Assisted reproduction techniques in the horse

Abstract

This paper reviews current equine assisted reproduction techniques. Embryo transfer is the most common equine ART, but is still limited by the inability to superovulate mares effectively. Immature oocytes may be recovered by transvaginal ultrasound-guided aspiration of immature follicles, or from ovaries postmortem, and can be effectively matured in vitro. Notably, the in vivo-matured oocyte may be easily recovered from the stimulated preovulatory follicle. Standard IVF is still not repeatable in the horse; however, embryos and foals can be produced by surgical transfer of mature oocytes to the oviducts of inseminated recipient mares or via intracytoplasmic sperm injection (ICSI). Currently, ICSI and in vitro embryo culture are routinely performed by only a few laboratories, but reported blastocyst development rates approach those found after bovine IVF (i.e. 25%–35%). Nuclear transfer can be relatively efficient (up to 26% live foal rate per transferred embryo), but few laboratories are working in this area. Equine blastocysts may be biopsied via micromanipulation, with normal pregnancy rates after biopsy, and accurate genetic analysis. Equine expanded blastocysts may be vitrified after collapsing them via micromanipulation, with normal pregnancy rates after warming and transfer. Many of these recently developed techniques are now in clinical use.