Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose

Parotiditis, Parotid Gland Swelling

Synonyms: Grass Glands, Grass Mumps


The normal parotid salivary glands are large, lumpy-feeling glands that lie right behind the jaw bones, in a vertical line from the base of the ear to the jugular groove.

In grazing horses, these glands may become obviously enlarged, a condition known as parotiditis. This is thought to be an allergic response to an allergen (probably pollens) at pasture.

When horses are taken off pasture, the swelling decreases. Usually, horses with parotiditis are normal otherwise. The swelling of the glands does not seem painful or bothersome. In some cases, the veins of the face may stand out or bulge. This is caused by the swollen parotid glands that press on the jugular and its tributary veins, damming the blood back up into the face.

my vet's role


Prognosis is good and, in many cases, horses can be returned to pasture later without recurrence.

my role

Questions To Ask Your Vet:
  • Can my horse be returned to pasture after they recover?

The only way to prevent parotiditis is to deny horses access to pasture.

Related References:

Schmotzer WB, Hultgren BD, Huber MJ, et al. Chemical involution of the equine parotid salivary gland. Vet Surg 1991;20(2):128-32.

Author: Doug Thal DVM Dipl. ABVP