Effects of competition experience and transportation on the adrenocortical and thyroid responses of horses.

The research article examines the impact of competition experience and transportation stress on biochemical responses in horses, specifically focusing on adrenocortical and thyroid hormones. Overall, stress from both competition and transportation triggered a rise in cortisol, a stress hormone, regardless of experience, but did not significantly affect thyroid hormones.

Study Design and Participants

• The study included 63 sport horses broken into four distinct groups. Each group represented a varying combination of competition experience and transportation stress.
• Group 1 was made up of 14 trained, but inexperienced jumper horses. Group 2 comprised of 20 trained and experienced jumper horses. Group 3 included 10 trained, inexperienced jumpers who were transported just before the competition. Lastly, Group 4 consisted of 19 trained, experienced jumpers that were also transported just before the competition.

Measurements and Findings

• The researchers measured the horses’ plasma concentrations of total cortisol, total iodothyronine, and free iodothyronine before and after the competition.
• Results showed a significant increase in cortisol levels, a response often associated with stress, in all four groups both five and thirty minutes after the competition, indicating that competition and transport induce stress in horses, irrespective of their training or past experience.
• However, the levels of thyroid hormones (triiodothyronine, thyroxine, and free thyroxine) did not undergo significant changes after the competition, suggesting that these hormones are not affected by the stressful circumstances of the competition or transport.

Special Observations

• One particular observation was that the horses in group 2 (experienced, no transport stress) had significantly lower basal (basic, resting) levels of free triiodothyronine compared to the horses in the other three groups.
• This difference was maintained at both five and thirty minutes post-competition, indicating a possible stable difference in thyroid activity in relation to competition experience and absence of transport stress. The reason for this difference in thyroid hormone levels warrants further investigation.