Question:
Is there anything that can be done to help a horse with extremely sensitive skin? My mare seems to have over-the-top reactions to bug bites and always has at least one patch of mystery skin crusties on her body. Last spring, she lost giant patches of hair around her eyes and ears that didn’t grow back until late fall. My gelding, kept in the same location and generally cared for in the same way, has none of these issues. I keep my mare very clean and I protect her from flies as much as I can, but her skin is always an ongoing problem. What else can I do?
Answer from Rosanna Marsella, DVM, DACVD:
You are seeing the results of insect-bite hypersensitivity (IBH) in your mare. Put simply, she has insect allergies while your gelding does not. This physiological difference means that in the same environment these horses have very different responses to insect exposure. Allergic horses are not only extremely sensitive to the saliva of biting insects but are prone to secondary bacterial infections that manifest with crusting, bumps and hair loss. The face and ears are favorite target sites for Culicoides, the tiny biting flies often called midges, which is why you are seeing hair loss in those areas.
Protecting against insect-bite hypersensitivity (IBH)
The usual fly-control products and measures may not provide sufficient protection for horses with IBH. Moving forward, I suggest you implement a very aggressive fly-spray regimen. For maximum protection, use products containing permethrin or cypermethrin. If your horse is allergic to permethrin, products containing neem oil are a good alternative. Citronella and pyrethrin are not strong repellents.
To be effective, fly sprays need to be used daily and in generous amounts. To repel bugs from the face and ears try applying spot products containing permethrin to the poll area since spraying a horse’s face isn’t easy for you or pleasant for the horse.
Midges are not strong flyers, so setting up fans in areas where your mare spends her time can also help protect her from bites. Fans are particularly important during the evening hours, because midges are most active at sunset. I generally discourage using fly sheets for horses with IBH because the heat and sweat underneath them can promote even worse skin infections.
Dealing with scabs and bald patches
If you notice your mare is developing scabs and bald patches, wash the area with chlorhexidine shampoo once or twice weekly. An antibacterial and antiseptic agent, chlorhexidine is effective against a broad range of bacteria, fungi and viruses. Leave the shampoo on the horse’s skin for 10 minutes before rinsing.
If your mare becomes extremely itchy, you can “spike” her fly spray with a small amount of steroids—talk to your veterinarian about adding a bit of dexamethasone to whatever product you are using. This is a much safer way to provide relief than giving dexamethasone orally or by injection.
Fly control is essential
Hopefully in the future we will have vaccines to help horses like your mare. But, so far published studies have shown that vaccines that use insect extracts to desensitize horses do not work. This means we need to gear up our fly-control efforts and use fans during the hottest months of the year to protect horses like your mare who are very sensitive to insect bites. Management of insect allergic horses is possible, but it requires dedication and lots of repellents.
Rosanna Marsella, DVM, DACVD
University of Florida
Gainesville, Florida
Our expert
Rosanna Marsella, DVM, DACVD, is a board-certified veterinary dermatologist and a professor at the University of Florida College of Veterinary Medicine. She is the author of several books, including the Manual of Equine Dermatology, and more than 150 peer-reviewed articles. She is a past president of the American College of Veterinary Dermatolog