Ectoparasite Welfare Management in Sheep
Ectoparasite Overview
Key external parasites of sheep include: blowfly (Lucilia sericata — causing flystrike); sheep scab mite (Psoroptes ovis — causing intensely pruritic scab disease); lice (Damalinia ovis — causing pruritus and wool loss); keds (Melophagus ovinus — bloodsucking wingless flies); and ticks (Ixodes ricinus — causing tick worry, blood loss, and disease transmission). Each causes welfare harm; blowfly and sheep scab are particularly significant.
Sheep Scab: Welfare Crisis
Sheep scab (psoroptic mange) causes intense pruritus: affected sheep bite, scratch, rub, and 'keel' (roll on their backs) to alleviate itching. Body condition deteriorates rapidly; wool loss, skin excoriation, and secondary infection follow. Untreated, scab progresses to severe welfare compromise and death. It is notifiable in the UK (obligation to report to APHA). Treatment requires macrocyclic lactones (ML: ivermectin, doramectin injection) or plunge dipping (organophosphate or ML pour-on formulations).
Louse Infestation
Louse infestation causes pruritus, wool damage (staple breakage), and reduced growth. Heavy infestations cause 'scruffy' fleece and visible louse populations in parted wool. Lice are host-specific (sheep lice do not infest other species). Treatment with synthetic pyrethroid pour-ons or plunge dipping is effective. Biosecurity (preventing introduction via sheep from other flocks) reduces risk.
Tick Management in Sheep
Sheep ticks (Ixodes ricinus) are the primary vector of louping ill, tick-borne fever, and tick pyaemia in sheep. Lambs are most severely affected. Tick management combines: acaricide treatment (dipping, pour-ons) at high-risk periods; pasture management (reducing bracken and rank vegetation); grazing management (resting heavily infested pasture); and vaccination against louping ill where appropriate.
Integrated Ectoparasite Management
Routine blanket ectoparasite treatment drives resistance. Integrated management involves: regular inspection and appropriate use of monitoring tools; targeted treatment of affected animals; selection of effective actives (rotating classes, using strategic dipping where practical); resistance management (avoiding prophylactic treatment without evidence); and biosecurity (quarantining incoming sheep, treating before integration). A flock ectoparasite management plan agreed with the flock vet is the gold standard.