Horses can swallow large portions of hay not properly chewed first. The bolus of hay can then become lodged in the esophagus. Some horses are predisposed to choke. Since many older horses can't chew food into small pieces and might end up swallowing it whole, modifying the diet to include softened feeds such as dampened pellets rather than feeding hay and long grasses could help prevent choke. Owners should not feed hay cubes or large, fibrous horse treats to horses that are not used to them because this might predispose them to choke.
Size can be a predisposing factor.
Horses often ingest bedding, such as wheat straw or wood shavings, and a miniature horse or foal can easily choke on it because of a small esophagus. To prevent choke, you might have to remove bedding or use a muzzle. Some older horses with no teeth will benefit from special muzzles, like grazing muzzles, so they can't eat big chunks of food. These muzzles can be found at tack shops or in tack catalogues. When horses eat, they chew food until it forms a bolus, then push the bolus into the back of the pharynx and swallow it.