Elite sport horses, expected to perform at the top of their game, appear to be no more affected by stress than their amateur counterparts, research findings suggest.
Their top-tier status does not appear to have any long-term adverse consequences in terms of their welfare, based on their reactivity to the stress hormone cortisol.
However, the Swiss scientists who carried out the research found several factors that did affect the amount of cortisol released in a standardized test.
Fay Sauer and her colleagues, writing in the open-access journal PLOS ONE, found that Thoroughbred and Warmblood horses had a heightened adrenal response compared to Franches-Montagnes horses.
Horses with several riders had a less pronounced stress reaction than horses with one rider, as did horses that spent more time outside when compared to horses that were stabled most of the time.
Horses living in groups showed higher post-stimulatory cortisol values than horses that were housed singly.
However, the study team found no significant associations of cortisol responsiveness with personality traits. Nor did the horse’s discipline have an effect on their cortisol response.
“This suggests that optimizing husbandry conditions may be more important for improving equine welfare than changing their use,” they said.
For their study, the researchers visited 94 healthy elite sport horses and 54 amateur counterparts in Switzerland.
They performed what is known as an adrenocorticotropic hormone stimulation test. This is a test that measures how well the adrenal glands respond to adrenocorticotropic hormone. This hormone, produced in the pituitary gland, stimulates the adrenal glands to release cortisol.
Salivary cortisol concentrations were measured 60 and 90 minutes after stimulation, with levels at the 60-minute mark considered most informative as a measure of the long-term effects of stress.
Additionally, a person familiar with each horse completed a questionnaire about demographic and management factors, and their horses’ personality traits.
The authors say their work is the first known study to compare the stress of high-performance athletes with amateur sport horses, with no difference found in post-stimulatory cortisol levels between the two groups.
“However, studies investigating acute stress in relation to training and competition showed that experienced horses had lower basal plasma cortisol values than inexperienced horses. Furthermore, horses with a superior physical training level had decreased basal cortisol levels, indicating that trained horses experience less stress during exercise than untrained horses.”
Potentially, they said, the increased requirements and the elevated stress levels that elite sport horses encounter may be compensated by their greater experience, their better fitness, and possibly by their more professional riders.
“This may be the reason why measurable indicators of long-term stress, such as cortisol responsiveness to external stimulation, do not differ between elite and amateur sport horses.”
The researchers said it was interesting that horses with two, three, or more riders had a less pronounced adrenal response than horses with only one rider.
“Conceivably, horses that are accustomed to higher levels of stimulation in everyday life may be better equipped to deal with challenging situations.”
Horses that spent more time outside of their stalls on pasture or for training and competition had a decreased stress reaction, in line with previous studies indicating better welfare in pastured horses compared to stalled horses.
The researchers found that horses living full-time in groups and horses living in groups on pasture showed higher post-stimulatory cortisol values than single-housed horses.
“Contradictory results have been reported in previous studies investigating stress levels of domestic horses in different types of housing,” they noted.
“Although group housing appears overall to have beneficial effects on horse welfare, it is also associated with social challenges, which might be reflected by the increased cortisol reactivity of group-housed horses in the present study.
“In this context,” they said, “social stability of groups might be important to consider in future studies.”
The full study team comprised Sauer, Marco Hermann, Alessandra Ramseyer, Dominik Burger, Stefanie Riemer, and Vinzenz Gerber, from a range of Swiss institutions.
Sauer FJ, Hermann M, Ramseyer A, Burger D, Riemer S, Gerber V (2019) Effects of breed, management and personality on cortisol reactivity in sport horses. PLoS ONE 14(12): e0221794. https://doi.org/10.1371/journal.pone.0221794