Evaluation of salivary cortisol determination and of cortisol responses toACTH as markers of the training status/fitness of warmblood sports horses.

Previous work (Marc et al., 2000) suggested that plasma cortisol responses to treadmill exercise or ACTH injection are a reliable marker for performan ce evaluation in warmblood horses. For practical purposes blood sample coll ections and treadmill exercise tests are somewhat troublesome and time cons uming. The goal of this study was thus to evaluate the use of saliva for co rtisol determination (by direct EIA) as a marker for performance and to inv estigate the reliability and repeatability of plasma cortisol responses to a single i. v. injection of ACTH (50 mug or 250 mug) Furthermore, the effec t of training horses for 8 weeks 3 times per week covering the same distanc e (increasing from 3.5 km during the first week to 8 km during the last wee k) either by trotting (similar to 240 m/min) or by cantering (375 m/min) wa s investigated. For this purpose initially ten four-year-old Hannovarian ge ldings, all reared in the same State stud, were used. Mean overall correlat ion between salivary cortisol and plasma cortisol concentrations was 0.64 w hen samples of various points of time were used. However, in spite of attem pts to standardize saliva sample collection, correlation between salivary c ortisol levels and plasma cortisol levels at distinct points of time in dif ferent tests were low and significant (r = 0.85, p < 0.02) only in one test . Thus, salivary cortisol measurements for diagnostic purposes are not reli able or useful. The repeatability of plasma cortisol responses to ACTH for untrained and trained horses were r = 0.86 and r = 0.8 respectively (p <les s than or equal to> 0.01 and p less than or equal to 0.05 respectively). Tr aining horses either by trotting or cantering did not affect the cortisol r esponse either to tread mill exercise or to stimulation by ACTH. It is conc luded that the relationship between salivary cortisol levels and plasma cor tisol levels is not close enough to allow the use of salivary cortisol dete rmination as marker of the training status/fitness of horses. The repeatabi lity of the cortisol response to ACTH is similar to the cortisol response t o treadmill exercise. Based on plasma cortisol responses to ACTH or treadmi ll exercise training horses by cantering at low speed is not superior to tr aining by trotting for the fitness of horses.