Hair Cortisol, Testosterone, Dehydroepiandrosterone Sulfate and Their Ratios in Stallions as a Retrospective Measure of Hypothalamic-Pituitary-Adrenal and Hypothalamic-Pituitary-Gonadal Axes Activity: Exploring the Influence of Seasonality.
Authors: Olvera-Maneu Sergi, Carbajal Anaïs, Gardela Jaume, Lopez-Bejar Manel
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Seasonal fluctuations in equine stress and reproductive physiology warrant careful consideration when interpreting hair hormone analysis, a non-invasive monitoring tool increasingly used in equine practice. Researchers measured cortisol, testosterone, and dehydroepiandrosterone sulphate (DHEA-S) in hair samples collected bimonthly over twelve months from ten Menorca stallions, using enzyme immunoassay following methanol extraction via the shave-reshave sampling method. Cortisol concentrations peaked during summer months whilst testosterone reached its nadir in spring; DHEA-S showed elevated levels specifically in autumn, with hormone ratios (cortisol/DHEA-S and testosterone/cortisol) varying significantly across seasons. These findings suggest that seasonal photoperiod and environmental changes directly influence both hypothalamic-pituitary-adrenal axis activity (stress response) and hypothalamic-pituitary-gonadal axis function (reproductive status) in stallions, which has important implications for practitioners evaluating chronic stress or reproductive dysfunction. When using hair cortisol concentrations or hormone ratios to assess an individual stallion's welfare or physiological status, clinicians should establish season-specific reference ranges rather than applying single threshold values year-round, as failing to account for these natural cyclical variations risks misdiagnosis and inappropriate management interventions.
Read the full abstract on PubMed
Practical Takeaways
- •Hair cortisol and testosterone testing in stallions must account for season to avoid misinterpretation of stress and reproductive status
- •Summer samples may show elevated cortisol regardless of actual stress levels, while spring samples will underestimate testosterone; baseline seasonal norms should be established
- •Use of hormone ratios (C/DHEA-S and T/C) provides more nuanced assessment of HPA and HPG axis function across seasons than single hormone measurements
Key Findings
- •Cortisol, testosterone, and DHEA-S concentrations in stallion hair are significantly affected by seasonality
- •Cortisol levels peak during summer months while testosterone levels are lowest during spring
- •DHEA-S concentrations are elevated in autumn compared to other seasons
- •C/DHEA-S and T/C hormone ratios vary significantly between seasons, requiring seasonal consideration in interpretation