As winter approaches, horses spend more time stabled and eat more hay, which can increase their exposure to dust, mould spores and other airborne irritants. This article explains how the horse’s lungs protect themselves, and why repeated exposure can lead to inflammation even when there’s no obvious cough. We compare haylage, soaked hay and steamed hay, including the pros and cons of each. We also look at the bedding, ventilation and stable management changes that make a difference, and when it’s time to call the vet.