Sheep Blowfly Strike Genetics: Breeding for Resistance

Blowfly strike is a painful, potentially fatal condition in sheep; selective breeding for resistant traits offers a sustainable prevention strategy.

Key Facts

Lucilia sericata is the primary blowfly causing strike in UK sheep; it lays eggs in moist, soiled fleece areas.
Strike can kill sheep within 3 days if untreated; affected areas show maggot infestation and tissue destruction.
Wool characteristics associated with resistance include shorter, cleaner fleece around the breech area.
The Merino breed's heavily wrinkled skin causes excessive fleece moisture and high strike susceptibility.
CSIRO research in Australia has identified genetic markers associated with reduced strike susceptibility.
Mulesing — removing skin around the breech — reduces strike but causes acute pain; alternatives are being developed.

Welfare Considerations

Blowfly strike causes intense pain, distress, and rapid physical deterioration. Prevention through genetic selection for resistant fleece traits reduces dependence on chemical insecticides and surgical interventions such as mulesing. Producers should integrate genetic resistance selection into breeding programmes alongside management measures — including regular inspection and prompt treatment of any cases that occur.

What You Can Do

Inspect sheep fleece regularly during blowfly season, particularly around the breech and shoulders.
Use licensed preventive treatments (pour-on insecticides) where strike risk is high.
Select rams with genetic merit for reduced blowfly strike susceptibility in susceptible breeds.
Support research into and adoption of mulesing alternatives that reduce strike without surgical pain.