Conventional IVF in the horse past, present, and future: physiological and technical insights.

For decades, conventional in vitro fertilization (IVF) in the horse was ineffective, leading to reliance on intracytoplasmic sperm injection (ICSI) for both research and clinical in vitro embryo production. However, the ability to achieve IVF is essential to the study of key reproductive processes, including sperm capacitation, fertilization, and early embryonic development. Recently we have established a repeatable and efficient IVF system for horses, using long-term (9-22 h) sperm pre-incubation. For clinical use, IVF has many features that may support higher embryo quality than does ICSI, and so may increase the rate of foal production per recovered oocyte. While unlikely to replace ICSI for use with semen of poor quality or limited availability, IVF may eventually provide a clinical alternative to ICSI for normospermic stallions. Work is needed to increase the robustness of the current technique for semen from different sources, to streamline the procedures, and to shorten the time required for capacitation.