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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.

Ticks are becoming more abundant due to changes in farming practice, climate change and acaricide resistance.


Sheep scab is caused by a tiny, pearly-white mite (Psoroptes ovis) just visible to the naked eye. 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.


Crovect® Pour On

When looking for wider ectoparasite control, Crovect is the market-leading1 synthetic pyrethroid, offering sheep treatment and control options for ticks, biting lice, headflies, and blowfly. Crovect can be used for the treatment of tick infestations with a persistent efficacy of 10 weeks.

Crovect Pour-On is a versatile, easy to use synthetic pyrethroid (SP) for the treatment and control of headflies, ticks and treatment of biting lice on sheep. Crovect can be used for the treatment of tick infestations with a persistent efficacy of 10 weeks. It is also licensed for the treatment and prevention of blowfly strike and has the added benefit of an eight-day meat withdrawal, offering flexibility to market.

Product benefits

  • Long lasting protection for ticks
    • Treats tick infestation with a persistent efficacy of 10 weeks
    • Ticks cause health and welfare issues if not controlled
  • Trusted by farmers
    • The number one synthetic pyrethroid1
  • Convenience
    • 8 day meat withdrawal period
    • Provides protection against wider ectoparasite control including maggots, headfly, lice and blowfly strike
Crovect Pour-On 5L

Dectomax® Injection

Dectomax Injection treats and control sheep scab in a single injection.

Product benefits

  • Single injection endectocide
    • Treats worms and scab with a single intramuscular injection
    • Licensed for Psorptes ovis – the causal mite of sheep scab
  • Ideal as part of a quarantine dose
    • Can be used as part of sheep scab and worm control around lambing
    • Broad spectrum
    • Kills benzimidazole-resistant worms
  • 70 days meat withdrawal period
Dectomax injection