Plasma cortisol concentration in Thorougbred horses during and after standardized exercise tests on a treadmill and effect of conditioning on basal cortisol values

Abstract

SummaryThe behaviour of cortisol concentration in plasma of clinically normal horses performing two different exercise tests on a treadmill was investigated to study the possible value of measuring cortisol for performance diagnosis. In addition, the horses were exercised with different conditioning programmes and their effect on basal plasma cortisol concentration was measured. Finally, the repeatability of the cortisol values measured before and after exercise were examined. Horses were always exercised on a treadmill. The multiple step exercise test consisted of five gallop workouts lasting five minutes´ each. The velocity in the first step was 6.0 m/s. Each consecutive step velocity was increased by 0.5 m/s. The two-speed exercise test consisted of two runs. In the first run horses were galloped over 1,200 m at a constant velocity of 10, 10.5 or 11 m/s. Thereafter horses were walked for 30 minutes. The second run over 1,200 m was conducted at speeds of 13, 13.5 or 14 m/s. Each conditioning programme examined 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. During the multiple step test the mean cortisol concentration in plasma showed a tendency to increase (p = 0.07). The mean peak of the cortisol concentration in plasma was measured 10 minutes after the test. Thereafter mean cortisol concentration continuously decreased and the day after the test values were similar to those before the test. After the first run of the two-speed test mean plasma cortisol concentration tended to increase (p = 0.08), while significant changes were registered after the second run (p < 0.01): It decreased up to the fifth minute after exercise (p < 0.05) and increased threreafter reaching a plateau between the 15th and 45th minute after exercise (p < 0.05). The morning after the test mean plasma cortisol concentration had returned to the values measured the morning before the test. None of the conditioning programmes had an effect on the mean plasma concentration of cortisol in the horses at rest. The mean coefficient of variation of plasma cortisol concentration in five horses before exercise was 34.1% and 36.4% after exercise. The large individual variability of plasma cortisol concentrations before and after exercise does not allow a good repeatability of results, and enforces the need for multiple blood sampling during exercise. The multiple step exercise test as well as the two-speed exercise test induced increases of the plasma cortisol concentration after exercise. The changes measured supply a basis for studies on treadmills on the value of monitoring the plasma cortisol concentration of sport horses for performance diagnosis. Keywords:horse, exercise, cortisol, blood plasma, lactate

Effects of competition experience and transportation on the adrenocortical and thyroid responses of horses

“…Similar increases in cortisol concentrations have been observed after exercise in standardbred and thoroughbred trained horses (Lindner and others 2000, 2002) and in show jumpers (Covalesky and others 1992, Ferlazzo and Fazio 1997) and appear to be related to the type, duration and intensity of the exercise (Linden and others 1990, 1991, Desmecht and others 1996, Golland and others 1996, Nagata and others 1999, Marc and others 2000, Ferlazzo and others 2007). The significant increases in cortisol concentration in all four groups appeared to be related more to the show jumping competition than to the stress of transport, although increases in cortisol have been identified as an indicator of transport stress in horses (Clark and others 1993, Smith and others 1996).…”

Endocrine changes after experimental showjumping

“…After the warm-up, the horses walked for 10 min until the heart rate decreased to , 50 beats min 21 . The jumping sessions were performed after a warm-up.…”

“…It is well known that the cortisol response usually depends on the state of individual fitness and training 17,[20][21][22] . Moreover, training may produce a more rapid decline in cortisol levels after exercise towards resting values 2 , while overtraining has been associated with a reduction in the cortisol response to exercise 23,24 .…”

Influence of training and competitive sessions on peripheral β-endorphin levels in training show jumping horses

“…Blood lactate measurements are determined during the training sessions with a hand-held portable lactate analyzer (Accusport) allowing immediate adjustments to training intensities and work prescription for individual horses. Moreover, blood lactate determination as a measure of aerobic-anaerobic threshold has been found to be useful for assessing fitness, running ability, and racing performance in equine athletes [ 17 , 20 , 21 ].…”