Fly Control in Livestock 

By Vet Paul Kirkwood

Modern methods of livestock farming have led to an increased need to control pests including flies. 

Public perception of farming is increasingly being scrutinised and having good fly control leads to improved cattle and sheep welfare whilst decreasing the risk of fly-associated diseases. 

Uncontrolled fly populations in cattle can lead to decreased milk yields and reduced calf weaning weights. 

Fly strike in sheep can have a huge economical and welfare impact as it can lead to weight loss and even death if left untreated. 

Flies are attracted to sheep and other livestock mainly through their sense of smell, so individuals with conditions such as faecal soiling of the rear end caused by heavy worm burdens, foot rot or open infected wounds are likely to be targeted by flies. 

These animals should be treated for their predisposing conditions and particular attention paid to their management. 

In addition to being a nuisance to livestock and farmers (particularly towards the end of the summer as biting flies become more prominent), flies also play a role in conditions such as fly strike, contagious “summer” mastitis and eye infections (New Forest Eye).

Fly numbers are determined by factors such as temperature, moisture of breeding habitat and humidity. Summer months and warmer conditions are perfect for a surge in the population of many species of flies. Fly activity can begin as eggs can start to hatch when ground temperatures rise above 7C meaning that the control of fly populations needs to start in the Spring, even before adult flies are seen. 

One female adult fly can produce up to 3000 eggs so by the time lots of adult flies are circulating around livestock, starting to control them is usually too late. 

Manure, areas of spilled feed, areas around water troughs, calf hutches and any areas with moist organic matter are all ideal breeding sites for flies. 

Along with the chemical products (pour-ons, injectables, ear tags and plunge dips), effective control of flies depends on reducing their numbers at the source by removing the organic material in which flies breed. With a life cycle of 1 week, flies can rapidly multiply in small amounts of manure. Clearing up manure and storing it away from the farm buildings, removing waste feed and ensuring good water and slurry drainage will help reduce insect breeding sites. 

In order to minimise the impact flies have on your flock or herd, a multi-modal approach to fly control is essential. 

Chemical treatment on a regular basis will help to keep existing and future emerging fly populations under control. An appropriate choice of fly treatment will vary according to the length of period of activity required and the management policies on the farm. 

Although plunge dipping for sheep has traditionally been a summer activity to provide protection, it is labour intensive and may be better reserved for autumn treatments and scab control. 

Pour on treatments with pyrethroid and insect growth regulators have advantages in requiring less handling and these products provide varied lengths of protection. 

Early intervention is imperative and the correct and careful application of these products maximises their effect. For more details speak to your vet about creating a fly control plan on your farm.