FOLLICLE GROWTH IN MARES FOR OOCYTE PRODUCTION

R. COCHRAN, M. MEINTJES, D. HYLAND, M. SANSINENA, R.S. DENNISTON, D. PACCAMONTI AND R.A. GODKE

New Orleans, LA, USA

Workshop; From Epididymis to Embryo; 2001

In vitro fertilisation (IVF) of mammalian oocytes has been of interest to scientists for over a century. Successful IVF in humans was first reported in 1978 (Steptoe and Edwards 1978) and use of assisted reproductive technology for treatment of human infertility has increased dramatically since then (Fig 1). Successful IVF in horses was not reported until 1991 (Palmer et al. 1991). Attempts by many others to produce IVF foals have not been successful, making it clear that more research was needed before progress could be made in horses. The reasons for the low success rate of equine IVF remain unclear. Equine oocytes have a thick zona pellucida compared with other species and in vitro maturation of these oocytes takes longer than other domestic farm animal species (Hinrichs et al. 1993). The thick zona pellucida of in vitro matured equine oocytes may act as a barrier to sperm cells prepared in vitro (Li et al. 1995). Zona pellucida hardening, defined as an increased resistance to protease digestion when cultured in serum-free medium, has previously been described in mouse and rat oocytes (De Felici and Siracusa 1982; Zhang et al. 1991), and more recently has been reported to occur in horse oocytes (Fusco et al. 1998). The potentially altered zona pellucida of in vitro-matured oocytes (Chan 1987; Cohen et al. 1990), in addition to less than adequate sperm cell preparation, is likely to contribute to poorer than expected IVF rates in the horse. Thus, interest turned to other approaches to assist fertilisation (eg zona drilling, subzonal sperm injection, intracytoplasmic sperm injection) that had been developed for laboratory animals.