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, 12 (9), e0182257
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Low Plasma Cortisol and Fecal Cortisol Metabolite Measures as Indicators of Compromised Welfare in Domestic Horses (Equus Caballus)

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Low Plasma Cortisol and Fecal Cortisol Metabolite Measures as Indicators of Compromised Welfare in Domestic Horses (Equus Caballus)

Jodi Pawluski et al. PLoS One.

Abstract

The hypothalamic-pituitary-adrenal (HPA) axis response to chronic stress is far from straight forward, particularly with regards to animal welfare. There are reports of no effect as well as both decreases and increases in cortisol after chronic stressors. Therefore, the first aim of the present study was to determine how measures of compromised welfare, such as chronic pain and haematological anomalies, related to cortisol levels in domestic horses (Equus caballus). Domestic horses are an informative model to investigate the impact of chronic stress (due to environment, pain, work, housing conditions…) on the HPA axis. The second aim was to determine whether levels of fecal cortisol metabolites (FCM) may be used as an indicator of welfare measures. The present study used fifty-nine horses (44 geldings and 15 mares), from three riding centres in Brittany, France. The primary findings show that horses whose welfare was clearly compromised (as indicated by an unusual ears backward position, presence of vertebral problems or haematological anomalies, e.g. anaemia) also had lower levels of both FCM and plasma cortisol. This work extends our previous findings showing that withdrawn postures, indicators of depressive-like behavior in horses, are associated with lower plasma cortisol levels. We also found that evening plasma cortisol levels positively correlated with FCM levels in horses. Future research aims to determine the extent to which factors of influence on welfare, such as living conditions (e.g. single stalls versus group housing in pasture or paddocks), early life factors, and human interaction, act as mediators of cortisol levels in horses.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. A) Mean (+SEM) plasma cortisol levels in horses.
Plasma cortisol concentrations were significantly lower in the evening, both after a day’s work and after a day’s rest, than in the morning (p < 0.00001, N = 55–56). B) Average evening plasma cortisol levels and average levels of fecal cortisol metabolites were significantly correlated (r = 0.66, p<0.0001, N = 55). * denotes a significant difference.
Fig 2
Fig 2. Mean (+SEM) average fecal cortisol metabolite levels after work as a function of ear position in horses.
(A). Horses with mostly the backward ear position had significantly lower average fecal cortisol measures after work (p = 0.04). Time horses spent with ears in a backwards position was negatively correlated with average evening (B) FCM (p = 0.02) and (C) plasma cortisol measures (p = 0.04). (A) Forward ears N = 19, Backward ears, N = 31; (B) N = 59, (C) N = 55.
Fig 3
Fig 3. Mean (+SEM) cortisol measures related to measures of welfare in horses.
A) Horses with severely affected vertebral problems had significantly lower evening plasma cortisol levels compared to totally exempt or slightly affected horses (p = 0.02; severely affected horses (n = 40) vs slightly affected horses (n = 15)). B) Anaemic horses had significantly lower evening plasma cortisol concentrations compared to non-anaemic horses (p = 0.02; anaemic horses = 10, non-anaemic horses = 45). C) Horses with levels of neutrophils outside the norm had significantly lower FCM levels compared to horses with normal neutrophil levels (p = 0.03; unusual neutrophils = 19, normal neutrophils = 36). D) Horses with ‘compromised’ global welfare had significantly lower evening plasma cortisol levels compared to ‘normal’ horses (p = 0.001; compromised = 13, normal = 17).). *denotes significant main effect, regardless of day of rest or work.

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Grant support

This work was funded by the Caisse Centrale de la Mutualité Agricole, University of Rennes 1 and the Le Centre national de la recherche scientifique (CNRS). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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