Association of submaximal exercise test variables with diagnosis of asthma in a mixed-breed cohort of leisure horses.

Overview

• This study examined whether a submaximal exercise test (SET) could effectively diagnose and stage asthma in leisure horses of mixed breeds.
• Researchers measured various clinical and laboratory parameters during and after exercise but found limited ability to distinguish between healthy and asthmatic horses using these tests.

Background and Objective

• Submaximal exercise tests (SETs) are commonly used to assess respiratory health in different species, including horses.
• Asthma in horses varies from mild to severe and can be challenging to diagnose, especially in field conditions.
• The study aimed to determine if SETs could help identify and stage asthma severity in leisure horses of mixed breeds based on clinical and laboratory data collected at specific exercise intervals.

Methods

• Animals: 26 privately owned leisure horses with mixed breed backgrounds.
• Groups: Horses were classified into four groups based on clinical history, examination, and bronchoalveolar lavage fluid (BALF) cytology:
  • Healthy (8 horses)
  • Mild asthma (miEA) (4 horses)
  • Moderate asthma (modEA) (7 horses)
  • Severe asthma (sEA) (7 horses)
• Study design: Cross-sectional clinical study using hospital cohort data.
• Exercise test protocol:
  • SET on a lunge track including ECG, arterial blood gases, lactate, respiratory rate (RR), and heart rate (HR) monitoring.
  • Samples were collected at multiple time points:
    • Rest (T0)
    • After two intervals of 2-minute trot (T1, T2)
    • After two intervals of gallop (T3, T4)
    • Followed by 3-minute trot (T5) and gallop (T6)
  • Measurement of heart rate and respiratory rate recovery times after exercise.
• Data analysis:
  • Ordinal models evaluated predictive value of SET variables for asthma diagnosis.
  • Statistical tests included Kendall’s tau for correlation and likelihood ratio tests (LRT) for significance.

Key Findings

• Oxygen partial pressure (pO2) at rest (T0):
  • Showed the strongest negative association with asthma diagnosis (τ = -0.513, highly significant).
  • Lower resting pO2 predicted more severe asthma cases.
• Oxygen levels at end of exercise (T6):
  • All healthy and mild asthma horses had lowered oxygen partial pressure indicating hypoxemia at this point.
  • Some moderate and severe asthma cases had increased pO2 at T6 compared to T0, which was an unexpected finding.
• Recovery times for RR and HR:
  • Did not significantly correlate with asthma diagnosis (RR adj. P=0.493, HR adj. P=0.287).
  • There was considerable variation within groups, making these measures unreliable for diagnosis.
• Other SET measured variables:
  • Lactate levels and ECG findings did not show diagnostic value for asthma staging in this cohort.

Conclusions

• The standardized submaximal exercise test did not provide clear benefit in diagnosing or staging asthma in leisure horses.
• The overlap of SET parameters between healthy and asthmatic horses suggests limited utility for field diagnosis based on this method.
• Resting arterial oxygen partial pressure was the most reliable predictor of severe asthma but was not sufficient alone for diagnosis or staging.
• The study highlights the challenges in diagnosing mild asthma in horses and suggests that SETs may not be the most effective diagnostic tool in such cases.
• Further research may be needed to identify more sensitive or specific diagnostic methods for equine asthma in mixed-breed leisure horses.

Implications for Veterinary Practice

• Veterinarians should be cautious about relying solely on submaximal exercise tests to diagnose asthma in horses.
• Diagnostic protocols may need to incorporate comprehensive clinical evaluation, BALF cytology, and resting blood gas measurements rather than exercise testing alone.
• Exercise tests might still have value in broader respiratory assessments but are insufficient for clear differentiation of asthma status or severity.