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Marc, M., Parvizi, N., Ellendorff, F., Kallweit, E., & Elsaesser, F. (2000). Plasma cortisol and ACTH concentrations in the warmblood horse in response to a standardized treadmill exercise test as physiological markers for evaluation of training status. J. Anim Sci., 78(7), 1936–1946.
Abstract: Reliable physiological markers for performance evaluation in sport horses are missing. To determine the diagnostic value of plasma ACTH and cortisol measurements in the warmblood horse, 10 initially 3-yr-old geldings of the Hannovarian breed were either exposed to a training schedule or served as controls. During experimental Phase 1, horses were group-housed, and half of the horses were trained for 20 wk on a high-speed treadmill. During Phase 2, groups were switched and one group was trained for 10 wk as during Phase 1, whereas the control group was confined to boxes. During Phase 3 horses were initially schooled for riding. Thereafter, all horses were regularly schooled for dressage and jumping, and half of the horses received an additional endurance training for 24 wk. During all phases horses were exposed at regular intervals to various standardized treadmill exercise tests. During and after the tests frequent blood samples were taken from an indwelling jugular catheter for determination of ACTH and cortisol. Treadmill exercise increased both hormones. Maximum ACTH concentrations were recorded at the end of exercise, and maximum cortisol levels were recorded 20 to 30 min later. Except for one test there were no differences in ACTH levels between trained horses and controls. There was no significant effect of training on the cortisol response (net increase) to treadmill exercise in any of the tests during Phase 1. During Phase 2 higher cortisol responses were recorded in controls than in trained horses (P < .05) after 10 wk of training (controls confined to boxes). During Phase 3 plasma cortisol responses were also higher in controls than in trained horses (P < .05 after 6, 18, and 24, P < or = .07 after 12 wk of training) when the inclination of the treadmill was 5%, but not at 3%. There was no overlap in net cortisol responses at 30 min between trained and untrained horses. An ACTH application after 24 wk of training resulted in higher cortisol responses in controls than in trained horses (P < or = .05), without any overlap between the groups at 30 min after ACTH. Plasma cortisol responses to either treadmill exercise or ACTH injection may be a reliable physiological marker for performance evaluation. Prerequisites are sufficient differences in training status and sufficient intensity of exercise test conditions.
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Elsaesser, F., Klobasa, F., & Ellendorff, F. (2001). ACTH stimulation test for the determination of salivary cortisol and of cortisol responses as markers of the training status/fitness of warm-blooded sports horses]. Dtsch Tierarztl Wochenschr, 108(1), 31–36.
Abstract: Previous work (Marc et al., 2000) suggested that plasma cortisol responses to treadmill exercise or ACTH injection are a reliable marker for performance evaluation in warmblood horses. For practical purposes blood sample collections and treadmill exercise tests are somewhat troublesome and time consuming. The goal of this study was thus to evaluate the use of saliva for cortisol determination (by direct EIA) as a marker for performance and to investigate the reliability and repeatability of plasma cortisol responses to a single i.v. injection of ACTH (50 micrograms or 250 micrograms). Furthermore, the effect of training horses for 8 weeks 3 times per week covering the same distance (increasing from 3.5 km during the first week to 8 km during the last week) either by trotting (approximately 240 m/min) or by cantering (375 m/min) was investigated. For this purpose initially ten four-year-old Hannovarian geldings, all reared in the same State stud, were used. Mean overall correlation between salivary cortisol and plasma cortisol concentrations was 0.64 when samples of various points of time were used. However, in spite of attempts to standardize saliva sample collection, correlation between salivary cortisol levels and plasma cortisol levels at distinct points of time in different tests were low and significant (r = 0.85, p < 0.02) only in one test. Thus, salivary cortisol measurements for diagnostic purposes are not reliable 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 < or = 0.01 and p < or = 0.05 respectively). Training horses either by trotting or cantering did not affect the cortisol response either to treadmill exercise or to stimulation by ACTH. It is concluded that the relationship between salivary cortisol levels and plasma cortisol levels is not close enough to allow the use of salivary cortisol determination as marker of the training status/fitness of horses. The repeatability of the cortisol response to ACTH is similar to the cortisol response to treadmill exercise. Based on plasma cortisol responses to ACTH or treadmill exercise training horses by cantering at low speed is not superior to training by trotting for the fitness of horses.
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