title: The paradoxical relationship between stallion fertility and oxidative stress.
abstract: The relationship between stallion fertility and oxidative stress remains poorly understood. The purpose of this study was to identify criteria for thoroughbred fertility assessment by performing a logistical regression analysis using "dismount" sperm parameters as predictors and weekly per-cycle conception rate as the dependent variable. Paradoxically, positive relationships between fertility and oxidative stress were revealed, such that samples that produced pregnancies exhibited higher rates of 8-hydroxy-2'-deoxyguanosine release (1490.2% vs. 705.5 pg/ml/24 h) and lower vitality (60.5% vs. 69.6%) and acrosome integrity (40.2% vs. 50.1%) than those that did not. We hypothesized that the most fertile spermatozoa exhibited the highest levels of oxidative phosphorylation (OXPHOS), with oxidative stress simply being a by-product of intense mitochondrial activity. Accordingly, an experiment to investigate the relationship between oxidative stress and motility was conducted and revealed positive correlations between mitochondrial ROS and total motility (R² = 0.90), rapid motility (R² = 0.89), average path velocity (VAP; R² = 0.59), and curvilinear velocity (VCL; R² = 0.66). Similarly, lipid peroxidation was positively correlated with total motility (R² = 0.46), rapid motility (R² = 0.51), average path velocity (R² = 0.62), and VCL (R² = 0.56), supporting the aforementioned hypothesis. The relative importance of OXPHOS in supporting the motility of equine spermatozoa was contrasted with human spermatozoa, which primarily utilize glycolysis. In this study, mitochondrial inhibition significantly reduced the velocity (P < 0.01) and ATP (P < 0.05) content of equine, but not human, spermatozoa, emphasizing the former's relative dependence on OXPHOS. The equine is the first mammal in which such a positive relationship between oxidative stress and functionality has been observed, with implications for the management of stallion fertility in vitro and in vivo.
authors: Priority Research Centre for Reproductive Science, Discipline of Biological Sciences, Faculty of Science and Information Technology, University of Newcastle, Callaghan, New South Wales, Australia zamira.gibb@newcastle.edu.au.
authors: Zamira
authors: Z
authors: Gibb
authors: Priority Research Centre for Reproductive Science, Discipline of Biological Sciences, Faculty of Science and Information Technology, University of Newcastle, Callaghan, New South Wales, Australia.
authors: Sarah R
authors: SR
authors: Lambourne
authors: Priority Research Centre for Reproductive Science, Discipline of Biological Sciences, Faculty of Science and Information Technology, University of Newcastle, Callaghan, New South Wales, Australia.
authors: Robert J
authors: RJ
authors: Aitken
mesh_terms: D000818:Animals; D017849:Animals, Inbred Strains; D015415:Biomarkers / Q000378:metabolism; D005298:Fertility; D006734:Horse Diseases / Q000175:diagnosis / Q000378:metabolism / Q000503:physiopathology*; D006736:Horses / Q000502:physiology*; D007248:Infertility, Male / Q000175:diagnosis / Q000378:metabolism / Q000503:physiopathology / Q000662:veterinary*; D015227:Lipid Peroxidation / Q000187:drug effects; D016015:Logistic Models; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D009517:New South Wales; D010085:Oxidative Phosphorylation / Q000187:drug effects; D018384:Oxidative Stress; D017382:Reactive Oxygen Species / Q000378:metabolism; D055101:Semen Analysis / Q000662:veterinary; D013045:Species Specificity; D013081:Sperm Motility / Q000187:drug effects; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D015415:Biomarkers; D017382:Reactive Oxygen Species; D014475:Uncoupling Agents
keywords: fertility; oxidative phosphorylation; reactive oxygen species; spermatozoa; stallion; thoroughbred