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PloS one2023; 18(4); e0284102; doi: 10.1371/journal.pone.0284102

Variation in salivary cortisol responses in yearling Thoroughbred racehorses during their first year of training.

Abstract: Thoroughbred horses are bred for competitive racing and undergo intense training regimes. The maintenance of physical soundness and desirable behavioural characteristics are critical to the longevity of a racing career. Horses intended for Flat racing generally enter training as yearlings and undergo introductory training prior to exercise conditioning for racing. This period requires rapid adjustment to a novel environment. As a prey animal, a horse's 'fight-or-flight' response is highly adapted, in which a well-understood component of this response, the hypothalamic-pituitary-axis, is activated in response to a stress stimulus, releasing cortisol. In the Thoroughbred, a significant difference in salivary cortisol concentrations between pre- and post-first time ridden (i.e., first backing) by a jockey have previously been identified. Here, to test the hypothesis that salivary cortisol concentrations may be used to objectively detect individual variations in the acute physiological stress response we investigate individual variation in cortisol response to training milestones. Saliva samples were collected from a cohort of n = 96 yearling Flat racehorses, at the same training yard, across three timepoints at rest: before entering the training yard (n = 66), within three days of entry to the training yard (n = 67) and following 2-3 weeks in the training yard (n = 50). Salivary cortisol concentration was measured using an ELISA. There was no significant difference in cortisol concentration (ANOVA, P > 0.05) across the samples collected at timepoints at rest. Samples were also collected before and 30 minutes after exposure to three novel training events: first time long-reined (n = 6), first time backed by a jockey (n = 34), and first time ridden on the gallops (n = 10). Mean salivary cortisol concentration after all three novel training events was significantly higher than prior to the training event (Paired t-test, P <0.005). The ranges of post-event salivary cortisol concentration across all timepoints suggest individual variation in the measured stress response, reflecting individual differences in stress response to the early training environment. This measure may be used as an objective assessment of the stress response of Thoroughbred racehorses during training.
Copyright: © 2023 Holtby et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Publication Date: 2023-04-06 PubMed ID: 37023093PubMed Central: PMC10079128DOI: 10.1371/journal.pone.0284102Google 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 explores the variation in stress responses of young Thoroughbred racehorses during their first year of training, using salivary cortisol levels as a measure. The aim is to objectively assess individual horses’ physiological responses to novel situations and events.

Background

  • Thoroughbred racehorses endure intense training regimes right from their early years. Maintaining their physical and behavioural wellbeing is important for a successful racing career.
  • As part of an adaptive ‘fight-or-flight’ response to stress, horses produce cortisol hormone, measurable in their saliva.
  • Prior studies showed significant differences in cortisol concentrations before and after the horses’ first ride by a jockey, known as ‘first backing’.
  • The researchers aimed to further study these cortisol responses to better understand individual variations in stress response.

Methodology

  • The study used a total of 96 yearling racehorses at a single training yard. Saliva samples were collected at various stages: before entering the training yard, within the first three days of entering the yard, and after 2-3 weeks in the yard.
  • Cortisol concentrations in the samples were measured using an assay test.
  • Saliva samples were also gathered before and half an hour after each of three novel training events: first-time long-reined, first-time ridden by a jockey, and first-time ridden on the gallops.

Findings

  • No significant difference in cortisol concentration was observed across the resting samples collected at different timepoints.
  • The cortisol concentration after all three novel training events was significantly higher, showing the horses’ physiological stress response.
  • The variations in post-event cortisol concentrations suggest that horses respond differently to early training environments and have individualized stress responses.

Significance

  • The findings present a new method for assessing racehorses’ stress responses to training using objective measures, which could potentially be useful in optimizing training regimes and improving the wellbeing and performance of the horse.

Cite This Article

APA
Holtby AR, McGivney BA, Browne JA, Katz LM, Murphy KJ, Hill EW. (2023). Variation in salivary cortisol responses in yearling Thoroughbred racehorses during their first year of training. PLoS One, 18(4), e0284102. https://doi.org/10.1371/journal.pone.0284102

Publication

PloS one
ISSN: 1932-6203
NlmUniqueID: 101285081
Country: United States
Language: English
Volume: 18
Issue: 4
Pages: e0284102

Researcher Affiliations

Holtby, Amy R
  • UCD School of Agriculture and Food Science, University College Dublin, Belfield, Dublin, Ireland.
  • Plusvital Ltd., The Highline, Dun Laoghaire, Co. Dublin, Ireland.
McGivney, Beatrice A
  • Plusvital Ltd., The Highline, Dun Laoghaire, Co. Dublin, Ireland.
Browne, John A
  • UCD School of Agriculture and Food Science, University College Dublin, Belfield, Dublin, Ireland.
Katz, Lisa M
  • UCD School of Veterinary Medicine, University College Dublin, Belfield, Dublin, Ireland.
Murphy, Keith J
  • UCD Neurotherapeutics Research Group, Conway Institute, UCD School of Biomolecular and Biomedical Science, University College Dublin, Belfield, Dublin, Ireland.
Hill, Emmeline W
  • UCD School of Agriculture and Food Science, University College Dublin, Belfield, Dublin, Ireland.
  • Plusvital Ltd., The Highline, Dun Laoghaire, Co. Dublin, Ireland.

MeSH Terms

  • Horses
  • Animals
  • Hydrocortisone
  • Physical Conditioning, Animal
  • Horse Diseases
  • Running
  • Physical Examination

Conflict of Interest Statement

This research was carried out with the financial support of Plusvital Ltd. Plusvital is an equine nutrition and genetic testing company in which EWH is a shareholder. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

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