IVF with frozen-thawed sperm after prolonged capacitation yields comparable results to ICSI in horses: A morphokinetics study

Intracytoplasmic sperm injection (ICSI) is the current clinical practice for the in vitro production of equine embryos. The use of conventional fertilization methods such as in vitro fertilization (IVF), has historically been associated with poor success in horses. However, recent improvements have led to better outcomes with IVF, though only when using fresh semen, which limits its use in clinical practice. IVF remains in its infancy in equine reproduction, and several unknowns remain about the technique. One significant gap in knowledge concerns the morphokinetics of IVF embryos and how they differ from their ICSI counterparts. To address this, we performed IVF using frozen-thawed sperm from five different stallions following sperm selection and a prolonged capacitation period of 10 h, on a total of 109 oocytes. We then analyzed the cleavage rate (cleaved/initial oocytes), blastocyst rate (blastocyst/initial zygotes), and blastocyst development (blastocyst/cleaved zygotes) of the IVF cycles, and compared them with those of the clinical ICSI cycles during the same period. We also evaluated time-lapse images of the developed embryos to assess developmental time points such as time to morula compaction and blastocyst expansion, as well as morula and blastocyst sizes. Overall, developmental rates were not different between IVF and ICSI cycles (blastocyst rate 41.1 % IVF and 41.8 % ICSI, p > 0.05). However, development proceeded faster in IVF cycles (blastocyst expansion IVF 155.5 ± 18.5 h; ICSI 167.2 ± 19.6 h; p