The most common louse in sheep is the biting or chewing louse (Bovicola ovis), which are small, pale to red/brown flat insects feeding on skin debris and hair, living within the centimetre of the wool closest to the skin.
Lice do not produce a definite scab lesion and can be found anywhere on the sheep.
Heavy infestations are associated with sheep in poor health.
Infested sheep rub and scratch and the fleece appears rough and pulled, with numerous loose strands of wool. Sheep can bite and nibble at the fleece. Unlike scab, there is no reflex to nibble at affected areas when they are touched in handling.
Lice populations are influenced by body condition; the lower the body condition scores the higher the population of lice.
Biting lice are a significant indicator of underlying welfare problems within a flock and need to be treated promptly to reduce productivity losses.
Sheep infested with lice
Lice are generally seen in the winter months, the majority between January and March.
- Lice live their entire lives on the sheep, introduced by contact or purchase of infested stock. Lice can, however, live off the sheep for 16 to 17 days in tags of wool, clothing, barns or livestock transport.
- Quarantine incoming stock for at least 3 weeks.
- Ensure fencing is sound – prevent straying on or off.
- Disinfect livestock trailers after use.
- Remove all debris (wool etc) from contaminated housing and do not re-stock for at least 3 weeks.
- As soon as sheep start rubbing and scratching it is important to ask your veterinary surgeon to make an accurate diagnosis by identification of any parasite, and advise on treatment.
- Not involving a vet can be far more costly than a veterinary inspection!
- Interestingly, sheep can also have mixed infections of sheep scab and chewing lice, which is why it is important to make an accurate veterinary diagnosis
- Biting lice can be controlled by using synthetic pyrethroids (SPs) which can be cypermethrin based pour-ons such as Crovect® Pour-on, alphacypermethrin or deltamethrin. Diazinon based organo-phosphate dips can also offer some level of treatment.
This guide is a practical introduction to the external parasites most likely to jeopardise the welfare and productivity of sheep: blowfly strike, lice, ticks and scab.