Achieving in vitro capacitation in stallion sperm remains a key barrier to the large-scale commercialisation of IVF in horses. One proposed explanation is that elevated antioxidant defences in stallion sperm, while protective against oxidative damage, may suppress the ROS-mediated signalling required for capacitation. Unlike human sperm, which rely on glycolysis, stallion sperm use OXPHOS, generating more ROS and requiring robust antioxidant defences. In the context of IVF, stallion sperm must survive a 22-hour incubation at 38.2 °C under capacitating conditions, making it critical to understand how long-term redox balance impacts sperm viability, motility, and functional competence. Motility (CASA), viability (PI), intracellular H₂O₂ (DCF), and DNA integrity (halo assay) were assessed following exposure to increasing H₂O₂ concentrations (0–2000 µM). Catalase activity was selectively inhibited using 3-amino-1,2,4-triazole (3-AT) to evaluate its role in stallion sperm redox regulation (n=18). Stallion sperm showed high resilience to oxidative stress, with IC₅₀ values for progressive motility exceeding 2000 µM, compared to 251.9 µM in humans. Interestingly, despite accumulating more intracellular H2O2 (e.g. at 2000 µM H2O2, stallion sperm DCF fluorescence was 5825±1047 AU vs. 3333±184 AU in human; p≤0.05), stallion sperm exhibited no increase in DNA fragmentation. In contrast, human sperm showed significant DNA damage at 2000 µM H2O2 (12.9±2.2% vs 41.5±7.1%; p=0.0062). Catalase inhibition significantly increased intracellular H₂O₂ in stallion sperm (250 µM: 3.0±1.2% vs 302.4±65.5%; p≤0.0001) and reduced progressive motility (18.9±1.9% vs 5.9±3.7%; p=0.021). While the presence of catalase in mammalian sperm cells is contentious, RT-PCR confirmed catalase expression in stallion sperm, and immunocytochemistry localized it to the post-acrosomal region. Interestingly, sublethal H₂O₂ exposure (250 µM) increased viability (66.5±2.8% vs 71.3±2.9%; p=0.003), consistent with oxidative eustress. These findings highlight redox balance as a critical factor for developing IVF protocols and suggest catalase inhibition as a potential target to enhance equine sperm capacitation outcomes.