Saturday, August 24, 2019

Watch out for surge of head flies as autumn beckons

August 8, 2019 by  
Filed under Livestock

Farmers are warned to look out for the annual emergence of head flies on cattle at pasture – linked with the transmission of summer mastitis in dairy cows and heifers.

A major source of annoyance for cattle, head flies cause considerable irritation as they feed on proteins from secretions such as saliva, tears, sweat and milk, and use this to mature their eggs.  They remain a problem until colder autumn weather kills them off.

“Head flies hang around in woodland and travel to and from the cattle several times a day,” explains John McGarry, a fly specialist at Liverpool University’s Institute of Veterinary Science and contributor to the Control of Worms Sustainably (COWS) Guide to insect pests of cattle.

Carnivorous larvae

“The males die a week after mating and the females lay batches of eggs in the soil during August and September. These turn into carnivorous larvae which feed on insects in the ground. They grow slowly for ten months before emerging the following summer as adult flies.”

Cattle affected by head flies move to the shade, are restless and may stamp and swish their tails. This leads to less time spent grazing and decreased performance – including links to summer mastitis as they feed on secretions from the teats.

“Treating head fly infestations is usually through applying synthetic pyrethroid chemicals,” says Dr McGarry. “But avoiding grazing on wet, low-lying fields near woods from July to September may reduce head fly numbers. Stock should be checked at least once a day.”

Control

Chemical control may include insecticide-impregnated ear tags which give five months cover and should really have been applied at turn-out; and pour-on treatments or knapsack sprays, which need re-applying, depending on fly numbers and any heavy rainfall.

Alternatively, teat sealant can be applied to pregnant heifers and dry cows can help stop the spread of summer mastitis bacteria by flies. Garlic licks, fly trapping and the use of fly predators, may offer some form of control, but there is little evidence to support this.

Treatment costs vary from £3 per ear tag to 50p/dose for a pour-on – which may need doing several times in a season. Farmers should gauge how much performance is being lost – remembering the labour required to treat animals, says Dr McGarry.

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