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Fly control for cattle

Sylvaine Lacrosse BVetMed MRCVS, Molecare Veterinary Services

There are few things more frustrating for cows than flies constantly pestering them. However, this nuisance can go far beyond a superficial irritation, leading to significant production losses including reduced rates of weight gain and the transmission of various diseases.

Typically, problem months for flies are between May and August, however UK weather is pretty unpredictable! Some years expect fly problems to start as early as April and/or last into October.

The most common treatment is spot-ons/pour-ons, preventing any winged flies, midges or other ectoparasites from burdening the cattle.We should however, note that only 15% of the fly population have wings, therefore an integrated approach should target both the adult and immature parts of the life cycle. We can separate these target areas into on animal control and environmental control.

Environmental control pertains to the major fly breeding sites on farm, which we can usually minimise by good hygiene. Optimal breeding sites require a warm, humid environment, hence sites heavy on manure, such as calf hutches, act like fly factories in the summer. It is essential to have efficient dung management and drainage to prevent any stagnant pooled effluent. Simple identification, removal and physical destruction of potential fly breeding sites are the first step in an integrated fly control plan.

Chemical methods also play a role when it comes to environmental fl y control. The use of larvacides would kill the larva (maggots), preventing them from ever developing into flies. Larvacides are best to use in areas where urine, faeces and feed are found. Speak to your vet or SQP about which larvacidal products would be most appropriate for use on your farm.

Environmental control also involves the use of adulticides, products which kill adult fl ies. These include your classic fl y sprays and residual products which continue to kill fl ies post-application. With regards to tackling adult flies, areas of application include milking pipes, windows, lights and wherever you see an accumulation on farm.

On animal fly control

Pour-on/spot-on products are by far the most popular treatments available. There is a wide array of products available, with differing lengths of action, ease of application, targeted ectoparasites and cost. Speak to your vet or SQP and together decide which would be most benefi cial for your farm. Whilst the pour-ons/spot-ons are very effi cient at preventing fl ies from targeting the cattle, they do not necessarily reduce the total fly burden on farm. Using both environmental and on animal control, we can tailor an integrated fly control plan to the needs of the farm, in order to break the fly’s life cycle.

What are the main production losses that flies cause?

Reduced weight gain

A decreased voluntary feed intake is associated with a high fly burden. Calves are particularly vulnerable and can suffer reduced feed efficiency, affecting their future health and productivity.


We usually associate Summer mastitis with flies, however biting flies have also been shown to spread staphylococcus aureus mastitis, while the house or stable fly can spread coliform mastitis such as Ecoli.

Newforest Eye (Pink Eye)

The bacteria moraxella bovis causes corneal lesions and is transmitted by the face fl y. Infection can lead to blindness and in severe cases, rupture of the eyeball, a severe welfare concern. Bluetongue, Schmallenberg, etc Transmitted by midges. Midges need a similar control strategy to flies.

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