In horses, the progress of the study of the early events of fertilization has been slow compared with that in other large domestic animals.
The development of assisted reproduction technologies (ART) in the horse dates back to the late nineteenth century with the establishment of the first equine pregnancies obtained by artificial insemination (Heape, 1898). However, progress in assisted reproduction in the horse has been rapid in the last decade. ART covers a range of procedures (IVP, oocyte pick-up (OPU), oocyte transfer (OT), ICSI and cloning), all of which have the ultimate aim of assisting the ‘infertile’ mare to become pregnant and deliver a live offspring (Galli et al., 2007).
The development of techniques such as ultrasound-guided aspiration of follicles (Brück et al.,1992; Bracher et al., 1993; Cook et al., 1993; Dippert et al., 1994), which allowed the utilization of live mares as donors of in vivo matured oocytes, and immature oocytes destined to in vitro maturation, has lead to some clinical interest. However, standard IVF, is not efficient in the horse. Although OT can be used as an efficient method for production of foals from isolated oocytes, attempts to fertilize equine oocytes in vitro have resulted in only limited progress. Successful IVP depends on a number of factors: availability of healthy immature oocytes, efficient and repeatable methods for IVM, physiological sperm capacitation, and subsequent optimum embryo in vitro culture systems. The success rates of some individual steps involved in equine IVP mare still far from allowing their use in routine protocols as in cattle.
Recent progress and difficulties in assisted reproduction in the horse is the focus of this review, with the emphasis on the procedures of OPU, OT, ICSI and cloning.