Biting insects aren?t just a nuisance. They also transmit diseases like encephalitis, Lyme disease and equine infectious anemia.
Screened barns, proper manure disposal, fly sheets and masks, fly traps and predators (more on that in our June issue) are all effective in reducing the insect problem, but You’ll still need an effective fly spray, even if it’s only for riding and farrier/vet work. And, when you need a no-fail solution, your best bet is to go straight to the chemical-based formulas, which we?ve included in this article.
How They Work
There are three basic types of active ingredients in equine fly sprays:
Insecticides.These actually kill insects. Equine fly sprays contain pyrethrins and pyrethroids. These are the ingredients ending in ?ethrin.?
Repellents. Repellents discourage insects, but don’t kill them. Butoxypolypropylene glycol. n-octyl Bicycloheptene Dicarboxamide. Dipropyl isocinchomeronate.
Synergists. These increase the potency of pyrethrins and pyrethroids by inhibiting the enzymes that break them down. Piperonyl butoxide and n-octyl Bicycloheptene Dicarboxamide.
The pyrethrin and pyrethroid insecticides don’t only work at the surface. They?re absorbed through the skin, as are the synergists and repellents. As long as these things are circulating in the blood, the horse will be unappealing to insects. Products with the longest duration of activity contain the synergists, which slow the breakdown of the insecticides.
Pyrethrins and pyrethroids are nervous-system toxins. However, because of their higher body temperature, mammals metabolize them quickly, and it would take extremely large doses across the skin to produce nervous-system signs. You?d likely see skin-sensitivity reactions first.
Although millions of horses use these products with no evidence of toxicity, the fact they?re absorbed shouldn?t be ignored. Be particularly observant in debilitated horses, horses receiving other agents with potential CNS toxicity (like moxidectin) and be sure your veterinarian is aware that you?ve been using them if your horse needs surgery. Use only in a well-ventilated area to minimize respiratory tract irritation to you and your horse, and remember you will absorb it across your skin also.
How to Apply
Fly sprays should be applied to clean horses, to make sure they aren?t blocked by dirt, dust or heavy sweat buildup. If you’re just doing a quick spritz, odds are You’ll be disappointed with the results. These products work by a combination of external presence on the hair and the chemical circulating in the horse.
Manufacturer?s directions vary from ?spray lightly? to use 6 ounces or ?generous amounts? and be sure to work against the hair to get down to skin level. We had the best results with working against the hair and getting down to skin level, but this takes time to do correctly.
Be careful not to use two different sprays at the same time on your horse. Although we all do it, it’s best not to use Spray X on one day and Spray Z on the next without bathing the horse between. You could risk a chemical reaction.
Always do a 24-hour spot test when using a new product on your horse, especially if He’s at all sensitive. And be aware that other people or horses in the barn may be allergic to some ingredients, such as cedar oil.
Our Trial
We used sprays according to instructions and observed effectiveness indoors and outdoors. The results are based on both duration of effect and effectiveness in keeping insects away. Moderately effective = 75% or less reduction in insects landing. Highly effective was 75% or higher reduction in insects landing.
Products described as short-lived were effective for four hours or less. Several products were found to be highly effective, but they varied quite a bit in how long they lasted.
Note: Results also depend upon the bug population in the area at the time you use it and, to some extent, the sprays being used in close range of your own barn.
Bottom Line
Farnam?s Mosquito Halt topped the class in detering both biting flies and mosquitoes, both for its duration of activity and is fairly priced for products that claim extended duration of effects.
Our Best Buy, Repel-X Emulsifiable concentrate, is also highly effective but with a shorter duration of activity. If you don’t want to mix a spray, Zonk-It! is the runner-up for Best Buy.
Sensitive-skinned horses may do best with SuperShield Red.
Eleanor Kellon, VMD
Veterinary Editor
