The Importance Of Fly Control & Treatment

Recent weather conditions have been ideal to produce high numbers of flies, as the eggs and larvae do well in warm wet conditions leading to a population explosion. Flies can cause or contribute to many different diseases. Learn more about control and treatment

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Summer is here and the temperatures have been high, but we are still having plenty of wet weather.

These conditions have been ideal to produce high numbers of flies, as the eggs and larvae do well in warm wet conditions leading to a population explosion.

Flies can cause or contribute to many different diseases, for example blowfly strike (which unfortunately we have already seen several cases of this year), summer mastitis and New Forest eye.

Fly Control

Controlling flies will help control all these diseases. The recent mild winters mean many flies and eggs will have survived the winter and so a greater number will have been around to reproduce this spring.

It is important to have an all-encompassing approach to fly control rather than a reactive, “I have a problem, now what do I do?” approach.

Dairy cattle will come across two distinct insect populations; those found at pasture and those that are in and around the collecting yards and milking parlours. Ear tags and pour-ons are good at controlling flies in grazing herds as they kill biting flies, but are less effective against non-biting flies that feed on the skin and surface fluids as they may not receive a lethal dose.

It is necessary to have different control methods in and around the milking parlour – ultraviolet lamps, fly paper and insecticidal paint are all options.

Flies breed in organic matter, so if everywhere is clean and free from manure, waste food and dirty standing water, they will struggle.

Efforts to eliminate organic matter around the farmyard are also useful to control rats and other vermin, while having clean premises will reduce the risk of bacterial diseases like digital dermatitis.

For cattle, we have a good price on Spotinor at the moment (WHP 0d milk, 17d meat) which will help prevent flies for 4-8 weeks. A 2.5L pack, which will treat 250 animals, is £150+VAT.

Blowfly Strike

Post-calving cattle are especially at risk from blowfly strike if the vulva is torn or inflamed. Any wounds will also be a risk for fly strike. We try to avoid doing any bloody procedures at this time of year (e.g. castrations and dehorning) to limit the risk, but we will apply fly control at the time of any unavoidable surgeries such as a displaced abomasum or a caesarean.

Blowfly strike can easily kill sheep. In animals that survive there can be significant hide and fleece damage, and the body condition of the animal often suffers. The usual suspect is the green bottle fly (Lucilia sericata). Control is multifactorial and requires good flock management and chemical treatment. One adult can lay 200 eggs in one go, which hatch within 24 hours. This means that within a single day a sheep can go from looking clear to being riddled with maggots. This is why it is vital to check your sheep at least daily.

Blowfly Strike Risks

Blowfly Strike Control Strategies


Plunge dipping provides up to eight weeks protection, but it is labour intensive and requires good maintenance of the dip solution to eliminate the risk of faecal contamination and remain effective.

Pour-on treatments with pyrethroid and insect growth regulators have advantages in requiring less handling and may give longer protection. Their main disadvantage is if applied before shearing the active ingredient will be lost with the wool when it is cut off. The control regime with the most success in reducing fly strike losses and death is an early ewe treatment (pre-shearing) with a short-acting product, followed by a treatment after shearing with a long-acting product. The lambs should have a long-acting product at the start of the season, which will protect them for the majority of the summer.

Insect growth regulators kill the young larvae so are no good once an infection has become established but work well for prevention. As well as flock treatment, farmers should try to identify and treat the animals most at risk. Flies are attracted to sheep mainly through their sense of smell, so individuals with conditions such as faecal soiling of the rear end caused by heavy worm burdens or foot rot are likely to be targeted by flies. They should thus be treated for these predisposing conditions to reduce the risk of infestation.

Animals which are affected with blowfly strike need to be clipped and cleaned. The larger maggots need to be removed and placed into either spirit or bleach to kill them. The animal will be painful and there is a big risk of infection. Treat with antibiotics and anti-inflammatories to help with the discomfort. Topical treatment can be used to kill any of the smaller maggots that are not visible yet.

Fly strike and other fly-related diseases have considerable cost and welfare implications, so should be controlled from early in the season. Prevention is definitely better than cure when it comes to flies. An animal that dies as the result of fly strike could lead to prosecution under animal welfare legislation.

Please contact us at the surgery if you would like to discuss any of this or for help with prevention.

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