Intracytoplasmic sperm injection zone: insights and applications from a university-based assisted reproduction laboratory

Abstract

Intracytoplasmic sperm injection (ICSI) has become one of the most important tools used for in vitro production of embryos (IVP) in equine reproduction management programs around the world. This procedure is often performed in the US for several breeds and is used primarily to optimize foal production for broodmares and performance mares but also for stallions with limited semen availability or poor semen quality. As such, there are a limited number of US laboratories capable of using this method, which requires advanced training of personnel and specialized equipment. Many veterinarians and breeding farms currently aspirate ovarian follicles in cycling mares and ship oocytes to ICSI-capable laboratories, where embryos can be produced and typically vitrified for ultralow temperature storage and transport for transfer to recipient mares and establishment of surrogate pregnancies. The Veterinary Assisted Reproduction Laboratory in the School of Veterinary Medicine at the University of California, Davis, maintains a 3-dimensional approach to equine assisted reproductive technology. We offer commercial solutions to breeders, educational advice and training to other laboratories, veterinarians, and visiting scholars. Moreover, as a research laboratory, our objective is to analyze and apply observations from IVP to elucidation of complex developmental problems such as embryonic and fetal loss. In 2018, we reported the birth of the first foal produced at UC Davis using ICSI, and we have since developed a commercial ICSI program for practitioners and horse breeders in the US. Today, our laboratory receives thousands of immature oocytes for ICSI sessions every year, with an average of 2 embryos per mare-session. Our research is focused on molecular, cellular and genetic aspects of gamete biology, perifertilization events, and early equine development using an array of tools including advanced microscopy, sequencing, and time-lapse imaging of developing embryos. In this review, we have highlighted our laboratory’s current methods for commercial equine IVP and research and clinical studies conducted to optimize IVP in horses.