31 March 2000


What can be done to control

sheep ectoparasites now

that organophosphate

products have been

removed from the market?

Independent sheep

consultant Lesley Stubbings

gives her view

AGAINST a background of more outbreaks of sheep scab and lice, the temporary withdrawal of organophosphate (OP) dips from the market last December will leave many flockmasters literally scratching their heads this season.

At this stage, it is impossible to say when new containers will be available. But given the time it takes to test new packaging, it is unlikely we will have any OPs on the market until 2001.

Like it or not, the OP compounds are still the best treatments because of their high level of efficacy – over 99% – their broad spectrum and persistence, so 2000 could be difficult. The fact that over half of all sheep ectoparasite treatments were OPs last season says it all.

You may not have used OPs for some time, but the risk of scab mites or lice getting into the flock are going to be higher this year, because those who sell replacements, stores and other sheep will be less able to control the problem. You must plan ahead and consider the options carefully:


&#42 DIPS

The only dips left on the market this summer will be the synthetic pyrethroids (SPs). These are either cypermethrin or flumethrin.

Their use has dropped by 70% over the last couple of years, partly due to higher costs, but largely because they pose a much higher risk to the environment. We must try to use these products carefully and sparingly.

Cypermethrins are active against sheep scab and lice, but only as a treatment – they do not protect. Flumethrin will not give cover for blowfly, but does give some protection against scab. They are not authorised for use in jetters or showers; there is a serious risk that resistance of both scab mites and lice will be accelerated if they are used off-label this way.


There are two main categories of pour-on. The cypermethrins will control all ectoparasites except scab, for four to eight weeks. Many farms with tick problems have started to use these products successfully for tick control, particularly in the spring. They will also control lice well if they are used just after shearing, giving the added benefit of blowfly control.

Cyromazine (Vetrazin) is an insect growth regulator (IGR) which means it stops blowfly larvae developing into a strike. It gives a long period of protection, about eight to 10 weeks, against blowfly and is now used widely, particularly in lowland flocks.


Use of these products has increased rapidly over the last couple of years and we are going to rely more heavily on them this year for scab control than ever before.

It has to be said that in the past, results on farms have been mixed. I think this is largely due to the fact that their uses and limitations have not been properly explained. Before you decide to use them this year, consider these important facts:

&#8226 Diagnosis – many apparent failures are due to misdiagnosis. These products will not treat lice. Without a proper diagnosis you could be wasting your time and money.

&#8226 Persistence – only moxidectin can protect sheep against scab (28 days). Besides moxidectin, the others have no claims for persistence. To prevent re-infection you must put treated animals in a field or building which has had no sheep for at least 16 days.

&#8226 Dose Rate – ivermectins must be given twice – dont be tempted to give just one injection. Doramectin only requires one dose, as does moxidectin unless you are treating a scab outbreak.

&#8226 Handling – take your time. One missed animal will keep the scab going and you will be back to square one. You must treat all animals in a group; not just those that look affected.

Flockmasters may have to look for alternative ectoparasite treatments with the temporary removal of OPs.

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