Respiratory disease is common in horses kept in stables and ranges from mild cough to severe heaves requiring medical management and environmental change.
Equine asthma in its severe form causes significant and ongoing suffering through labored breathing that makes even rest uncomfortable. The heave line, a characteristic groove in the flank from constant use of abdominal muscles to force air from stiff lungs, represents evidence of sustained respiratory effort that would be exhausting in humans. Subclinical respiratory inflammation, while not obviously distressing, reduces oxygen delivery and exercise capacity, limiting horses ability to express natural movement behaviors. Most equine asthma is caused by the environment humans create for horses: dusty stables, dry hay, and poor ventilation. Recognizing that respiratory disease in horses is primarily a management failure rather than an inevitable occurrence reframes welfare responsibility clearly onto human decisions.