Oxygen consumption, locomotory-respiratory coupling and exercise-induced pulmonary hemorrhage in horses during the Paso Fino gait.

Background: Workload associated with the high frequency Colombian Paso Fino gait has not been evaluated.

Objectives: To determine the oxygen consumption (V̇O₂), heart rate (HR), stride frequency: breathing ratio, and hematology associated with the Paso Fino gait, including whether exercise-induced pulmonary hemorrhage (EIPH) occurs.

Animals: Eleven Paso Fino horses.

Methods: Prospective cohort study. Horses performed a standardized Paso Fino gait test across a wooden sounding board, simulating competition. V̇O₂ and ventilatory parameters (tidal volume [V_T]; peak inspiratory and expiratory airflows [PkV̇_I, PkV̇_E]; respiratory rate [RR], minute ventilation [V̇E]) were measured using a portable ergospirometry facemask. Heart rate was measured using electrocardiograms. Post-exercise lactate, hematocrit, bicarbonate, pH, electrolytes, and biochemistry concentrations were measured. EIPH was assessed via tracheobronchoscopy. Four horses completed a secondary high-intensity gallop to elicit peak V̇O₂ for comparative purposes.

Results: Median [IQR] mean individual HR during the Paso Fino gait was 190 [178, 201] bpm. Relative V̇O₂ measured 49.8 [48.4, 59.5] mL/(kg min; V_T = 8.6 [8.0, 10.7] L; RR = 87.1 [75.4, 99.5] bpm; V̇E = 869 [740, 902] L/min; PkV̇_I = 33.4 [32.7, 37.2] L/s; PkV̇_E = 44.2 [40.3, 46.0] L/s). Horses took 2.8 [2.7, 2.9] strides/second and had a stride frequency: breathing ratio of 2.0 [1.8, 2.3]. Post-exercise blood lactate concentration and hematocrit measured 2.7 mmol/L and 50% respectively. Three horses showed endoscopic evidence of Grade-1 EIPH. The Paso Fino gait V̇O₂ and HR equaled 79% V̇O₂pk and 91% maximal HR, respectively, based on the high-intensity gallop.

Conclusions and clinical importance: The Paso Fino gait represents submaximal exercise based on V̇O₂ < V̇O₂pk and blood lactate.