Comparative reproduction of the female horse, elephant and rhinoceros: implications for advancing assisted reproductive technologies

Recent loss of rhinoceros subspecies has renewed interest in using more advanced assisted reproductive technologies (ART) in rhinoceroses and elephants. Currently, only semen collection, semen preservation and artificial insemination (AI) have been used repeatedly with success in these species. Although ovum pick-up (OPU) and intra-cytoplasmic sperm injection (ICSI) have been reported recently in rhinoceroses, the techniques are not yet optimised. In contrast, multiple ART applications are routinely used in the horse. Since elephants and rhinoceroses share some reproductive features with equids, we postulate that procedures such as OPU, ICSI, in vitro fertilisation (IVF) and embryo transfer (ET), which are well established in the horse, may represent a basis to develop protocols for endangered pachyderms. In this review, we summarise current knowledge on reproductive physiology relevant to ART. We discuss the current state of ART in all three families and the requirements for the successful implementation of OPU, ICSI, IVF and ET in these species. LAY SUMMARY: Wild rhinoceros and elephant populations are facing ongoing threats; therefore, additional measures are required to protect these species for future generations. Assisted reproductive technologies (ART) include the collection of semen to directly inseminate females or to fertilise oocytes (eggs) in a laboratory to produce embryos, which can be transferred into a recipient female at a later date. While these techniques are routinely used in humans and domestic animals such as the horse, more research is needed to incorporate such technologies into the breeding of elephants and rhinoceroses. As the horse is the closest related domestic species to the rhinoceros, it may serve as the best possible role model. We discuss the current state of ART in the horse, elephant and rhinoceros and the possibilities for future use of these techniques in breeding such endangered animals.