Those pesky flies – how you can fight back

Bot eggs on a horse's legs.
Bot eggs on a horse’s legs.

With the heat comes the flies and the annoyance they cause. But adding to the nuisance factor is the increased risk of disease spread.

Horses are prone to attack from many species of “ectoparasite” – parasites that affect animals externally. Culprits include house flies, horse flies, black flies, blow flies, bot flies, mosquitoes, midges, lice, ticks and mites. They can cause dermatitis, pruritic (itchy) conditions, lumps and skin lesions. They can also cause conjunctivitis, headshaking contamination of wounds and have the potential to spread other diseases.

Biting midges, Cullicoides spp. can be a particular bugbear as they are the cause of sweet itch. Mosquitoes are also well known biting pests. Many species are known, including those with the potential to spread diseases such as West Nile Virus, a fatal disease. Flies may also carry other parasites that can infect the horse such as Habronema spp. and Onchocerca cervicalis, which can affect the skin and in extreme cases the eye.

“A good fly control programme is highly advisable during the summer, to help keep your horse happy and healthy,” says Zoetis vet Wendy Talbot.

“We would never put up with fly infestations so why should our horses? If one product does not seem to work well for your horse, consider a different formulation or ingredient.”

A Culicoides biting midge.
A Culicoides biting midge.

Knowing the type of fly that is causing a problem can be useful in deciding how best to control it. In general most flies thrive and breed in warm, moist conditions such as on dung, rotting bedding or spilt feed material. From these unsavoury places they can spread bacteria to the horse, especially to vulnerable areas such as the eye and wounds.

The most effective way to control flies is with a double-pronged approach of good management and a proven fly repellent or insecticide. Frequent removal of droppings from the pasture and stable will reduce fly breeding grounds, while keeping the muck heap well away from stables and paddocks and keeping stables meticulously clean will reduce the risk of flies bothering the horse. Fly rugs and facemasks are essential for many horses in the summer and applying a fly repellent or insecticide to the rug can make it even more effective.

As an owner it can be difficult to choose which fly product will work best. A repellent aims to make the horse less attractive to the fly. An insecticide aims to kill the fly as soon as possible after contact and can remain effective for up to four weeks against some ectoparasites. For maximum effectiveness treatment should be started before the fly season has begun, to control breeding, and continued at regular intervals throughout the season.

The fact that insecticides have a medicinal function by killing the insects, means that in Britain they require a licence from the Veterinary Medicines Directorate, to ensure their responsible, safe and effective use.

Latest research and information from the horse world.

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