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Ensuring sheep are at optimum health is important for welfare and productivity benefits. Ectoparasites such as lice, ticks, scab and headflies can cause disease and distress, so it is important to know how you can control these diseases.



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. Lice can be confused with sheep scab. However, unlike scab, there is no reflex to nibble at affected areas when they are touched in handling.

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.

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.


Ticks can have significant effects on sheep welfare and production, and recent studies suggest ticks are becoming more numerous and widespread throughout the UK.

In sheep, they transmit three important diseases:

  • Louping ill - symptoms are wobbly gait, trembling, seizures or even sudden death.
  • Lamb pyaemia (“cripples”) - resulting from infected tick bites, can cause lameness, paralysis, ill thrift and death in young lambs
  • Tick borne fever (TBF) - causes reduced immunity (respiratory / joint infections) and reproductive problems
Ticks are visible to the naked eye on sheep and lambs and are generally active from March until October (with peak times in Spring and Autumn) depending on the area and weather.

Ticks favour dense, damp habitats, eg. rough grazing, heath or woodland. The thicker the vegetation the heavier the tick population.


Sheep scab is caused by a tiny, pearly-white mite (Psoroptes ovis). Mites live on the skin surface causing a skin allergy to their droppings. Initially the lesions are very small (less than the diameter of 1p coin) as the mites multiply the scab spreads, eventually covering the whole sheep. Mites can be found around the edge of the growing lesion.

Early disease is difficult to spot – animals look and behave normally. However, as the scab spreads sheep become increasingly irritated, excessively rubbing, scratching and digging with their back legs. After 10 to 15 weeks the scab covers the entire animal. Wool can fall out, revealing a dry, scabby skin beneath. By now scab can have spread throughout the flock making control expensive. Infested animals can demonstrate a violent biting reflex on handling (similar to scrapie) sometimes leading to fitting.

Scab can be found throughout the year, but the majority of cases occur between October and March. Scab mites live their entire lives on the sheep, introduced into a flock through contact or purchase of infested stock. Mites can however live off the sheep for 16 to 17 days in tags of scabby wool, clothing, barns or livestock transport.