No abstract

Results suggested that frequency of EIPH-related epistaxis in racehorses is associated with the horse's age and sex, the type of race, and the distance raced. The higher frequency in shorter races suggests that higher intensity exercise of shorter duration may increase the probability of EIPH.

Results suggest that the likelihood of AF among racehorses that finish slowly is related to age and racing surface.

SummaryWe studied the influence of training on autonomic nervous function in the horse. For this purpose, Holter electrocardiogram (ECG) was recorded before and after training from 24 Thoroughbred horses (2-year-olds) and autonomic nervous function was evaluated by the power spectral analysis of heart rate (HR) variability. We obtained HR, low-frequency (LF) power, high-frequency (HF) power, and LFRIF ratio from recording. We set LF at 0.014.07 Hz and HF at 0.0746 Hz. The HF power is thought to reflect primarily parasympathetic nervous function. Both the sympathetic and parasympathetic nervous systems have been shown to contribute to the LF power. The LF/HF ratio is considered as an index of the cardiac sympathovagal balance. Second degree atrioventricular blocks were found in the ECG of 3 and 5 horses before and after the training period, respectively. Ventricular premature depolarisations were detected in a horse after the training period. Heart rate decreased at night. The lowest HR values had a tendency to appear in the early morning. Both the LF and HF power tended to be higher at night. However, the LFRIF ratio was almost the same throughout the day. The HR was significantly decreased by training. Although the LF power and LF/HF ratio were significantly increased, the HF power was not changed by training. These results suggest that parasympathetic nervous activity may be fully activated even before training in this species.

Summary The responses of plasma adrenocorticotropin (ACTH), cortisol, noradrenaline and adrenaline in 5 Thoroughbred horses to an incremental exercise and 2 relative workload exercises, at 105 and 80% maximal oxygen consumption (V̇O2max), on a treadmill were examined. These hormone concentrations increased (P<.05) with each exercise and the maximal plasma concentrations of ACTH, cortisol were observed between 5 and 30 min after the end of the exercise, while maximal catecholamine concentrations occurred just at exhaustion time. The plasma ACTH, noradrenaline and adrenaline responses during exercise were more sensitive to the intensity of exercise than that of cortisol and showed a significant correlation with blood lactate concentrations (r=0.605, P<.001 for ACTH; r=0.718, P<.001 for noradrenaline; r=0.738, P<.001 for adrenaline). The plasma cortisol response appeared to be connected with the duration of exercise (r=0.71, P<.05). The recovery of these hormones was related to the exercise styles. These results suggest that the autonomic nervous system and the pituitary‐adrenal axis of the horse are efficiently stimulated by various treadmill exercises, and these hormones may be used in the evaluation of exercise‐induced stress.