Effects of fence height on total and free iodothyronine changes in horses after experimental show jumping sessions

Summary Reasons for performing study: Involvement of thyroid function on performance warrants further investigation as limited data exists on the effects of showjumping on the dynamics of total and free iodothyronines. Objectives: To investigate the response of circulating total and free iodothyronines in horses to experimental showjumping sessions and compare with the effects normally induced by competition and determine if fence height has any effect. Materials and methods: Using a randomised crossover study design 6 trained horses were studied during experimental showjumping sessions over 10 fences of different height: 1.00 m (Session 1), 1.10 m (Session 2), 1.20 m (Session 3). Hormone levels were recorded before, after warm‐up, 5 and 30 min post exercise. T3, T4, fT3, fT4 concentrations were analysed by ELISA/competition using streptavidin technology. RM‐ANOVA was applied to test for any differences in basal and warm‐up values of different sessions. Two way RM‐ANOVA was applied to test for any effects of interaction between fence height and time. The differences between individual means over time were assessed using a post hoc multiple comparison test (Bonferroni). Results: Basal T4 changes over the sessions (P