Assisted reproduction in equine reproduction: the failure of in vitro fertilisation - the rise of ovum pick-up and associated techniques

Assisted reproduction technologies have become the principle focus if maximising the efficiency and quality of the production of many domestic animals. In equine reproduction, the development of a transvaginal OPU procedure opened the door into in vitro embryo production (IVEP) in this species, which has been heavily limited previously, compared to other animals. This article reviews the literature of many researchers regarding the techniques of OPU, IVF and ICSI; focusing on development of these methods and their adaptation to equine reproduction, and ultimately the emergence of OPU-ICSI in the wake of the failure to establish a successful IVF protocol in the horse. Exploring the shortfalls of IVF elucidates the still limited understanding of many in vivo fertilisation mechanisms in the horse, and the necessity of discovering these unknowns to improve all techniques for IVEP. By looking at the OPU, IVF and ICS] processes in detail, influential factors emerge that affect the success of each procedure, and these can be analysed to further improve ARTs in the future. The continuous evolution of equine ARTs has ensured their position as a keystone of modern sport horse breeding; not only offering the opportunity to preserve valuable genetics, and generate offspring from elite individuals who cannot reproduce through natural means, but also expanding to become a convenient method of breeding normally fertile horse year-round. OPU-ICSI programmes offer a way to circumvent many physiological limitations in the horse, to maximise embryo/offspring production and bypass many fertility issues in both mares and stallions. Since the introduction of each advanced technique, the breeding of sport horses has markedly moved away from traditional breeding management, culminating in the emergence of a niche market for ICS! produced cryopreserved embryos. While in vivo fertilisation rates cannot be equally matched, the efficiency of equine IVEP is constantly improving, and its growing popularity ensures its continued development and advancement in the future.