Ectoparasites in Sheep: Welfare Guide
Ectoparasites cause some of the most severe and sustained welfare suffering in sheep. Blowfly strike in particular can progress from undetected infestation to death within 24-72 hours, and the suffering it causes before detection is significant. Proactive prevention is a welfare imperative.
Blowfly Strike
Blowfly strike (myiasis) occurs when blowflies (primarily Lucilia sericata in the UK) lay eggs on moist, soiled fleece. Maggots hatch within hours and begin feeding on the living tissue of the sheep, releasing toxins that cause systemic illness and rapidly penetrate deeper tissues. Affected areas develop characteristic foul-smelling, discoloured, and liquefied tissue — intensely painful and debilitating.
Prevention includes: regular inspection during high-risk periods (April-October); dagging (removing soiled fleece from the breech and tail area); treating diarrhoea and footrot (risk factors for strike); timely shearing; and insect growth regulators or organophosphate products applied to at-risk areas. Treatment involves clipping affected wool, removing maggots, cleaning wounds, and applying appropriate insecticidal products — plus systemic treatment of severely affected sheep.
Sheep Scab
Sheep scab is caused by the mite Psoroptes ovis and is a notifiable disease in Great Britain. The mite causes intense pruritus (itching), wool loss, excoriation, and skin damage. Affected sheep bite and rub themselves constantly, developing characteristic scabby lesions on the shoulders and back. The welfare impact is severe — chronic, intense pruritus is highly distressing. Treatment requires two injections of macrocyclic lactone (ivermectin or doramectin) 7 days apart, or plunge dipping in organophosphate.
Lice and Keds
Lice (Damalinia ovis, Linognathus ovillus) cause pruritus and fleece damage but are less welfare-critical than scab. Sheep keds (Melophagus ovinus) are wingless flies that cause pruritus and reduced fleece value. Both are controlled with licensed insecticide products applied at shearing or subsequently. Resistance to some products is emerging — veterinary guidance on product selection and rotation is recommended.
Tick Welfare
Ixodes ricinus ticks cause direct irritation and transmit louping ill virus (fatal neurological disease in lambs), tick-borne fever, and other pathogens. Pasture management (reduced bracken, improved drainage) and acaricidal treatments reduce tick burden. Tick-borne fever immunosuppression increases susceptibility to other infections, compounding welfare impacts.