embryonic heartbeat was detected at day 21 days. In XYL, 8 (73%) and 6 (55%) recipients were pregnant on day 14 and 21, respectively. In CTRL, 6 (60%) and 4 (40%) recipients were pregnant on day 14 and 21, respectively. While, slightly better in XYL, both at day 14 and day 21, pregnancy rates were not statistically different between groups (P=0.66 and P=0.67 respectively). No significant difference was also obtained between the day of transfer for both groups (P>0.05). Transfers in XYL were subjectively found to be smoother by the operators. It can be concluded that the application of xylocaine on the recipient's cervix does not interfere with early gestation development and may ease cervical catheterization in pony mares. Further work with larger numbers is required to evaluate its potential benefits on transfer outcomes.