Spermatozoal acrosome dysfunction and its role in stallion subfertility

Cases of stallion subfertility due to acrosome dysfunction have been recognized since the 1990s. While some of these were observed in stallions with reduced sperm motility and morphology, a more severe form has been reported in stallions with normal-to-excellent sperm quality parameters, which is also uniquely observed in individuals of the Thoroughbred registry. These stallions carry a susceptibility genotype (A/A-A A in the gene FKBP6, exon 5) for Impaired Acrosomal Exocytosis (IAE). Current clinical observations from our group have identified a few highly subfertile stallions from other breed registries that also display a lower ability to undergo acrosomal exocytosis (AE) but do not carry the A/A-A/A genotype. This document provides a concise review of the role of acrosome dysfunction as a cause of stallion subfertility, including methods to estimate acrosome function and clinical descriptions of IAE in TB and non-TB stallions.