News & Advice

Lice in Sheep – Why Bother?

Jun 5, 2019 | Dry stock, Dry stock animal health & welfare, Sheep

Lice are external parasites that can live on most animals. They are very host specific, therefore sheep lice will only be found on sheep. While lice are common on many animal’s it is important that we take care to manage them on our sheep to help prevent “outbreaks”. Keeping lice levels under control not only ensures your sheep are happier, but they should also produce more wool, that is of better quality.

Key facts about sheep lice:

  • Lice complete their entire lifecycle on the sheep.
  • They usually spread via direct contact between sheep e.g. Yarding, lambs suckling, rams mating, mobbing behaviour.
  • They prefer conditions where it is cool and dark, hence why lice are more common over winter and in long woollen sheep.
  • Shearing removes about 30-90% of lice, this is the most effective time to achieve control through chemical lice treatment application.
  • Lice are pale brown in colour and about 1.5mm long.


Impact of lice infestations:

  • Lice cause irritation and rubbing, sheep will bite at themselves and rub against anything that is available.
  • Rubbing damages the fleece by matting the fibres and tearing the tip of the staple.
  • Decreased yield and quality of wool could cost you 20 cents per 1kg of wool.
  • Lice infestations can increase the likelihood of flystrike.
  • Lice do not cause ill-thrift, but lice infestations increase significantly in ill thrifty animals.
  • Lice infestations are both an economic and a welfare issue.


Management and Control

  • Lice control is best achieved by combining animal management and chemical insecticides, which is why many farmers choose to treat straight off shears.
  • An annual lice control treatment is important to prevent “outbreak infestations”.
  • Lice are easiest to kill on short wool sheep in late summer when the numbers are low.
  • Pour-on treatments need to be applied to neck and withers and applied to both sides of the body. When used correctly they are highly effective and easy to use.
  • Under-dosing due to underestimating the animal’s weight or not allowing for long wool will result in treatment failure.
  • Synthetic pyrethroids take 6-8 weeks to kill all lice so don’t mix the treated animals with non-treated animals. You need to treat the ram and all introduced sheep.
  • Saturation dipping with just about any insecticide will kill all the lice.
  • The withholding time for wool is voluntary. If you get an infestation, you will need to treat and only the meat withholding is obligatory.

For further information, or product recommendations please contact your local Anexa clinic.

Share This