Sheep Flystrike: Prevention and the Pain of Myiasis

Flystrike (myiasis) causes some of the most severe acute suffering in sheep farming. Prevention is effective and moral obligation demands its prioritisation.

Key Facts

Flystrike occurs when blowflies lay eggs on sheep — usually on soiled or damp wool — and larvae burrow into flesh
Untreated flystrike is fatal within days — larvae release toxins and cause extensive tissue destruction
An estimated 1-3% of sheep in the UK are affected annually, representing hundreds of thousands of animals
Dag score (faecal soiling of wool) is the primary risk factor — management to reduce soiling prevents most cases
Mulesing — surgical removal of skin folds around the breech — prevents flystrike but causes acute pain
Non-mulesing alternatives including selective breeding for low wool wrinkle and topical preventatives are effective
Daily visual inspection during risk periods (spring and summer) enables early detection and treatment

Welfare Considerations

Flystrike causes some of the most severe and rapid-onset suffering in agricultural animals. Within 24-48 hours of egg-laying, larvae begin destroying living tissue — the pain is intense and constant, and untreated animals deteriorate rapidly. The welfare failure of late detection or inadequate prevention is particularly serious because effective preventative measures are available and well-understood. The mulesing controversy illustrates a welfare trade-off: the procedure causes acute pain but prevents a potentially more severe chronic condition. Non-mulesing alternatives, now demonstrated effective at scale in Australia, offer a path to preventing both flystrike and the pain of surgical prevention. Regular monitoring and appropriate use of topical preventatives remain the most immediate welfare tools.

What You Can Do

Inspect sheep daily during warm months when fly activity is highest
Act immediately if any sign of flystrike is detected — this is a veterinary emergency
Manage dag and wool contamination through regular crutching and targeted nutrition
Support wool brands that have committed to non-mulesing production
Advocate for selective breeding programs that produce naturally low-wrinkle sheep