Question of the Week: Sensitivity to Gnats

Q: My horse has always had sensitive skin, but this year the gnats seem to have really taken a toll on him. He has rubbed some of the hair off of his chest, neck and face, and he’s started rubbing his mane and tail. He spends much of the day walking circles around his paddock trying to get away from the bugs. I’ve tried using fly spray, but it doesn’t seem to work for him. What can I do to help him?

A: As the warmer weather draws near, so do the insects. Like people, some horses are much more sensitive to insect bites than others. Your horse seems particularly sensitive and the gnats you mention are Culicoides species. Culicoides hypersensitivity in horses is extremely common and is very much like flea allergy dermatitis in dogs. Interestingly, a study done in 1992 showed that in certain horses, skin sensitivity due to insect bites can be partially hereditary. Unfortunately there is no real cure for this type of skin condition but there are a few tricks you can use to help manage it and make your horse more comfortable.

First let’s start with environmental adaptations. Changing the time of day you turn out your horse may help. Culicoides feed at dusk and dawn, so avoiding turning your horse out at pasture during those times. When your horse is stalled, install a large fan to create a nice strong breeze in the stall; this will help prevent bites as well. Secondly, take note of the manure situation at your barn. Is the manure piling up in the paddocks and stalls? Is the manure heap near the stable? Proper manure management can help decrease the number of insects to a certain extent. Likewise, Culicoides require standing water to breed, so minimizing small stagnant pools near the barn will also help (as well as decrease the number of mosquitoes, which is always an added bonus).

For dealing with your horse specifically, sometimes if the skin irritation is pronounced enough to cause the excessive rubbing and behavioral changes that you are describing, medical intervention for a brief period of time may be warranted. For starters, a medicated shampoo can help clean and sooth any raw or irritated spots your horse has created by rubbing. Any type of oatmeal-based shampoo is mild and soothing. Shampoos containing an antibacterial cleaning agent such as chlorhexidine may also help if your horse’s coat is looking greasy or some of the affected areas appear slightly infected. Your vet may prescribe medication such as an oral antihistamine for a short period of time to help decrease the itchiness and inflammation in the skin. Depending on how badly affected your horse is, a short course of steroids such as prednisolone may also be prescribed to break this cycle of constant itchiness, which prevents healing.

Blanketing your horse with a flysheet may work too, although some horses have been known to rub right through them if the itch is strong enough.

Lastly, don’t give up on the fly spray. Make sure you are using a spray that contains permethrin, a strong insecticide. Yes, your horse will sweat the spray off in a few hours, so the best use of fly spray is strategic use: apply it when the horse will need it the most (like during dawn and dusk, or in the heat of the day for flies). Don’t be afraid to use fly spray twice daily or after your horse has been sweating a lot, such as after a summer ride.

— Anna O’Brien, DVM

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