Sperm Susceptibility to Oxidative Stress in the Retuertas Endangered Horse

In order to determine whether the high level of inbreeding of the Retuertas endangered Horses may increase the vulnerability to oxidative stress of the sperm, the susceptibility to lipid peroxidation (LPO) of sperm membranes was evaluated in cooled extended ejaculates. Extended ejaculates (INRA 96) from four Retuertas horses and nine ejaculates from pure Spanish horses were received within 24 hours of collection at our laboratory. An aliquot was analyzed and served as time 0 control. The rest of the ejaculates were split into two additional aliquots: the first aliquot served as an incubation control and the second aliquot received an oxidative insult (Fe₂SO₄). Membrane LPO, motility parameters, membrane integrity, and mitochondrial membrane potential were evaluated. The oxidative insult induced a significant increase in the percentage of sperm with LPO in the Retuertas horses (P < .05). Total and progressive motility were not affected by the oxidative insult in both groups. However, curvilinear velocity (VCL), average velocity (VAP), straightness index (STR), and amplitude of lateral head displacement (ALH) were significantly affected by the treatment (P < .05) in the Retuertas horse population. The membrane integrity of sperm in this group was also affected: the percentage of sperm with intact membranes decreased (57.31% ± 7.76% vs. 47.52% ± 8.28%); and the percentage of necrotic sperm increased (33.27% ± 7.83% vs. 44.85% ± 9.16%) (P < .05). Finally, the oxidative insult increased the population with low mitochondrial membrane potential in these wild horses. We concluded that the high level of inbreeding of this particular breed apparently leads to a higher susceptibility to lipid peroxidation.