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


OBJECTIVE
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.


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. T(3), T(4), fT(3), fT(4) 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 T(4) changes over the sessions (P < 0.05) were recorded. After warm-up, T(4) concentration results were lower than basal in Session 1 (P < 0.05). Higher than basal values were recorded 30 min post exercise for T(3) (P < 0.001), T(4) and fT(4) (P < 0.01) in Session 2 and for T(4) (P < 0.05) and fT(4) (P < 0.01) in Session 3. The interaction fence height/time results were significant on T(3) (P < 0.03) and fT(4) (P < 0.03); sampling time on T(3) (P < 0.0007), T(4) (P < 0.001) and fT(4) (P < 0.002) post exercise changes.


CONCLUSIONS
Showjumping over the highest fences induced a release of T(3) from skeletal muscle, probably due to 5'-desiodase activity and increase of fT(4), due to thyroid stimulation and/or changes in capacity to bind iodothyronines.
Department of Morphology, Biochemistry, Physiology and Animal Production, Unit of Veterinary Physiology, Faculty of Veterinary Medicine, Polo Universitario Annunziata, University of Messina, Messina, Italy. ferlazzo@unime.it
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Ferlazzo
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Medica
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Cravana
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Fazio
D000818:Animals; D018592:Cross-Over Studies; D006339:Heart Rate; D006736:Horses / Q000097:blood*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*
D014284:Triiodothyronine; D013974:Thyroxine