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Summer Sores

Strategies for Healing Them


Gail M. Staines, Ph.D.

Founder, The Senior Horse

It has been just over a month since my 25-year old Frankie passed away. I am very fortunate to have good friends and family that have been very supportive. It has been challenging. My schedule was intertwined with him and without that I feel like I have been a bit at sea.

Just this week I was provided the opportunity to ½ lease an 18-year old Warmblood gelding. Griffin is a wonderful schoolmaster who I hope will teach me some upper level dressage movements. Unfortunately, he has some allergies, including one that makes him susceptible to summer sores.

I have never had a horse with summer sores, so I decided to do some research.

Here is what I found:

It’s Complicated

Summer sores are known by several names including granular dermatitis and jack sores. The scientific name is habronemiasis. A sore, wound, or areas where moisture accumulates on the horse are perfect places for flies (house, face, and stable) to deposit stomach worm larvae. It is the larvae that causes intense itching and inflammation. (Lenz, n.d.)

But how do flies get the worm larvae in the first place?

They get it from manure, old feed, and dirty bedding.

How does the larvae get into the manure, old feed, and dirty bedding?

Horses eat the larvae that then travels through the digestive system. It takes approximately 2

months for the larvae to mature into adult worms that lay eggs. The eggs travel in the manure where

the flies eat larvae again….and the cycle continues.

Places Summer Sores Like Most

You will commonly see summer sores emerge in the following areas on a horse:

  • Pasterns and fetlocks

  • Around the eyes

  • Ears

  • Corners of the mouth and lips

  • Abdomen

  • Penis and sheath

And, any place that is warm and moist. Injuries such as scratches, cuts, and scrapes that have broken the skin are prime locations for summer sores to develop. (Marcella, 2012)

Getting Rid of Summer Sores

It’s hard! Even if you significantly reduce the summer sores, they can re-emerge in the springtime, after a warmer than normal winter. You will know when your horse begins itching the same areas again.

However, there are some steps that you can take to effectively address summer sores:

Your horse’s environment:

1.) Manure and fly control are a must! This includes cleaning stalls, corrals, pastures, etc. on a daily basis; moving manure as far away from the horses as possible (i.e., spread on pasture horses do not use, have hauled away, a manure pile at the edge of the property, creating a compost pile).

2.) Removal of moist feed.

3.) Keeping horse-areas dry – no standing water, good drainage so you do not have mud.

4.) Keeping your horse dry, especially in those areas prone to summer sore development.

5.) Use of fly traps and insect repellents. (Cudmore, 2020)

Your horse:

1.) Effective de-worming! Before de-worming your horse, have your veterinarian do a fecal egg count (FEC) to determine the type and amount of larvae in your horse’s system. Upon veterinarian’s recommendation, de-worm with products containing ivermectin or moxidectin.

2.) Attending to the summer sores on a daily basis! Wash with an anti-septic skin cleanser such as Betadine. Leave on for 10 minutes before washing off. Dry off area. Apply fly repellant on the summer sore. I am finding that Farnam’s Swat works very well.

3.) Use fly repellant clothing: Fly bonnets, fly sheets with or without a fly hood, and fly leggings are all helpful. Research has discovered that Zebra-patterned fly repellant clothing works best. (Caro, et al., 2019)

If your horse’s summer sores continue not to heal and/or become worse, contact your veterinarian immediately. Your veterinarian may be able to prescribe an anti-inflammatory medication to help with healing. If the summer sores become infected, an antibiotic is in order.

As Pascoe (2020) notes, summer sores are not a one-horse problem. It is a herd issue. As a result, all horses should have a fecal egg count and be de-wormed and treated accordingly.


Caro, T., et al. (2019). Benefits of zebra stripes: Behaviour of tabanid flies around zebras and horses, PLOS ONE.

Cudmore, L. (2020). Cutaneous Habronemiasis or ‘Summer Sores,’ Scone Equine Hospital.

Lenz, T. (n.d.) Summer sores. AAEP.

Marcella, K. (2012). The re-emergence of equine summer sores. DVM360.

Pascoe, E. (2020). How to Treat and Prevent Summer Sores in Horses, Practical Horseman Magazine.


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