Equine ICSI: an update on semen perspective

Intracytoplasmic Sperm Injection (ICSI) has increased usage in cases of stallion fertility issues, particularly for older stallions, those with reduced sperm numbers or quality, or stallions that have passed away, and only a limited amount of frozen semen is available. By manipulating the frozen semen through thawing, diluting, and refreezing or by cutting the straw under liquid nitrogen, the supply of semen for ICSI can be extended. While ICSI requires a minimal number of spermatozoa per procedure, it is important to consider sperm quality as a crucial factor affecting fertilization and embryo development. Although it is possible to produce healthy embryos and offspring from low quality sperm samples, it is preferable to process and select morphologically and functionally superior sperm to maximize the chances of successful fertilization and embryo development. Several techniques are available for selecting the spermatozoa for ICSI, such as swim-up, washing, density gradient centrifugation, microfluidic sorting, and some combinations. In this review, we will focus on semen type, handling, recent breakthroughs, stallion effects on ICSI efficiency and the prospects of this technology within the equine industry.