Horse With Swollen Lumps On Neck - Grass Glands or Mumps

Horse owners from Massachusetts, to Connecticut and Alabama have discovered the same thing: their horse goes out into the pasture and comes back in with lumps from egg size to small water balloons on the crease of their neck. They almost instantly worry and wonder whether this could be an infection, perhaps strangles, or a thyroid gland condition, or tumor, however eventually the lumps go away all by themselves and everybody wonders what just happened.

Here are some photos taken by other horse owners from different locations. We don't claim ownership of these photos, but post them to show examples of what grass glands, or grass mumps looks like for educational purposes to help other horse owners who are just as stumped as we were when first confronted with these mysterious lumps. Many said it happened mostly in fall, but no one really doesn't know exactly why predominantly in fall.

Horse owners who have been through this "episode of strange lumps" on their horse's neck a few times in a row agree, that rather than something malignant, or a bad thyroid gland, or infection it seems to be "just" an allergic reaction to something in the pasture; some suspect perhaps an adverse reaction* to pig weed (*unconfirmed). Some common allergens that might affect our horses include molds and pollen from cocklebur and ragweed.

The Horse and Hound website referenced below provided us with more answers:

Quote: "Affected horses can look rather like hamsters and may be reluctant to work with their head down on the bit. Such lumps are commonly mistaken for a manifestation of the disease strangles, when in fact they are simply swellings of the parotid salivary glands. Such swollen glands can vary in size from day to day. They are often linked with particular areas of grazing and are suspected to be a form of allergic reaction."

It is often difficult to figure out exactly what triggered your horse's allergic reaction. Often, a plant in bloom or pollen in the air can cause a slight allergic reaction in a horse.

Here is the article on Grass Glands from Horse and Hound:

http://www.horseandhound.co.uk/horsecare/1370/105253.html 

This is the classic example that will worry many people more than it does their horse. Everyone will have seen it at some time, yet it is poorly understood. Frequently, a horse or pony will be brought in from the field after grazing for some hours with large, firm and usually painless swellings behind the jawbone at the back of the throat, beneath where the throat lash would go. Occasionally, the swelling will be accompanied by some fluid swelling under the skin. 

The glands enlarge after the horse has been out at grass and most return to normal size within 36hr of coming in with no treatment. It helps if such horses, when affected, are fed from a height once they are brought in, to allow any accumulation of fluid to drain down...

------------- For reference:

Horse Salivary Glands and Location of Thyroid

What at first glance resembled a tumor, swollen thyroid gland, or an infected salivary gland on our horse's throat indeed completely disappeared within less than 48 hours.

Our initial research led to more clues and answers on grass glands and exposure to plants, pollen, mold and dust in the pasture, which can cause a horse to experience an allergic reaction, including a swollen area in the jaw line. The good part is, that next time the horse returns from the pasture with these lumps we will worry less. We know now that there is no need to do anything except carefully examine the area to confirm it is just a swollen parotid gland.

Here is an illustration found on the Internet showing the location of the horse's salivary glands (for those who worry about possible strangles) and the location of the thyroid (for those who worry about a possible thyroid condition). The small photo, again, borrowed from the Internet as reference shows a foal's neck with a swollen thyroid gland (goiter).

Of course, if your horse looks ill or the swelling persists for more than 36-48 hours, call your vet.

Here is the Equus Medication Basics Chart for your horse.