Coefficient of variation of and effect of conditioning on concentration of plasma total and free lodothyronines in Thoroughbred horses

The coefficient of variation of T4, fT4, T3, and fT3, concentrations in blood plasma of horses before and after exercise was determined. In addition, the effect of six different conditioning programs on plasma T4, fT4, T3, and fT3, concentration of five Thoroughbred horses was studied in a latin square cross over study design. Each conditioning programme consisted of eleven repetitions of exercise of 5, 15 or 25 minutes' duration at a velocity at which, mathematically, horses had a blood lactate concentration of 2.5 or 4 mmol/l. The mean coefficient of variation before exercise was 11.4%, 13.8%, 9.8%, and 20.0%, for T4, fT4, T3, and fT3, and 19.9%, 17.3%, 9.7% and 9.9% after exercise. None of the conditioning programmes had an effect on plasma concentration of thyroid hormones.