Cypermethrin leaves few options

Controlling scab, lice and ticks has become harder for sheep farmers in recent weeks, with the suspension of marketing authorisation for dips containing cypermethrin.

Removed from sale because of environmental concerns, cypermethrin-based dips have been a part of the industry’s armoury for more than 10 years and have proved highly effective in controlling ectoparasites.

However, a lack of management of dipped sheep and spent dip has led to several cases of watercourse pollution, says Bob Merriman of the Environment Agency.

Ectoparasite control in a world without cypermethrin-based dips will rely on just two groups of products, says SAC vet Brian Hosie.

“Now we’re totally reliant on organo-phosphate dips and moxidectin and doramectin injectibles.”

While these products are currently effective, Mr Hosie believes increased reliance on them could promote resistance among parasites, meaning their effectiveness would be compromised in years to come.

“To ensure products remain effective farmers must ensure they are used properly, with correct dose rates used and, in the case of dips, sheep submerged for the recommended time.”

With increased risk of resistance building up, independent consultant Lesley Stubbings says producers must use the macrocyclic – lactones (MLs) group, which includes endectocides, more carefully when controlling both endo and ectoparasites.

Obtaining an accurate diagnosis before attempting to treat scab will be vital.

“Too many sheep are treated on the basis that producers think they have scab.

When you get it wrong it’s a waste of time and money, a risk to sheep health and increases resistance in future.”

Mr Merriman says farmers may also be able to make better use of pour-on products to prevent blow-fly strike in early and mid summer instead of relying on dipping at this time of year.

When using injectible products there are two key rules which must be followed, adds Mr Hosie.

“Firstly, sheep should be weighed to ensure the correct dose is given and secondly, the injection must be given by the correct means.

There is no point giving an injection which is designed to be used sub-cutaneaously by the intra-muscular route and vice-versa.”

On the dip front Mr Hosie believes more work needs to be done to investigate ways of de-activating dips before disposal.

“Historically, there were products which de-activated the active ingredients in dips, but these are less common now.

“There is also a danger of farmers making more use of spray races and jetters.

This must be avoided as these often fail to ensure a 100% kill and hence will increase the chances of resistance developing to organo-phosphate products.”

Mr Merriman says mobile dips should be sited well away from watercourses and drains.

“In the past mobile dips have been used in farm yards and farm lanes.

While this may make handling sheep easier, these areas often have drains, so run-off happens much quicker and dip solution can easily enter watercourses.

Additionally, an authorisation to dispose of used dip is still needed.”

Independent sheep vet Chris Lewis is disappointed the ban has come while a consultation was already in progress and when practical steps could have been put in place to help reduce risk of pollution.

“Penalties could have been issued more heavily for poor use of dips to highlight best practice methods and a withdrawal period to allow for retention in fleeces could have also been issued,” he reckons.