They may trigger conjunctivitis and headshaking. At worst they can contaminate wounds or in some countries they can spread diseases, such as West Nile Virus, which can be fatal. It is thought that flies may be responsible for the spread of sarcoids, while the biting midge, Cullicoides species, is responsible for sweet itch, a debilitating allergic condition. Flies can also carry other parasites that can infect the horse such as Habronema species and Onchocerca cervicalis, which can affect the skin and sometimes the eye.
The good news is that there is much that we can do to help stop the irritation caused by flies. Zoetis vet Wendy Talbot has put together six important tips to help you keep your horses fly-free this summer.
Know your enemy: Horses are prone to attack from many species, including house flies, horse flies, black flies, blow flies, bot flies, mosquitoes and midges. Knowing the type of fly that is causing a problem can be useful in deciding how best to control it.
Keep stables, yards and paddocks clean: Most flies thrive and breed in warm, moist conditions such as on dung, rotting bedding or spilt feed material. 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 and spreading bacteria.
Keep your horse clean: A well-groomed horse is less attractive to flies so it pays to make extra effort with your daily grooming to remove mud and stable stains. Also remember to keep nostrils, eyes and dock clean.
Use fly rugs and masks: These have become essential pieces of kit for many horses during the summer. Applying a fly repellent or insecticide to the rug can make it even more effective.
Use repellents: These aim to make the horse less attractive to the fly and will usually need reapplying frequently.
Take control with insecticides: These have a medicinal function; aiming to kill the fly as soon as possible after contact, with no biting needed. 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 four active ingredients contained in insecticides currently licensed for use on horses in the UK are: Pyrethrum which belongs to a group of chemicals known as pyrethrins, derived from the crysanthemum flower; cypermethrin and permethrin which are synthetic forms of the natural pyrethrins belonging to a group known as synthetic pyrethroids and benzyl benzoate which is formed from benzyl alcohol and benzoic acid. Cypermethrin has the longest expected activity of horse insecticide ingredients currently available. It is a prescription only medicine and may control files for up to four weeks.
“Taking control of flies early makes it easier to maintain control throughout the summer, explains Wendy Talbot. “Keeping yards, stables and fields tidy as well as keeping your horse clean makes them less attractive to flies and can help curtail problems from the outset. Using good fly rugs, masks, insecticides or repellents will help keep your horse comfortable over the summer.”