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International journal of biometeorology2026; 70(3); 89; doi: 10.1007/s00484-025-03123-y

The fertility of a sub-population of stallions is negatively affected by ambient climatic conditions, mediated through DNA damage.

Abstract: Exposure to systemic heat stress in male mammals adversely affects sperm production, fertility, and DNA integrity. To date, few studies have investigated this phenomenon in horses, particularly in industry-relevant environments. Therefore, this study examined the relationship between ambient climatic conditions and fertility within a population of commercially fertile stallions. Post-coital semen samples ( = 804) were collected weekly from 46 Thoroughbred stallions during two successive breeding seasons (NSW, Australia; 22 weeks total). Semen samples were processed via single-layer colloidal centrifugation on-site to remove contaminants, seminal plasma and poor-quality sperm cells. The remaining sperm fraction was resuspended in Biggers, Whitten and Whittingham (BWW) medium for analyses, including sperm concentration, motility, and DNA damage. Fertility data (first cycle and per-cycle pregnancy rates) were collected from farms. Loggers were placed in the stables and paddocks of stallions to record ambient temperature and humidity, on 3-min cycles. Our results indicate that current management regimens, involving the stabling of stallions at night, with paddock access during the day, expose stallions to highest ambient climatic conditions. Polynomial distributed lag modelling identified 18 stallions whose fertility was adversely affected by heat stress, based on correlations between fertility and ambient climatic conditions ( ≤ 0.05). Of these 18 candidate stallions, six (13% of the overall population) exhibited repeated positive relationships between ambient climatic conditions and sperm DNA damage, and repeated negative relationships between fertility and sperm DNA damage ( ≥ 0.50;  ≤ 0.05). These results suggest that heat-induced subfertility was most likely mediated via oxidative damage to the sperm DNA, and that current management strategies should be assessed to prevent exposure of stallions to maximal climatic conditions. The online version contains supplementary material available at 10.1007/s00484-025-03123-y.
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Publication Date: 2026-03-09 PubMed ID: 41801466PubMed Central: PMC12971856DOI: 10.1007/s00484-025-03123-yGoogle Scholar: Lookup
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  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study investigated how ambient climate, specifically heat stress, negatively impacts the fertility of a subset of Thoroughbred stallions through damage to sperm DNA in commercial breeding environments.

Study Background and Rationale

  • Heat stress in male mammals is known to reduce sperm production, fertility, and DNA integrity, but this has not been widely studied in horses under realistic industry conditions.
  • The researchers aimed to fill this knowledge gap by assessing how natural climatic variations affect stallion fertility on commercial farms over two breeding seasons.

Methodology

  • Subjects: 46 Thoroughbred stallions on farms located in New South Wales (NSW), Australia.
  • Data collection period: Two breeding seasons totaling 22 weeks.
  • Sample collection: 804 post-coital semen samples collected weekly from the stallions.
  • Semen processing: Samples were cleaned using single-layer colloidal centrifugation to remove contaminants, seminal plasma, and poor-quality sperm.
  • Sample analysis: Processed sperm were resuspended in BWW (Biggers, Whitten and Whittingham) medium to assess:
    • Sperm concentration
    • Motility (movement ability)
    • DNA damage
  • Fertility measures: First cycle pregnancy rate and per-cycle pregnancy rate collected from the breeding farms.
  • Environmental monitoring: Temperature and humidity loggers recorded ambient conditions every 3 minutes in both stables and paddocks where stallions were kept.

Key Findings

  • The common management practice was to stable stallions at night and give them paddock access during the day, exposing them to higher daytime temperatures.
  • Statistical modeling using polynomial distributed lag identified 18 stallions whose fertility showed significant negative correlations with heat stress (p ≤ 0.05).
  • Among these 18 susceptible stallions, 6 exhibited:
    • Repeated positive correlations between heat exposure and sperm DNA damage (correlation coefficient ≥ 0.50, p ≤ 0.05).
    • Repeated negative correlations between sperm DNA damage and fertility rates (correlation coefficient ≥ 0.50, p ≤ 0.05).
  • This subset represents approximately 13% of the overall stallion population that was studied.
  • Results indicate that heat-induced subfertility is likely mediated through oxidative damage to sperm DNA rather than other sperm parameters alone.

Implications

  • The study highlights the sensitivity of some stallions to ambient heat exposure and the associated decline in fertility via DNA damage mechanisms.
  • Current management practices may not adequately protect stallions from heat stress, especially since daytime paddock access coincides with peak temperatures.
  • Recommendations include reassessing stallion housing and management regimes to minimize heat exposure during vulnerable periods.
  • Improved environmental control or timing of paddock access could help maintain sperm DNA integrity and fertility rates.

Additional Resources

  • The paper includes supplementary material available online at the provided DOI link for those interested in detailed data and methods.

Cite This Article

APA
Griffin RA, Miller K, Colyvas K, Sheridan A, De Iuliis G, Aitken RJ, Baker MA, Gibb Z, Swegen A. (2026). The fertility of a sub-population of stallions is negatively affected by ambient climatic conditions, mediated through DNA damage. Int J Biometeorol, 70(3), 89. https://doi.org/10.1007/s00484-025-03123-y

Publication

International journal of biometeorology
ISSN: 1432-1254
NlmUniqueID: 0374716
Country: United States
Language: English
Volume: 70
Issue: 3
PII: 89

Researcher Affiliations

Griffin, Róisín A
  • Infertility and Reproduction Research Program, Hunter Medical Research Institute, New Lambton Heights, Australia. roisin.griffin@newcastle.edu.au.
  • School of Environment and Life Sciences, College of Engineering, Science and Environment, University of Newcastle, Callaghan, Australia. roisin.griffin@newcastle.edu.au.
Miller, Kasey
  • School of Environment and Life Sciences, College of Engineering, Science and Environment, University of Newcastle, Callaghan, Australia.
Colyvas, Kim
  • School of Engineering (Statistics), College of Engineering, Science and Environment, University of Newcastle, Callaghan, Australia.
Sheridan, Alecia
  • School of Environment and Life Sciences, College of Engineering, Science and Environment, University of Newcastle, Callaghan, Australia.
De Iuliis, Geoffry
  • Infertility and Reproduction Research Program, Hunter Medical Research Institute, New Lambton Heights, Australia.
  • School of Environment and Life Sciences, College of Engineering, Science and Environment, University of Newcastle, Callaghan, Australia.
Aitken, Robert John
  • Infertility and Reproduction Research Program, Hunter Medical Research Institute, New Lambton Heights, Australia.
  • School of Environment and Life Sciences, College of Engineering, Science and Environment, University of Newcastle, Callaghan, Australia.
Baker, Mark A
  • Infertility and Reproduction Research Program, Hunter Medical Research Institute, New Lambton Heights, Australia.
  • School of Biomedical Sciences and Pharmacy, College of Health, Medicine and Wellbeing, University of Newcastle, Callaghan, Australia.
Gibb, Zamira
  • Infertility and Reproduction Research Program, Hunter Medical Research Institute, New Lambton Heights, Australia.
  • School of Environment and Life Sciences, College of Engineering, Science and Environment, University of Newcastle, Callaghan, Australia.
Swegen, Aleona
  • Infertility and Reproduction Research Program, Hunter Medical Research Institute, New Lambton Heights, Australia.
  • School of Environment and Life Sciences, College of Engineering, Science and Environment, University of Newcastle, Callaghan, Australia.

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