Effects of show jumping competition plus transport stress on total and free iodothyronine changes of sport horses

Thyroid hormones are considered as a marker of stress in sport horses, showing changes in according to training, exercise and transport. The aim of research was to studied the total and free iodothyronine changes of No. 6 jumping horses (7‐12 years old), performed in show jumping competition, after competition, after pre - competition and post‐competition transport, and after competition plus transport. Blood samples were collected in basal conditions, before and after transport, before exercise, and 5 and 30 minutes after exercise. Serum total and free iodothyronine concentrations were analysed using commercial immunoenzymatic assays (EIA, RADIM, Rome, Italy). A 1-way repeated measure analysis of variance was applied to test the effects of competition, transport and competition plus transport on basal values. Compared to basal values, no significant changes were observed for total and free iodothyronines both after pre‐competition, post‐competition transport and post‐competition plus transport. Post‐competition transport basal T3 values were higher (P<0.01) than pre‐competition transport basal values, and post-competition transport basal fT4 values were lower (P<0.01) than pre‐competition transport basal values. A significant effect of competition on fT3 changes (F=4.227; P<0.05) was recorded. Competition plus transport basal T3 values were higher (P<0.001) than competition basal values, while competition plus transport basal fT3 values were lower (P<0.001) than competition basal values. Results obtained showed that transport and show jumping competition differently influenced the thyroid responses of trained sport horses to physiological and psychological stress, also on dependence of jumpers’ recovery period and individual performance. The increase of total and free iodothyronines after transport confirmed previous data observed in sport horses after short road transport, showing that T3 represents the hormonal metabolic active form in response to stressful stimuli (1,2). The lowest basal fT4 concentration after competition plus transport showed the effect of additional physical effort and that the recovery period was probably inadequate. The highest basal T3 and the lowest fT3 values of horses submitted to transport plus exercise showed their primary involvement in maintaining functional homeostasis after competitive exercise. In addition, no significant changes of total and free iodothyronines 5 and 30 min after competition confirmed previous data observed in experienced jumpers submitted to transport before exercise.