1.5), 140 proteins were found to be differentially abundant in sperm from the subfertile stallions when compared to that of the fertile stallions (83 less and 57 more abundant) at 0h incubation. Using bioinformatic analyses, most of the proteins of lower abundance in sperm from subfertile stallions were found to be overrepresented in the "metabolism" (32 proteins) and "metabolism of lipids" (18 proteins) pathways (Homo sapiens orthologs; Reactome database). Two of these proteins, arylsulfatase F (ARSF; log2 fold change = -2.0; p < 0.05) and zona pellucida-binding protein 2 (ZPBP2; log2 fold change = -1.7; p < 0.05), are acrosomal proteins known to play a fundamental role in sperm-oocyte binding. By using immunofluorescence, at 0h of incubation in MW-Lac, ARSF was identified at the acrosome, mid-, and principal piece in sperm from fertile TB stallions, while only at the mid-and principal piece in sperm from subfertile TB stallions. No evidence of ZPBP2 was observed in sperm from both stallion groups at 0h incubation in Lac-MW. Sperm from subfertile Thoroughbred stallions were bound to porcine zonae pellucidae at a lower frequency than sperm from fertile Thoroughbred stallions. In conclusion, DIA-MS is a powerful tool to identify candidate proteins that contribute to the etiology of IAE in Thoroughbred stallions, including proteins of acrosome origin that have a role in the sperm-oocyte binding process.]]>