Flystrike in Sheep: Deep Welfare Guide
Disease Mechanism
Blowfly strike (myiasis) occurs when blowflies (primarily Lucilia sericata in the UK) lay eggs in warm, moist, soiled fleece. Hatched maggots feed on skin and flesh, releasing toxins and enzymes that liquefy tissue. Maggot infestations spread rapidly: a small strike can become a major infestation within 24-48 hours if untreated. The affected area expands rapidly, with maggots tunnelling under skin.
Welfare Consequences
Blowfly strike causes intense suffering. Affected sheep exhibit restlessness, stamping, attempts to bite affected areas, tail wagging, and eventually depression and collapse. The penetrating wound and toxin release cause systemic illness (flystrike toxaemia). If untreated, death occurs within days. The suffering is acute, severe, and rapidly escalating. Every hour of delay in treatment increases the degree of suffering and reduces the chance of survival.
Risk Factors and Seasonal Pattern
Risk is highest from April to October (UK), peaking in summer. Risk factors include: soiling of fleece with dung (particularly in darrhoea); fleece length and moisture; wounds (castration/docking sites, foot rot lesions); tail docking status (longer tails trap dung); dense wet fleece; and proximity to warm, humid weather following rain. Some individual sheep are repeatedly struck, suggesting genetic susceptibility.
Prevention
Prevention involves multiple strategies: regular inspection (minimum daily in high-risk periods, twice daily in outbreak conditions); crutching/dagging (removing soiled fleece around the tail); prompt treatment of diarrhoea and footrot; use of preventive insecticide preparations (organophosphate pour-ons, cyromazine products, dicyclanil formulations); fly-dressing to repel blowflies; and genetic selection for less strike-prone traits. High Care Farms monitoring provides a welfare standard for flystrike prevention.
Treatment
Treatment involves: removing all maggots manually and by shampooing; clipping fleece widely around the wound to expose and ventilate; applying insecticide wound dressing; and systemic treatment for flystrike toxaemia (NSAIDs, antibiotics, supportive fluids in severe cases). Severe cases may require euthanasia. Post-treatment monitoring is required for secondary fly strikes and wound healing. Full wound examination should assess the extent of tissue damage before deciding on treatment or euthanasia.