Field-training in young two-year-old thoroughbreds: investigating cardiorespiratory adaptations and the presence of exercise induced pulmonary hemorrhage

Shannon Massie; Warwick Bayly; Hajime Ohmura; Yuji Takahashi; Kazutaka Mukai; Renaud Léguillette

doi:10.1186/s12917-024-03997-x

Field-training in young two-year-old thoroughbreds: investigating cardiorespiratory adaptations and the presence of exercise induced pulmonary hemorrhage

BMC Vet Res. 2024 Apr 26;20(1):159. doi: 10.1186/s12917-024-03997-x.

Authors

Shannon Massie¹, Warwick Bayly², Hajime Ohmura³, Yuji Takahashi³, Kazutaka Mukai³, Renaud Léguillette⁴

Affiliations

¹ Faculty of Veterinary Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, T2N 4Z6, Canada.
² College of Veterinary Medicine, Washington State University, Grimes Way, Pullman, WA, 99164, USA.
³ Equine Research Institute, Japan Racing Association, 1400-4, Shiba, Shimotsuke-shi, Tochigi, 329-0412, Japan.
⁴ Faculty of Veterinary Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, T2N 4Z6, Canada. rleguill@ucalgary.ca.

Abstract

Background: Comparatively little is known regarding the initial cardiorespiratory response of young racehorses to training. The objectives were to compare physiological parameters before and after introductory training and determine whether young Thoroughbreds show endoscopic signs of exercise-induced pulmonary hemorrhage (EIPH). Ten Thoroughbreds (20-23 months) underwent 12-weeks of introductory training, including weekly speed sessions. Two 600 m high-speed exercise tests (HSET) were performed following weeks 4 and 12 while wearing a validated ergospirometry facemask. Peak oxygen consumption (V̇O₂pk) and ventilatory parameters (tidal volume, V_T; peak inspiratory and expiratory flow, PkV̇_I, PkV̇_E; respiratory frequency, Rf; minute ventilation, V̇E) were measured. The ventilatory equivalent of oxygen (V̇E/V̇O₂) and the aerobic and anaerobic contributions to energy production were calculated. Maximal heart rate (HR_max) and HR at maximal speed (HR_Vmax) were determined. Post-exercise hematocrit, plasma ammonia and blood lactate were measured. Evidence of EIPH was investigated via tracheobronchoscopy post-exercise. Results were compared (paired t-test, P < 0.05).

Results: Horses were faster following training (P < 0.001) and V̇O₂pk increased 28 ml/(kg total mass.min) (28 ± 16%; P < 0.001). Ventilatory (V̇E, P = 0.0015; Rf, P < 0.001; PkV̇_I, P < 0.001; PkV̇_E, P < 0.001) and cardiovascular parameters (HR_max, P = 0.03; HR_Vmax, P = 0.04) increased. The increase in V̇E was due to greater Rf, but not V_T. V̇E/V̇O₂ was lower (26 ± 3.6 vs 23 ± 3.7; P = 0.02), indicating improved ventilatory efficiency. Anaerobic contribution to total energy production increased from 15.6 ± 6.1% to 18.5 ± 6.3% (P = 0.02). Post-exercise hematocrit (P < 0.001), plasma ammonia (P = 0.03) and blood lactate (P = 0.001) increased following training. Horses showed no signs of EIPH.

Conclusions: Young two-year-old Thoroughbreds responded well to introductory training without developing tracheobronchoscopic evidence of EIPH.

Keywords: EIPH; Heart rate; Lactate; Ventilation.

MeSH terms

Adaptation, Physiological
Animals
Female
Heart Rate
Hemorrhage* / veterinary
Horse Diseases / physiopathology
Horses
Lung Diseases / veterinary
Male
Oxygen Consumption*
Physical Conditioning, Animal*