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Animals : an open access journal from MDPI2023; 13(13); doi: 10.3390/ani13132129

Hair Cortisol and Testosterone Concentrations in Relation to Maturity and Breeding Status of Male Feral Horses.

Abstract: Steroid-hormone concentrations from non-invasively obtained biomarkers, like hair, can provide a representation of circulating hormones diffused over relatively long time periods (e.g., weeks or months). The hormone cortisol is often associated with physiological or even psychological stress, while testosterone is strongly associated with male development and reproductive success. Increasingly, studies are using hormone levels derived from hair to make inferences among both domestic animals and wildlife. For horses, all previous hair hormone analysis has been done on companion or working animals. We evaluated the levels of hair cortisol (n = 153) and testosterone (n = 48) from 136 feral horses living on Sable Island, Canada that have been part of a long-term individual-based study since 2008. This population has been undisturbed and unmanaged for over 50 years, and exhibits the natural social organization for horses, harem defense polygyny. Hair samples were collected in mid to late summer and the segment analyzed corresponds with hair grown during, and following, the peak of the reproductive season. Social position was determined based on the male's role as either a dominant breeding Stallion (Stallion), a non-breeding subordinate male (tag), adult Bachelor (5 years old or older), or Immature male (2-4 years of age). While there was no difference in hair-cortisol concentration among any class of adult males (i.e., Stallion, tag, or Bachelor), Immature males had significantly lower hair cortisol concentrations than the other groups (p = 0.001). Hair testosterone levels among the four social positions were significantly higher among Stallions (p = 0.04). Hair testosterone concentration was also significantly related to the probability of a male being either a Bachelor or Stallion and was the only variable remaining in AICc model selection (p = 0.016, AICc = 32.3, Null AICc = 38.8). While not a significant relationship, Stallions had a negative correlation between hair cortisol concentrations and testosterone (R2 = -0.20, p = 0.383), and Bachelors, conversely, had a positive association (R2 = 0.43, p = 0.246). Our observations of hormone concentrations in relation to physiological, social, or reproductive parameters in this population suggest trends that are similar to what has been established using blood or other matrices.
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Publication Date: 2023-06-27 PubMed ID: 37443926PubMed Central: PMC10339860DOI: 10.3390/ani13132129Google Scholar: Lookup
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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.

The research study investigates the relationship between hair cortisol and testosterone concentrations among male feral horses in relation to their maturity and breeding status. The uniqueness of this research comes from using hair as a non-invasive method of obtaining biomarkers for long-term hormone level assessment.

Objectives and Methodology

  • The research aimed to analyze the concentrations of cortisol and testosterone in the hair of feral horses on Sable Island, Canada and establish relationships with their maturity and breeding status. This population has been unmanaged and undisturbed for over 50 years, providing a setting for a natural social organization of horses to be studied.
  • 136 feral horses’ hair samples were examined for cortisol (153 samples) and testosterone levels (48 samples). The samples were collected in mid to late summer, which corresponds with hair growth during and after the peak of the reproductive season.

Findings

  • Horses were categorized based on their role within the herd as adult breeding stallions, non-breeding subordinate males, adult bachelors, and immature males between two to four years of age.
  • There was no variation in hair cortisol concentration among adult males, whether stallions, non-breeding subordinates, or bachelors. However, immature males appeared to have significantly lower hair cortisol levels than the other groups.
  • Stallions showed significantly higher hair testosterone levels compared to the other statuses.
  • There appeared to be a significant relationship between high testosterone concentration and the likelihood of a male horse being a bachelor or stallion, remaining as the only variable in the model selection of statistical analysis.

Interesting Discoveries

  • Negatively associated testosterone and cortisol concentrations were observed in Stallions, though insignificant.
  • Conversely, Bachelors displayed a positive correlation between testosterone and cortisol concentrations, despite the statistical insignificance.

Conclusion

The research study successfully provided insightful findings on the hormone levels of feral horses in relation to their social and breeding statuses, contributing significantly to the understanding of horses’ physiological and reproductive behaviour in the wild. The trends observed in this study proved to parallel those previously observed using other matrices like blood, indicating the effectiveness of hair as a non-invasive means of monitoring long-term hormone levels.

Cite This Article

APA
Medill SA, Janz DM, McLoughlin PD. (2023). Hair Cortisol and Testosterone Concentrations in Relation to Maturity and Breeding Status of Male Feral Horses. Animals (Basel), 13(13). https://doi.org/10.3390/ani13132129

Publication

Animals : an open access journal from MDPI
ISSN: 2076-2615
NlmUniqueID: 101635614
Country: Switzerland
Language: English
Volume: 13
Issue: 13

Researcher Affiliations

Medill, Sarah A
  • Department of Biology, University of Saskatchewan, Saskatoon, SK S7N 5C8, Canada.
Janz, David M
  • Department of Veterinary Biomedical Sciences, University of Saskatchewan, Saskatoon, SK S7N 5B4, Canada.
McLoughlin, Philip D
  • Department of Biology, University of Saskatchewan, Saskatoon, SK S7N 5C8, Canada.

Grant Funding

  • 371535-2009 / Natural Sciences and Engineering Research Council
  • 25046 / Canada Foundation for Innovation

Conflict of Interest Statement

The authors declare no conflict of interest.

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