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Home / Equine Research Bank / J Vet Intern Med / The Effect of Season and Breed on Hypothalamic-Pituitary-Adr...
Journal of veterinary internal medicine2025; 39(2); e70047; doi: 10.1111/jvim.70047

The Effect of Season and Breed on Hypothalamic-Pituitary-Adrenal Axis Hormones, Metabolic Hormones, and Oxidative Markers in Ponies and Horses.

Abstract: Endocrine function in ponies differs from horses, with seasonally increased concentrations of plasma adrenocorticotropic hormone (ACTH) and an increased risk of insulin dysregulation. Objective: (1) Season and breed differences exist in concentrations of hypothalamic-pituitary-adrenal axis and metabolic hormones; and (2) systemic oxidative status is significantly different between ponies and horses and correlates with endocrine hormones. Methods: Thirty-four healthy Welsh ponies and 14 healthy Quarter horses. Methods: Blood was collected from Welsh ponies and Quarter horses in the same region during the same weeks in May and October. Concentrations of plasma ACTH, insulin, leptin, derivatives of reactive oxygen metabolites (dROMs), plasma antioxidant capacity (PAC), and serum total cortisol, percent-free cortisol, and estimated free cortisol concentrations were measured. Linear mixed effects modeling with a random effect for animal was used to determine the effects of season and breed. Correlation coefficients were calculated for relevant variables. Statistical significance was set at p < 0.05. Results: Fall plasma ACTH concentration was significantly higher in ponies compared with horses (p < 0.001). Total cortisol concentration was significantly lower in ponies in fall compared with spring (p = 0.05; 95% confidence interval [CI] = 0.005-0.934). Insulin concentrations in ponies were significantly higher in fall compared with spring (p < 0.001) and compared with horses in fall (p < 0.001). In horses, PAC was higher in fall than in spring (p = 0.01; 95% CI = -730.2T to -99.26). Correlations varied with season and breed. Conclusions: Season and breed significantly affect the HPA axis, metabolic hormones, and oxidative status. Our results support breed consideration when interpreting endocrine testing results in horses.
© 2025 The Author(s). Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.
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Publication Date: 2025-03-06 PubMed ID: 40048369PubMed Central: PMC11884412DOI: 10.1111/jvim.70047Google 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 examines the effects of season and breed on various hormones and oxidative markers in ponies and horses. The study found significant differences in hormone concentrations and oxidative status between Welsh ponies and Quarter horses, with these differences varying across different seasons.

Research Objectives

  • The research aimed to determine whether there are differences in the concentrations of hypothalamic-pituitary-adrenal (HPA) axis and metabolic hormones between different seasons and breeds.
  • The study also aimed to understand whether the systemic oxidative status differs between ponies and horses and if this correlates with endocrine hormones.

Methodology

  • The researchers selected 34 healthy Welsh ponies and 14 healthy Quarter horses for the study.
  • Blood samples were taken from these animals during the same weeks in May and October in the same region.
  • The concentrations of various hormones and derivatives, such as plasma adrenocorticotropic hormone (ACTH), insulin, leptin, derivatives of reactive oxygen metabolites (dROMs), plasma antioxidant capacity (PAC), and serum total cortisol, were measured.
  • Statistical methods like linear mixed effects modeling were applied, with a random effect for the animal to find the impacts of the season and breed. Correlation coefficients for relevant variables were calculated with statistical significance set at p < 0.05.

Results

  • The study found that in fall, the concentration of plasma ACTH was significantly higher in ponies compared to horses. Moreover, in ponies, the total cortisol concentration was significantly lower in fall compared to spring.
  • Insulin concentrations in ponies were significantly higher in fall compared with spring, and also higher than those in horses during fall.
  • In horses, the plasma antioxidant capacity (PAC) was higher in fall than in spring.
  • The correlations varied with season and breed, highlighting the affect they can have on hormone concentrations and oxidative status.

Conclusions

  • The research concluded that both season and breed have significant effects on the HPA axis, metabolic hormones, and oxidative status in horses and ponies.
  • The results suggest that breed should be taken into consideration when interpreting endocrine testing results in horses.

Cite This Article

APA
Vaughn SA, Lemons MB, Hart KA. (2025). The Effect of Season and Breed on Hypothalamic-Pituitary-Adrenal Axis Hormones, Metabolic Hormones, and Oxidative Markers in Ponies and Horses. J Vet Intern Med, 39(2), e70047. https://doi.org/10.1111/jvim.70047

Publication

Journal of veterinary internal medicine
ISSN: 1939-1676
NlmUniqueID: 8708660
Country: United States
Language: English
Volume: 39
Issue: 2
Pages: e70047
PII: e70047

Researcher Affiliations

Vaughn, Sarah Alison
  • University of Georgia, Department of Large Animal Medicine, Athens, USA.
Lemons, Margaret B
  • University of Georgia, Department of Large Animal Medicine, Athens, USA.
Hart, Kelsey A
  • University of Georgia, Department of Large Animal Medicine, Athens, USA.

MeSH Terms

  • Horses / physiology
  • Horses / blood
  • Animals
  • Adrenocorticotropic Hormone / blood
  • Hypothalamo-Hypophyseal System / metabolism
  • Pituitary-Adrenal System / physiology
  • Seasons
  • Hydrocortisone / blood
  • Male
  • Insulin / blood
  • Female
  • Leptin / blood
  • Oxidative Stress
  • Biomarkers / blood
  • Reactive Oxygen Species / blood

Grant Funding

  • D20EQ-035 / Morris Animal Foundation

Conflict of Interest Statement

Dr. Kelsey Hart has served as an unpaid consultant for and had travel expenses covered by Boehringer Ingelheim, producer of a Food and Drug Administration (FDA) labeled treatment for pituitary pars intermedia dysfunction in horses. She was not involved in the selection of animals for sampling. Classification of animals was decided using the published consensus statement's recommended cut‐off values. The other authors declare no conflicts of interest.

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