The muzzle is the forward-projecting portion of a horse’s head that encompasses the nostrils, the upper and lower lips, and the underlying premaxillary and mandibular structures. It is one of the named points of the horse used in conformation assessment. The muzzle houses numerous sensory nerve endings and vibrissae (tactile whiskers) that allow the horse to discriminate between feedstuffs and detect objects in low-light conditions; removal of vibrissae for cosmetic purposes is prohibited in some jurisdictions and equestrian disciplines. The nostrils within the muzzle are highly distensible during exercise, expanding to maximize airflow since horses are obligate nasal breathers. Mucous membranes visible at the nostrils and lips provide a rapid assessment point for hydration and circulatory status, as described in the mucous membrane entry. Muzzle conformation varies across breeds: fine, tapered muzzles are characteristic of Thoroughbreds and Arabians, while broader muzzles are common in draft breeds. In veterinary contexts, a grazing muzzle is a perforated basket device fitted over the muzzle to restrict grass intake in horses at risk of laminitis. See also mucous membrane color and moisture as the primary clinical reading taken at the muzzle during physical examination, and laminitis management for why a grazing muzzle is prescribed as a dietary restriction device.
Further Reading: The anatomy of the equine muzzle — nasal structure, vibrissae, and sensory function — is covered in the Muzzle (anatomy) article on Wikipedia. For clinical assessment of mucous membrane color and hydration at this site, see the Utah State University Extension equine health resources.