A new study out of Canada shows that uncontrolled respiratory disease in horses may put them at risk for pulmonary artery changes that lead to heart failure.
People with severe asthma can have thickening of the pulmonary arteries, which leads to pulmonary hypertension. Severe equine asthma, like asthma in humans, presents as airway inflammation, coughing and labored breathing; therefore it's feasible that equine asthma can also lead to pulmonary artery thickening, reports EQUUS magazine.
Often called “heaves,” this condition is triggered by mold or dust in hay or the environment. The affected horse must be managed so exposure to these environmental triggers is minimized. Best management practices for horses with heaves include as much turnout as possible, removing horses from stalls when they are cleaned and rebedded, and soaking hay.
Dr. Serena Ceriotti and other researchers at the University of Montreal looked at multiple post-mortem lung samples from 18 horses — six that were in heaves episodes when they died; six with heaves that was in remission because of management practices; and six with no history of heaves.
The scientists measured arterial thickness and found that the horses experiencing active heaves episodes had thicker arteries than the other horses.
Though it's unclear why the arteries thicken, experiments in rodents suggest the low oxygen content and inflammation may increase smooth muscle in the arterial wall. This increase in the muscle decreases the area for blood to flow and may increase muscle contractions, which leads to pulmonary hypertension, minimizing blood flow and limiting cardiac function. This condition can eventually lead to the enlargement and failure of the right ventricle of the heart.
A second portion of the study tested two potential pulmonary hypertension treatments on live horses. One involved reducing the horse's exposure to dust for an entire year and on using hay alternatives. The second used the medication fluticasone for six months then added in dust-control strategies for an additional six months.
The researchers found that both treatments lead to a reversal in artery wall thickness, but this could only be seen once the dust control measurements were enacted. The team notes that hay is the main trigger for heaves; often just changing the horse's diet to include a forage alternative is enough to control the disease.
They conclude that arterial wall remodeling is reversible, but only with strict dust control measures. Inhaled corticosteroids can rapidly improve a horse in experiencing a heaves flareup, but an improved environment is the only way to manage the condition long term.
Read more at EQUUS magazine.
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