Inspiratory muscle training for the treatment of dynamic upper airway collapse in racehorses: A preliminary investigation

Effects of a 15° Variation in Poll Flexion during Riding on the Respiratory Systems and Behaviour of High-Level Dressage and Show-Jumping Horses

From previous studies, the International Society for Equitation Science has advised that further research be conducted on the physiological/psychological effects of less-exacerbated poll flexion angles. We aimed to evaluate the effects of two riding poll flexion positions with a difference of only 15° on the respiratory systems and behaviour of horses through an evaluation of dynamic airway collapse via over-ground endoscopy, the pharyngeal diameter, pleural pressure, arterial oxygenation and lactate, HR/RR, and the occurrence of conflict behaviours. Twenty high-level dressage and twenty show-jumping horses underwent a 40 min ridden test at a ground angle of 85°; 3 weeks later, they underwent a ridden test at a 100° ground angle (the angle between the ground and the line from the forehead to the muzzle) and in a cross-over design. Using a mixed model for repeated measures, Wilcoxon/Friedman tests were carried out according to the experimental design and/or error normality. For both groups, at 100°, conflict behaviours and upper airway tract abnormalities were significantly more frequent, and the pleural pressure was higher, and the pharyngeal diameter was lower. At 85°, relaxation behaviours were significantly more frequent. Lactate was significantly higher at 100° only in the dressage horses. Compared to the first test at 85°, the HR/RR were significantly lower at the beginning of the second test (at 100°) but higher at the end. The significant differences identified in these dressage and show-jumping horses support the idea that an increase of just 15° in riding poll flexion can have negative effects on the respiratory system and behaviour of a horse and therefore on its welfare.

Training the equine respiratory muscles: Ultrasonographic measurement of muscle size

BACKGROUND

Limited information exists regarding changes in the size of respiratory and locomotor muscles in response to exercise training in the Thoroughbred racehorse.

OBJECTIVES

To describe and compare the responses of the respiratory and locomotor muscles to conventional exercise training and inspiratory muscle training (IMT).

STUDY DESIGN

Prospective randomised controlled trial.

METHODS

Thoroughbred racehorses, in training for competition in National Hunt races, were recruited from two training establishments. Ultrasonographic images were obtained for selected muscles of the upper airway, diaphragm, accessory respiratory, and locomotor systems and their sizes measured. Examinations were performed at three timepoints: (A) when unfit, (B) following 12 weeks of conventional exercise training and (C) following 10-12 weeks continued training at race fitness. In addition, horses at yard 1 performed IMT, between timepoint B and C, and were randomly assigned into high-load (treatment) or low-load (control) group. Repeated measures models were constructed to compare the change in muscle measurements over time, and to investigate the effects of yard, previous airway surgery and IMT on the change in ultrasonographic size measurements obtained.

RESULTS

Upper airway muscle size increased in response to conventional race training between timepoints A-C, and B-C. Diaphragm size increased in response to conventional exercise training between timepoints A and B. The diaphragm size of horses that undertook high-load IMT was either maintained or increased, whereas diaphragm size decreased in horses that undertook low-load IMT or no IMT between timepoints B and C. A significant interaction between gluteal muscle size and airway surgery status was observed, with greater gluteal muscle thicknesses measured in horses that had not previously undergone airway surgery (left gluteal 3.9%, p < 0.001; right 4.5%, p = 0.04).

MAIN LIMITATIONS

Low number of horses underwent IMT.

CONCLUSIONS

Respiratory and locomotor muscles increase in size in response to conventional exercise training, with a further change in diaphragm size in response to inspiratory muscle training.

Training the equine respiratory muscles: Inspiratory muscle strength

BACKGROUND

Little is known about the response of the equine respiratory muscles to training.

OBJECTIVES

To measure an index of inspiratory muscle strength (IMSi) before and after a period of conventional exercise training (phase 1) and inspiratory muscle training (IMT), comparing high-load (treatment) and low-load (control) groups (phase 2).

STUDY DESIGN

Prospective randomised controlled trial.

METHODS

Phase 1: Twenty National Hunt Thoroughbred racehorses performed an inspiratory muscle strength test (IMST) twice on two occasions; when unfit at timepoint A (July), and when race fit at timepoint B (October). Phase 2: Thirty-five Thoroughbred racehorses at race fitness were randomly assigned into a high-load (treatment, n = 20) or low-load (control, n = 15) IMT group. The high-load group followed an IMT protocol that gradually increased the inspiratory pressure applied every 4 days. The low-load group underwent sham IMT with a low training load. The IMT was performed 5 days/week for 10 weeks. The IMST was performed twice on two occasions, timepoint B (October) and timepoint C (January). Conventional exercise training and racing continued during the study period. The peak IMSi values obtained from the different groups at timepoints A, B and C were compared using a Wilcoxon Signed Rank Test.

RESULTS

Phase 1: There was a significant increase in IMSi from timepoint A: 22.5 cmH₂ O (21-25) to timepoint B: 26 cmH₂ O (24-30) (p = 0.015). Phase 2: From timepoint B to C there was a significant increase in IMSi for the high-load group 34 cmH₂ O (28-36) (p = 0.001) but not the low-load group 26 cmH₂ O (24-30) (p = 0.929). The peak IMSi at timepoint C was significantly higher for the high-load than low-load group (p = 0.019).

MAIN LIMITATIONS

Single centre study with only National Hunt horses undergoing race-training included.

CONCLUSIONS

In horses undergoing race training there is a significant increase in IMSi in response to conventional exercise training and high-load IMT.

Association between dynamic upper airway obstructions and fitness parameters in Standardbred racehorses during high-speed treadmill exercise

OBJECTIVE

To evaluate the association between the severity of dynamic upper airway obstruction (DUAO) and selected fitness parameters in Standardbred racehorses measured by treadmill test.

ANIMALS

191 Standardbred racehorses that underwent a standardized diagnostic protocol for poor performance evaluation between 2002 and 2021 at the Veterinary Teaching Hospital, University of Milan.

PROCEDURES

Horses underwent a diagnostic protocol including clinical examination, lameness evaluation, laboratory analyses, ECG, resting upper airway endoscopy, metabolic incremental treadmill test, high-speed treadmill endoscopy, postexercise tracheobronchoscopy, and bronchoalveolar lavage fluid cytology. On the basis of findings of the high-speed treadmill endoscopy, horses were divided into the following groups: no DUAO, mild DUAO (medial deviation of the aryepiglottic folds or epiglottic entrapment), severe DUAO (dorsal displacement of the soft palate, nasopharyngeal collapse, dynamic laryngeal collapse, or epiglottic retroversion), and multiple DUAOs (different forms of DUAO occurring concomitantly). Fitness parameters, measured by incremental treadmill test, included speed at a heart rate of 200 bpm (V200), speed and heart rate at a lactate concentration of 4 mmol/L (VLa4, HRLa4), peak lactate, maximum speed, maximum hematocrit, and minimum pH. Data were compared between groups by use of descriptive and statistical analyses.

RESULTS

Horses affected by severe or multiple DUAOs showed lower V200 and VLa4, compared to the no-DUAO group; horses with multiple DUAOs also had higher peak lactate concentrations compared to horses without DUAOs.

CLINICAL RELEVANCE

While mild forms of DUAO do not affect athletic capacity, severe forms of DUAO and multiple DUAOs may lead to reduced fitness in Standardbred racehorses by impairing aerobic capacity.