Jaw Swelling in Horses: Strangles or Grass Mumps?

Finding unusual swellings in the neck or throat area of a horse often causes an immediate sense of dread and stress in horse owners, as the thought of strangles flit through their minds. As hard as it may be, the most important thing to do is take a deep breath and a closer look.

“There are many causes of distinct, focal swellings in the head and neck of horses that aren’t caused by strangles,” reminded Kathleen Crandell, Ph.D., an equine nutritionist for Kentucky Equine Research.

In lieu of strangles—a highly contagious disease of horses that causes abscesses of the lymph nodes, especially the submandibular lymph nodes under the lower jawbone near the neck—consider “grass glands” or “grass mumps” as a potential cause.

Although poorly described in the veterinary literature, this is a common condition reported by owners after their horses have been turned out on pasture. Affected horses present with swelling behind the cheek and beneath the ear, in the area of the throatlatch. The swellings are typically unpainful, incidental findings that appear to have little impact on the horse’s demeanor.

“Unlike strangles, grass glands or grass mumps most commonly are due to a swelling of the parotid gland, not the submandibular lymph nodes,” noted Crandell.

The condition is widely believed to be an allergic reaction; however, the cause remains elusive. Theories include exposure to new, spring grass or sugar-rich grass or pollens. Without a clear understanding of the condition, no specific treatment currently exists.

Other causes of facial swellings in horses include:

• Inflammation of the salivary glands, such as the parotid gland (parotiditis);
• Formation of a stone in the salivary gland or associated duct (sialolithiaisis);
• Trauma;
• Infection (sialoadenitis);
• Neoplasia; and
• Edema (accumulation of fluid) due to prolonged or excessive grazing.

When in doubt, call your veterinarian to have your horse examined. In the meantime, isolate your horse from others until strangles has been ruled out. Remember, not all horses with strangles develop a fever, nasal discharge, or appear otherwise unwell*.

*Duffee, L.R., D.Stefanovski, R.C. Boston, et al. 2015. Predictor variables for and complications associated with Streptococcus equi subsp equi infection in horses. Journal of the American Veterinary Medical Association. 247:1161-1168.