Training- and competition-related changes on circulating adrenocorticotropic hormone and cortisol response in...

Exercise is a physiological challenge inducing intensity-dependent hypothalamic-pituitary-adrenal (HPA) axis responses. The hypothesis was that training and racing sessions induce different HPA axis activation.

To assess whether different exercise sessions affect equine adrenal responsiveness according to age and sex.

Ten clinically healthy Thoroughbred racehorses (6 females and 4 males) were recruited. Four were 2 years old and six were 3 years old. Horses were subjected to two exercise conditions: training and competitive racing sessions. Blood samples were collected at rest and at 5- and 30-min post-exercise to assess circulating adrenocorticotropin (ACTH) and cortisol changes. To determine the effects of exercise, age, and sex on hormonal responses over baseline values, one-way analysis of variance (ANOVA) was applied.

Compared to baseline concentrations, ACTH and cortisol concentrations increased at 5 and 30 min (P < .001) after both training and racing sessions. Compared with training, racing horses had greater ACTH increases at baseline (Δ% 64) and 5 min (Δ% 110), and 30 min (Δ% 283) post-exercise. Cortisol concentrations increased more after racing than training at 5 min (Δ% 89) and 30 min (Δ% 128).

Results showed that training and competitive racing differentially affected the HPA axis response, with a potential preparatory or anticipatory reaction to exercise before racing.