Cardiac Changes after Lactate-Guided Conditioning in Young Purebred Arabian Horses

Figures

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  Figure 1. Experiment timeline. The naïve horses were housed at the university and submitted to rational taming. During this period, the experimental procedures were carried out. The incremental exercise test (IET) was performed before and after six weeks of conditioning. The echocardiographic images were obtained before and after the 5.5 month interval, including the conditioning period. M, month; D, day; W, week.

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  Figure 2. Schematic representation of the incremental exercise test (IET). The IET was performed before and after the conditioning period to determine the velocity run by the horse at which the blood lactate concentration reached 4 mmol/L (V4). The horses remained at each speed for 5 min. At the end of each speed of the incremental effort stage, the treadmill was turned off for 1 min for blood sample collection. After obtaining the lactate–velocity curve, it was possible to determine the velocity at which the blood lactate concentration reached 2 mmol/L (V2).

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  Figure 3. Schematic representation of the conditioning program performed on the treadmill. The intensity of the conditioning program was established based on V2 (velocity at which the plasma lactate concentration reached 2 mmol/L during the incremental exercise test). The conditioning intensity was increased every three sessions. Each session consisted of the following stages: warm-up, training, and cool-down. The training speeds were individualized, and to avoid repetitive strain injury, they were interspersed with 2 min of speed reduction or increase up to the sixth session. From the seventh session onwards, the horses cantered at the training speed, interspersed with 2 min of speed reduction to trot.

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  Figure 4. Mean ± standard deviation of V4 and V2 obtained in the incremental exercise test (IET). The graph represents the velocities reached in the test before and after the conditioning program. * Significant increase after conditioning compared to before conditioning (p < 0.05).

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  Figure 5. Heat map showing the correlation matrix between echocardiographic and body measurements. The color gradient indicates the correlation between BW, body weight; TC, thoracic circumference; and HR heart rate during echocardiography and other variables obtained and calculated from B-mode, M-mode, mitral flow Doppler (Emax, Amax, Emax:Amax), aortic flow Doppler (PEP, ET, PEP/ET) and tissue Doppler imaging of LVFW (IVRT, Em, Am). Refer to Table 2 and Table 3 for abbreviations.

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  Figure 6. Percentage variation of principal components. The first seven components explained 84% of the variability of the echocardiographic variables. As can be observed, the degree of explainability was low from component eight onwards, justifying the presentation of only ten components.

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  Figure 7. Principal components. In the two-dimensional image, it is possible to visualize the weight of each echocardiographic variable within each component. The variables selected for analysis were: HR, heart rate during echocardiography, and other variables obtained and determined in B- and M-modes with mitral flow Doppler (Emax, Amax, Emax:Amax), aortic flow Doppler (PEP, ET, PEP/ET), and tissue Doppler imaging of LVFW (IVRT, Em, Am). See legends in Table 2 and Table 3.