Thermal comfort and seminal traits in stallion reproduction: New methods to understand these relationships.
Authors: Maria Feitosa Ribeiro Luiza, Bersot Gomes João Victor, Hernando Ortiz Vega Wilder, da Silva Alves Andressa, Netto Machado Maurício, Junio Wutke Luan, Raquel Quirino Célia, Carvalho Basile Roberta, Di Filippo Paula Alessandra
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Breeding stallions are typically selected on visual merit with minimal attention to semen quality, yet environmental thermal stress significantly impacts fertility outcomes. Researchers evaluated 24 stallions across summer and winter conditions, combining semen analysis with non-invasive imaging techniques—infrared thermography and Doppler ultrasonography of testicular blood flow—alongside environmental and physiological heat stress measurements. Summer conditions substantially compromised seminal traits, with sperm defects rising from 12.5% in winter to 22.4% in summer, whilst progressive motility and vigour declined from 81.2% and 3.2/5 respectively to 64.2% and 2.7/5; these declines correlated directly with elevated heat stress indices (THI and thermal stress scores). Testicular blood flow velocities demonstrated a clear inverse relationship with heat stress, falling from 33.3 cm/s systolic velocity in winter to 24.4 cm/s in summer, suggesting impaired testicular perfusion compromises spermatogenesis. These findings establish Doppler velocimetry and infrared thermography as practical, non-invasive diagnostic tools for monitoring reproductive health and identifying optimal breeding windows, particularly valuable for practitioners seeking to improve stallion fertility through informed seasonal management and breeding programme timing.
Read the full abstract on PubMed
Practical Takeaways
- •Schedule stallion breeding programs for winter months when testicular blood flow, sperm motility, and semen quality are optimized, avoiding summer heat stress that reduces fertility
- •Use infrared thermography and Doppler ultrasonography as objective, non-invasive screening tools to assess testicular health and predict semen quality, reducing reliance on phenotype alone for breeding selection
- •Monitor environmental temperature and humidity indices (THI) during breeding season; implement cooling strategies or adjust breeding timing when THI exceeds 76-77 to maintain semen quality
Key Findings
- •Sperm defects were significantly higher in summer (22.4%) compared to winter (12.5%), correlating with increased heat stress indices (THI 79.7 vs 73.5)
- •Testicular blood flow velocities (systolic/diastolic), sperm motility, and vigor were all greater in winter (33.3/5.9 cm/s, 81.2% motility) than summer (24.4/4.0 cm/s, 64.2% motility)
- •Significant seasonal correlations were identified between thermal comfort indices and seminal traits in summer, and between Doppler ultrasonography/thermographic data and semen quality in winter
- •Doppler ultrasonography and infrared thermography demonstrated utility as non-invasive tools for assessing testicular circulation, thermal status, and semen quality in stallions