Less dipping means lice infestation

By Emma Penny

WIDESPREAD lice infestation in cattle and sheep is proving a headache for producers, while vets and animal health companies have also experienced an upsurge in lice cases and enquiries.

Aberdeenshire vet Robert Loggie of the Polesburn Vet Clinic, Methlick, says he has seen many cases of lice this winter, particularly in cattle.

That is echoed by Merial company vet Andy Forbes, who says his company has carried out more investigations into lice this year.

Cyanamids Colm McGinn believes it is likely to become a greater problem, particularly in sheep, while Pfizer vet Steve Fay says it was the second greatest concern after lungworm for cattle producers at a recent company meeting.

Experts believe there are several factors involved in the increase: Less dipping and the removal of organophosphorous products from the market, rising use of injectable products, wrongly identifying the parasite involved, and poor management when treating stock.

The end of compulsory dipping heralded the start of a rise in lice in sheep, believes CVL entomologist Peter Bates.

“Dipping was an important factor in control, and now regulations have been relaxed, the lice population has expanded.”

Sheep consultant Lesley Stubbings adds that removal of OP dips from the market will increase concerns.

“It will be difficult to control lice – and scab – without OP dips.

“While synthetic pyreithroid products will control lice in sheep, we need to avoid any potential resistance concerns, as SP resistance is a huge problem in Australia.”

Rising use of injectable products is likely to be another key reason for the rise, says Mr Bates.

“More producers are using these products for worming stock and controlling ectoparasites.

“But while they will kill blood-sucking lice, they wont affect chewing lice.”

This means flockmasters treating sheep with an injectable must be aware that while they will control scab, these sheep may still carry lice, warns Ms Stubbings.

“An SP pour-on will control lice, but wont be that effective on a fully-fleeced sheep.”

Mr Bates adds that where fully fleeced sheep are infested they may require dipping.

“This will give some protection from reinfestation for five to six weeks, and will kill the entire population.

“Lambs can be treated with a pour-on, and where infestation is bad, they should be treated twice, and according to label recommendations.”

Cattle producers using injectibles have also suffered lice problems, says Mr Fay, adding that it is a fault of injectibles as such.

He says pour-on or spot-on products with a good persistence are the only option for controlling chewing lice in cattle.

Mr Loggie agrees, and is advising cattle producers with a herd lice problem to use such products.

“It is too expensive to worm again, and these spot-on or pour-on products do seem to be working.”

Clipping the backs of cattle may offer a degree of control says Bristol University researcher Ailsa Milnes, who believes lice infestation is often under-estimated as a problem on-farm.

She also adds that her research into lice in cattle has found that chewing lice are far more prevalent on beef cattle, where they may account for 70% of an infestation, than in dairy cows.

This means it is essential to identify which lice species is responsible for problems before treatment.

According to CVL parasitologist Mike Taylor, chewing lice are brown, with a round head, while sucking lice have a pointy head and are a red or blue colour, depending on the species.

“It is best to pull lice off cattle and identify them either through your vet or local VI centre.”

For sheep producers, identifying the cause of itching before treatment is even more vital, says Ms Stubbings.

“Find out whether your sheep have scab or lice; many producers have treated itching sheep for scab, only to find treatment does not work because lice is the problem.”

But poor management at dosing may aggravate concerns, warns Mr Forbes.

“Where stock still have both chewing and biting lice after treatment, under-dosing may be a problem. Also, all animals in a group, or in contact with a group, must be treated to prevent reinfection.”

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