Is the thoroughbred race-horse under chronic stress?

The research aims to determine if thoroughbred racehorses, particularly young fillies, are under chronic stress, which is assessed through the analysis of cortisol levels in their blood.

Research Design and Methodology

• For this study, the researchers divided thoroughbred fillies into three groups according to their age. Group 1 included seven fillies between 1 and 2 years old just starting their training program. Group 2 consisted of nine fillies aged 2 to 3 years, who were involved in an extensive training program. Group 3 composed of eight fillies from 3 to 4 years of age, both training and currently racing.
• Blood samples were collected from all these horses weekly over a span from July to December.
• These samples were analyzed for cortisol levels using a solid-phase DPC kit. Cortisol is a hormone released in response to stress and low blood glucose concentration.

Summary of Findings

• The cortisol levels varied across the groups – The average cortisol levels for the semester in Group 1, Group 2, and Group 3 were 148.8 +/- 6.7, 125.7 +/- 5.8, and 101.1 +/- 5.4 nmol/l, respectively. This index indicates that Group 3, the older, racing fillies, had significantly lower cortisol levels than the others.
• The researchers proposed that the stress stimulus, sustained over a long period, may become chronic for these horses and could result in a reduction of the receptors in the brain that respond to the corticotropin-releasing hormone from the pituitary gland. This could potentially explain the lower cortisol levels in the older fillies.
• In addition to this, the researchers also suggested that the release of endogenous opioids, which are the body’s naturally occurring painkillers, could be another reason for the diminished serum cortisol levels.

Conclusion

• The observed reduced cortisol levels in older fillies under chronic training and racing conditions suggest that these horses could indeed be in a state of chronic stress, which may pose concerns for their health and overall well-being.