Horse Illustrated Magazine

Q:

My horse has the lumps on her back, the vet said they were protein bumps, what causes them, and how do I get rid of them?

A:

What you are describing are likely collagen deposits under your horse’s skin, which are sometimes colloquially referred to as “protein bumps”. Collagen is a protein building block of connective tissue in the body. Although the exact cause of these lumps is unknown, they are thought to be a result of an allergic skin reaction, usually from insect bites. They have also been observed to occur in a location of previous trauma. These lumps have not been shown to have a breed, sex, or age predisposition, but do tend to appear more commonly in the summer months, hence supporting the theory that they are closely involved with an insect allergy. These lumps also go by the longer name of eosinophilic or nodular collagenolytic granulomas.

These lumps are usually not painful and while starting soft, quickly become firm. They can be found singly or in multiples and vary from small to moderate in size. These lumps most commonly are found along the neck, withers, and down the back of the horse, although they can be anywhere on the body.

Treating Protein Bumps

Usually, a single lump does not cause the horse any problems and can be left untreated. However, some owners elect to treat if the lump is large or if there are many of them.

A common treatment involves injecting the lump(s) with a steroid such as triamcinolone or methylprednisolone. This usually results in the resolution of the lump over the course of a few days to a week. An oral course of the steroid prednisolone can also be started if there are too many lumps to make direct injection practical. However, resolution during one season does not mean the horse is free for life. Often, this is a seasonal issue and will reoccur the following year. If this is the case, further investigation into the exact cause of the suspected allergy may be warranted, such as with an intradermal skin test.

Diet and Allergies

There is advice directing horse owners to decrease the amount of protein in the horse’s diet to prevent or cure these lumps, although there is no evidence to support that this is effective in the case of these collagen deposits unless they are the result of a food allergy to a specific protein in the horse’s diet. If a food allergy is the cause, identification and then complete omission of the offending protein would be the only way such a diet modification would help. Attempting to determine what your horse is potentially allergic to is more likely to be helpful.

Managing Insects

Assuming your horse is reacting to insect bites is the best place to start. Re-assessing your barn’s fly control management may yield some ways you can make changes to help reduce the occurrence of these lumps in the future. Installing a fan in your horse’s stall, using a fly sheet, frequently applying a pyrethrin-based fly spray, and stalling your horse during dawn and dusk in a relatively clean stall may help reduce exposure to biting insects.

Other Causes

Additionally, consider if these lumps are a response to irritation caused by tack, especially if the bumps are in a location where either a sheet or blanket is rubbing, or a saddle, saddle pad, or girth has direct contact with the skin.

Hives are another cause for skin lumps and are sometimes called “heat bumps” and occasionally “protein bumps” as well, demonstrating the problem with commonly used, non-descriptive colloquial terms. Hives have a different appearance to collagen deposits; they are flatter and wider, sometimes inches across and can give the skin a wrinkled appearance.

Hives are a much more immediate skin reaction to an allergen and causes for hives is a long list: insects, contact dermatitis, drug reactions, vaccines, certain soaps, plants, feedstuffs, and even stress can cause hives and horses known for sensitive skin can often get hives frequently, just like certain people have more reactive skin than others. As with collagen deposits, the best way to prevent these skin issues in the future is to identify their cause. This can sometimes be challenging and require some detective work. Collaboration with your veterinarian may help.