Heart rate variability in Mangalarga Marchador horses after physical exercise

The aim of this study was to evaluate the influence of physical exercise (marcha gait) on heart rate variability indices in Mangalarga Marchador horses. Twenty-five animals, fourteen females and eleven males, aged 6.4 ± 2.7 years and with a mean weight of 428.3 ± 24.7 kg, were used. Electrocardiograms were recorded at two different time points: rest and immediately after exercise (40 min of aerobic exercise, marcha gait). Time domain analyses of heart rate variability were made using vasovagal tonus index (VVTI) and standard deviation of normal intervals (SDNN). Variables were analysed for normality using the Shapiro-Wilk test and comparisons were made between T0 and T1 using the paired t-test (VVTI) or Mann-Whitney (SDNN), considering P < 0.05. The Pearson coefficient was calculated to evaluate the correlation between heart rate and VVTI and the Spearman coefficient was calculated for heart rate and SDNN. There was an increase in heart rate after exercise (P < 0.0001), from 45.7 ± 12.7 to 77.3 ± 13.5 beats/min, and a reduced VVTI (P < 0.0001), from 8.66 ± 1.45 to 4.65 ± 1.25 and a reduced SDNN (P < 0.0001), from 80.09 to 11.67 ms. No correlation was observed between heart rate and VVTI or SDNN. It was possible to conclude that the physical activity carried out by Mangalarga Marchador horses influenced the autonomic response and consequently heart rate variability indexes, suggesting the possible use of these indices for the evaluation of Mangalarga Marchador performance.