Controlling Ectoparasites - Making Best Use of Remaining Treatments


Summary written by Peter Bates PhD, MIBiol, CBiol, FRES
Taken from Moredun Foundation Newsheet Volume 4 No. 14



  • scratching-HerdwickThere are a number of parasites that inhabit the skin or fleece of sheep in the UK. Effective control of these parasites depends on whether the ectoparasite is permanent (i.e. spending its entire life cycle on the sheep) or semi-permanent (i.e. at least one life stage free living).
  • Important permanent ectoparasites include scab mites and chewing lice. Other, less common permanent ectoparasites include ear mites, mange mites, sucking lice and keds.
  • Important semi-permanent ectoparasites include blowfly larvae (strike) and ticks. Other, less widespread semi-permanent ectoparasites include nasal bot flies and head flies.
  • It is vital that all flocks that are suspected of being infected with ectoparasites be examined by a veterinary surgeon and a definite diagnosis reached. Flockowners should bear in mind that sheep may be infected with more than one ectoparasite (e.g. scab and lice) at the same time.
  • If permanent ectoparasites are found on one animal than all sheep in the group should be considered to be infested and the whole group should be treated (not just those presenting with clinical signs). One missed sheep could re-infest the whole group.
  • Good biosecurity can prevent the introduction of permanent ectoparasites in a flock. Good well maintained fencing will also control the introduction of permanent ectoparasites by preventing contact with neighbouring flocks. Quarantine all incoming stock for at least three weeks (if possible) and observe for signs of infestation (nibbling, rubbing, scratching, deranged wool, areas of wool loss etc).
  • Even permanent ectoparasites can survive off the host for a period of time (scab mites and chewing lice for at least 17 days). It is therefore important that all vehicles and trailers used to transport sheep are thoroughly cleaned and disinfected after use.
  • All ectoparasite treatments should be administered strictly according to the manufacturers’ instructions. Dip-baths must be accurately calibrated and where injections are considered sheep should be accurately weighed.



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