A horse can react strongly to an environmental allergen on a skin test without having asthma, according to new research that also explored the role of air quality in equine respiratory disease.
The study, published in the Journal of Equine Veterinary Science, examined 52 horses at four locations in Texas. All had signs or a history consistent with asthma. Researchers analysed fluid collected from the horses’ airways to assess inflammation, tested blood samples for inflammatory markers and measured airborne particles where the horses were kept. A smaller group of 31 horses also underwent intradermal skin testing for common environmental allergens.
Airway fluid results supported an asthma diagnosis in 34 of the 52 horses. Yet skin test reactions did not reliably distinguish the different types of airway inflammation. Among horses that received a skin test, every horse without an asthma diagnosis reacted severely to at least one allergen, compared with 60% of those diagnosed with asthma.
The researchers also found no blood inflammatory marker in their panel that reliably identified a particular asthma type.
What did air quality show?
The study found a higher than expected proportion of horses with mast cell related airway inflammation at sites where the measured air quality was rated unhealthy. Horses with neutrophil related inflammation were found only at sites with unhealthy air quality.
These findings add to interest in the relationship between the air horses breathe and their respiratory health. However, the study involved only four locations, with different numbers of horses at each. The air quality results show an association; they cannot establish that the measured conditions caused asthma in these horses.
The findings suggest that a positive skin allergy test alone may give an incomplete picture when investigating a horse’s respiratory signs. The researchers emphasise the value of assessing inflammation in the airways and the horse’s environment when trying to understand what may be contributing to its condition.
