OzVet

A horse cannot breathe through it’s mouth, it can only breathe through it’s nose. So, that’s why you don’t ever see a horse panting or breathing hard through it’s mouth after a hard workout.

Also, horses can’t throw up (which is why they end up with colic and bloat and all sorts of other wonderful digestive problems). There’s a nice little band of muscle around the esophagus as it enters the stomach that forms a one-way valve. This prevents anything from coming back up. (Humans have a similar valve, but it’s a lot weaker, meaning we can throw up. Also, the angle between the stomach and esophagus makes it easier for us to vomit and much harder for a horse.)