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Lice in Sheep

Lice in Sheep

Lice infestation in sheep is primarily caused by the biting louse Bovicola Ovis.

Important facts about biting lice

  • The entire life cycle occurs on the sheep
  • It takes about 21 days from egg production to become mature adults
  • They feed on skin debris and wool scale
  • They prefer it cool and dark hence numbers increase over winter and in long woolen sheep. Most summer shorn sheep will be devoid of lice
  • The ‘effective grazing’ area for the louse increases with bigger sheep (big surface area),more wool, fineness of wool and crinkliness of skin (esp. Merinos)
  • Spread only occurs with dose contact between sheep e.g. yarding, lambs suckling, rams mating, mobbing behavior (Merinos), camping together in sleep camps esp. in cold weather
  • Shearing removes about 30% of lice
  • Found mainly in the shoulder/neck/wither areas
  • Lice are pale brown in colour and about 1.5mm long.

Effects of lice

  • Irritation causing rubbing
  • Decrease in yield and luster of wool
  • One estimate is a cost of 20c per 1kg of wool
  • May pre-dispose to fleece cotting
  • Cockle in pelts is reduced dramatically if effective dipping is undertaken resulting in saving for the leather industry
  • Lice DO NOT CAUSE ILL THRIFT but can increase dramatically in ill thrifty animals.


  • - Sheep rubbing
  • - Part wool in at least 10 sites in shoulder, neck area and check for lice
  • - Examination of fleeces post shearing - ask the rousies.

Problems associated with treatment

  • Pourons can fail for several reasons:
  • Not applied to neck and withers where lice reside and only applied on 1 side of body - use T bar running from the neck to tail along midline.
  • Under dosing due to underestimating sheep weight and not allowing for the increase in ‘effective grazing area’ in long wool sheep.
  • There are some synthetic pyrethroid (SP) resistant lice
  • SP’s can take 6-8 weeks to kill lice so non treated animals in contact within that period can become infected e.g. lambs or ewes.
  • - Saturation dipping with just about any insecticide will kill all lice

Don’t Forget

  • Some fly controls also kill lice so check to avoid overdosing your sheep
  • Lice are easiest to kill on short wool sheep in summer when numbers are low. Long wool sheep in Winter with large lice numbers make treatment difficult.
  • Treat the rams
  • Treat all introduced sheep
  • The withholding time for wool is voluntary. If you get an infestation you will need to treat and only the meat withholding is obligatory.

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