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Some horses with heaves may benefit from antimicrobial medications in addition to conventional treatment, according to a new Canadian study.
Researchers at the University of Saskatchewan examined 11 horses with a history of severe equine asthma, a narrowing of the small airways of the lungs commonly referred to as heaves. Along with the classic clinical signs of the condition---including labored breathing and flaring nostrils---the horses were found to have bacteria in their airways and elevated levels of white blood cells in their lungs, which is a sign of inflammation.
The correlation between heaves and airway bacteria isn’t well understood but may be significant, says Julia Montgomery, Med Vet, PhD, DACVIM (LAIM). “With everything we are learning about the microbiome, including new diagnostic non-culturebased methodologies to detect bacteria, we are moving away from the old assumption that the lower airway is ‘sterile,’” she says. “It is now generally accepted that all airways, including healthy ones, harbor some bacteria. In people, the presence of certain types of bacteria is associated with
asthma exacerbations and other chronic lower airway diseases. Since severe equine asthma is characterized by neutrophilic inflammation, and neutrophils tend to be recruited in bacterial infections, we were interested to study if a similar relationship exists in horses.”
All of the study horses received conventional heaves care: Measures were taken to reduce dust and other airborne irritants in their environment, and they were given corticosteroids to combat inflammation and bronchodilators to open their airway passages.
Six of the horses were also given two doses of longacting ceftiofur, a broadspectrum antibiotic commonly used to treat equine airway infections. The remaining five horses were given saline placebo treatment. At the end of the 16-day study period, the horses were once again examined for clinical signs of heaves and tested for airway inflammation and bacteria.
The data showed that the horses treated with the antimicrobial showed a significant reduction in clinical signs of asthma by the end of the study, along with a decrease in certain neutrophil activity in their lungs. Other measures of airway inflammation remained unchanged between the treated and placebo groups.
While these results are encouraging, Montgomery is quick to point out antimicrobial medications are appropriate only for certain heaves cases.
“This study only looked at horses who also had a positive tracheal wash bacterial culture, so based on our results the decision will still have to be made for any individual horse based on the diagnostic test results and at the discretion of the treating veterinarian,” she says. “There may be a subgroup of horses that may benefit from the addition of antibiotics because they have a bacterial component to their airway problem, but this should not be generally applied to every horse with asthma. On the contrary, the use of antimicrobials should be clearly indicated before adding them to the horse’s treatment plan.”
Reference: “Does antimicrobial therapy improve outcomes in horses with severe equine asthma and a positive tracheal wash bacterial culture?” The Canadian Journal of Veterinary Research, July 2018
Hands-on examination that includes putting pressure directly on the horse’s back continues to be the most common diagnostic technique.