1 December 1995

Confusion is

rife on scab

WIDESPREAD confusion among sheep farmers over exactly what level of protection is afforded by the range of scab treatments now on the market is undermining effective control of the disease.

So says Peter Bates, head of entomology at the Central Veterinary Laboratory. He points to incorrect dipping procedures and a lack of awareness over risks of re-infection.

"While sales of newly introduced non-OP dips have been high, many producers remain unclear about the level of protection such products can achieve.

While many flockmasters have turned to these non-OP treatments for reasons of health and safety, its clear that unless they are fully conversant with the product their dipping may well be a complete waste of time in terms of sheep scab control."

Mr Bates says an OP dip used on sheep carrying 1cm of fleece will kill existing scab mites and will give guaranteed protection from further infestation for a minimum of three weeks providing the sheep have been dipped correctly.

"Where an OP dip is used on fully-fleeced sheep, treatment will kill existing scab mites and afford a further three weeks of protection against infection or longer. Sheep treated with an OP dip will be protected against blow-fly strike.

"However, when it comes to other scab treatment products, this is where many flock owners are believed to be inadvertently failing in controlling scab," he says.

"Non-OP dips containing Flumethrin (a synthetic pyrethroid) will kill existing scab mites and give protection for three weeks on sheep carrying 1cm of fleece. At least six weeks protection will be given to fully-fleeced sheep but in neither case will these products give any protection against blow-fly strike."

Non-OP dips based on high cis Cypermethrin compounds (a synthetic pyrethroid) will kill any existing scab mites but give little residual protection against scab.

Some of the most popular non-OP dips introduced this year fall into the Cypermethrin category. "Unfortunately many farmers are not fully aware that they give little residual protection against scab which is why it is essential that sheep dipped in these compounds must not be turned back onto the field from which they came for at least three weeks," he says.

"A second dip within 14 days of the first is also recommended by the manufacturers to cope with mites emerging from eggs after the first treatment, though many farmers say this is not made clear enough on the manufacturers instructions," he adds.

"The scab mite is able to live for up to 16 days away from sheep and can still be a source of re-infection if sheep treated with non-OP Cypermethrin-based dips or injectables are allowed to rub against fences or gates that may be carrying live mites."

Mr Bates says that the Cypermethrin dips do give protection against blow-fly strike.

"Licensed injectable forms of scab treatment will kill the existing scab mite but offer little residual protection and no protection against blow-fly strike. In the case of Ivomec it is essential two injections are given seven days apart.

"While good advice and information on scab dips is often gleaned by farmers from their agricultural suppliers it is important that sheep farmers discuss sheep scab control with a vet to ensure the correct treatment is used to deal with specific parasitic conditions," he says.

"Producers who chose to use mobile dippers must ask if the dip used was OP or non-OP and if it was non-OP then it is vital that its "category" is known," he warns. "Only then can farmers know if the dip affords any residual cover.

"At the moment there are sheep needing a second treatment that arent getting it and those being turned back into the same field are being put at high risk of re-infestation rendering the intial treatment totally ineffective."

Peter Bates:"Sheep producers must discuss scab control with a vet to ensure the correct treatment is used to deal with specific parasite conditions."

Unless producers are fully conversant with how to use each product, their dipping may be may be a waste of time in terms of scab control.