Simply put, haylage is partially-fermented hay. Haylage has a higher moisture content usually between 40%-60%, this moist environment creates a drastic reduction in dust found in the feed which is beneficial for horses with respiratory issues.
Haylage is an amazing choice as animal feed because it retains more nutrients and is more palatable than dry hay. The higher moisture content and fermentation process makes haylage easier to digest and enhance the beneficial microbiota in the hindgut.