Enhancing Fertility in Mares: Recombinant Equine Gonadotropins

Advanced reproductive technologies have been developed to enhance fertility in mares and stallions. Some of these technologies in mares include superovulation, embryo transfer (ET), intracytoplasmic sperm injection (ICSI), oocyte transfer (OT), gamete intrafallopian transfer (GIFT), and cloning. Superovulation can provide multiple oocytes for these techniques. This review will focus on how recombinant equine follicle-stimulating hormone (reFSH) and recombinant equine luteinizing hormone (reLH) are important for superovulation and ET and may be useful for ICSI, OT, GIFT, and cloning. Superovulation would increase pregnancy rates in normal and subfertile mares and enhance reproductive efficiency when using semen from subfertile stallions. Superovulation depends on a timely interaction of gonadotropins and gonadal feedback in the mare. Historically, several hormone protocols have been used to manipulate follicular waves to increase development and ovulations in cycling, anestrous, and transitional mares. Attempts to superovulate cyclic mares or induce the first ovulation of the year in anestrous or transitional mares using preparations of equine chorionic gonadotropin, gonadotropin-releasing hormone (GnRH), GnRH agonists, porcine FSH, domperidone, sulpiride, equine pituitary extracts, native equine FSH, human chorionic gonadotropin, progesterone, and immunization against inhibin have produced variable results. The use of recombinant technology has improved the ability to produce a reliable product in substantial quantities that is free of other hormones and possible contaminants. Several studies using reFSH and reLH that demonstrate their efficacy to superovulate the mare and induce the first ovulation of the year will be discussed in this review.