Sheep Parasite Management: Welfare Impacts of Worms and Resistance Strategies

Internal parasites are a leading cause of sheep welfare problems and production loss. Sustainable management requires strategic treatment and genetic resistance selection.

Key Facts

Gastrointestinal nematodes, particularly Haemonchus contortus, cause anaemia, diarrhoea and death in sheep.
Anthelmintic resistance is now widespread globally, reducing the effectiveness of chemical treatments.
Infected sheep show reduced growth rates, wool quality and reproductive performance.
FAMACHA scoring — assessing eye membrane colour — allows targeted treatment of most-affected individuals.
Grazing management including pasture rotation reduces larval contamination and worm burden.
Selective breeding for parasite resistance offers a long-term sustainable solution to the resistance crisis.

Welfare Considerations

Parasite burden causes chronic suffering in affected sheep including lethargy, weakness and weight loss. Severe infections lead to anaemia and death if untreated. The growing crisis of anthelmintic resistance makes blanket treatment approaches unsustainable and ineffective, requiring more sophisticated welfare-aware management. Targeted selective treatment guided by clinical indicators, combined with grazing rotation and resistance breeding, represents the evidence-based approach. Farmers who adopt integrated parasite management reduce animal suffering while also protecting the long-term efficacy of available medicines.

What You Can Do

Support research into sheep genetic resistance to parasites and alternative control methods.
Advocate for integrated parasite management training in agricultural extension programmes.
Choose lamb from producers using welfare-sensitive parasite management practices.
Learn about the anthelmintic resistance crisis and its animal welfare implications.
Encourage vets to promote targeted treatment rather than blanket dosing protocols.