The horse can not breathe through the mouth. If you close her nostrils, she suffocate Bashny.Net

Nostrils play an important role in the life of the horse. If it is excited or tired from running, they greatly expand, to let in more air. The design of the horse breathing apparatus ensures that it can absorb a large amount of air at a time, which allows it to provide oxygen to the entire body weight over a long non-stop movement.

However, this structure has a significant vulnerability: too long soft palate closes the root of the tongue, which excludes the possibility of mouth breathing. If for some reason will be blocked nostrils, a horse suffocated.

via factroom.ru