Beyond cortisol: evaluating serotonin, brain-derived neurotrophic factor, and oxytocin as indicators of equine welfare across three training regimens.

Overview

1. Institute of Animal Sciences, Department of Animal Breeding, Warsaw University of Life Sciences (SGGW), Nowoursynowska 166, Warsaw, 02-787 Poland
2. Institute of Veterinary Medicine, Department of Large Animal Diseases and Clinic, Warsaw University of Life Sciences (SGGW), Nowoursynowska 166, Warsaw, 02-787 Poland

Abstract

Background: Quantifying the balance between workload, stress, and recovery across equine disciplines remains challenging, and no single circulating biomarker provides a definitive index of welfare-related stress load. Cortisol, oxytocin, serotonin (5-hydroxytryptamine, 5-HT), and brain-derived neurotrophic factor (BDNF) may provide complementary information on endocrine and neuromodulatory responses.

Methods: Paired serum samples were collected from show jumping horses (n = 17) before and after competition, racehorses (n = 43 enrolled, n = 41 analyzed) before and after sessions at season start (T1), mid-season (T2), and race day (R), and leisure horses (n = 14) at rest before and after the riding season. Biomarkers were quantified by ELISA. Changes were modeled as the natural logarithm of the post/pre ratio [ln(post/pre)] using intercept-only linear models (show jumping, leisure) and linear mixed-effects models for racehorses with horse as a random intercept and session, sex, and breed as fixed effects.

Results: In show jumping horses, 5-HT decreased after competition (post/pre ratio 0.634, 95% CI 0.490–0.820, p = 0.002). Breed-adjusted estimates supported a 5-HT decrease in mares (0.470, p = 0.026) and a BDNF increase in geldings (1.727, p = 0.021). In racehorses, 5-HT increased on race day in mares (1.948, 95% CI 1.258–3.015, p = 0.003) and stallions (2.207, p < 0.001) and did not differ from a post/pre ratio of 1.0 after T1 or T2. BDNF and oxytocin remained close to a post/pre ratio of 1.0 across race sessions (all p ≥ 0.507). Cortisol showed no significant session-specific changes, with lower post/pre ratios in stallions that did not reach statistical significance during T2 and race day (p = 0.059 and p = 0.064). Leisure horses showed no significant changes across the riding season for any marker (all p ≥ 0.166).

Conclusions: Serotonin exhibited the strongest discipline-dependent responsiveness, with opposite directions of change after show jumping competition and on race day. BDNF responses were restricted to show jumping geldings, whereas oxytocin and cortisol were largely unchanged under the sampling schedule used. Under the applied sampling framework, multi-marker profiling may help characterize discipline-dependent neuroendocrine dynamics, but it does not by itself establish welfare status.

Supplementary Information: The online version contains supplementary material available at 10.1186/s12917-026-05507-7.

Reproduced under the paper's license (CC BY), from the paper cited above.

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Data

Datasets cited

• figshare:32723704, at figshare; found in DataCite
• figshare:32723707, at figshare; found in DataCite
• figshare:32723710, at figshare; found in DataCite

Data availability

Datasets are deposited at https://repod.icm.edu.pl/dataset.xhtml?persistentId=doi:10.18150/IEXY65 RepOD repository.

Reproduced under the paper's license (CC BY), from the paper cited above.

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Version 1, 30 September 2026: the first record

Recorded: type, language, journal, volume, issue, pages, dates, 10 authors, 9 keywords, 12 MeSH terms, 2 funders, 46 references.

Cite

This paper

Kacprzyk, M., Tobolski, D., Kiełbik, P., Grzędzicka-Agko, J., Milczek-Haduch, D., Stefanik, E., Dąbrowska, I., Pawliński, B., Gołębiewski, M., & Witkowska-Piłaszewicz, O. (2026). Beyond cortisol: evaluating serotonin, brain-derived neurotrophic factor, and oxytocin as indicators of equine welfare across three training regimens. BMC veterinary research, 22(1), 355. https://doi.org/10.1186/s12917-026-05507-7

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