130 Comparative analysis of fertilization success between intracytoplasmic sperm injection and conventional in vitro fertilization in equine reproduction

A recent study by Felix et al. (2022 Biol. Reprod. 107) demonstrated successful outcomes in conventional equine IVF, highlighting its potential as a viable reproductive technology in the equine industry. This development allows for comparison of success rates between the widely used intracytoplasmic sperm injection (ICSI) and conventional IVF. Therefore, this study aimed to compare the fertilization success between ICSI and IVF using equine oocytes. Twelve stock-type mares underwent ovum pickup (OPU) via transvaginal ultrasound-guided follicular aspiration, one mare per replicate; each mare was used once. Immediately following OPU, cumulus–oocyte complexes (COCs) were placed into maturation medium and allocated in a 60:40 ratio to ICSI and IVF treatments, respectively. Fresh semen was donated by a commercial center (no stallion ID provided), with the same ejaculate being used for both fertilization techniques for oocytes aspirated on a given day. For ICSI, only MII oocytes were injected, and cleavage rates were calculated as the proportion of cleaved embryos relative to the total number of injected oocytes (n = 101). The meiotic status of oocytes used in the IVF technique (n = 111) was unknown at the time of fertilization; therefore, the number of MII oocytes was estimated to be 62 based on the maturation rate observed in oocytes denuded for ICSI. Cleavage-stage embryos were identified by cellular division, while blastocysts were recognized by the presence of blastomeres. Differences in cleavage rates, blastocyst development from cleaved embryos, and overall blastocyst development per COC between treatments were evaluated using Fisher’s exact test (GraphPad Software Inc.). Differences were considered significant at P < 0.05 and trends were noted at P < 0.1. A significant difference in cleavage rate was observed between IVF (55/62, 89%) and ICSI (63/101, 63%; P = 0.0003). Additionally, a trend toward significance was noted for blastocyst development from cleaved embryos between IVF and ICSI (P = 0.093). Moreover, overall blastocyst development per initial COC was significantly higher for IVF (26/111, 23%) than for ICSI (20/181, 11%; P = 0.023). These findings suggest that COCs subjected to IVF are more likely to develop into blastocysts compared with those subjected to ICSI. This result highlights the potential of IVF for commercial application in equine reproduction. This study’s limitations include the estimation of MII oocytes in the IVF group and potential variability due to random stallion effects.