Sheep Internal Parasite Management and Welfare

Gastrointestinal nematode parasites are the most significant welfare and production challenge in sheep farming, requiring targeted rather than blanket treatment to manage effectively and sustainably.

Key Facts

Haemonchus contortus (barber pole worm) causes potentially fatal blood loss in sheep, particularly young animals and ewes
Benzimidazole, levamisole, and macrocyclic lactone resistance is widespread in nematode populations globally
FAMACHA eye scoring assesses conjunctival color as a proxy for anemia, enabling targeted treatment of high-burden animals
Refugia management preserving susceptible worms in untreated animals slows resistance development
Genetic selection for worm resistance enables long-term flock improvement without reliance on anthelmintics
Pasture management including rest periods and mixed-species grazing reduces infective larval burden

Welfare Considerations

Internal parasites cause significant welfare compromise through anemia, bottle jaw, scouring, and failure to thrive in affected sheep. Haemonchus causes rapid deterioration and death in young lambs during spring and summer flush conditions. Anthelmintic resistance makes effective parasite control increasingly difficult, threatening the welfare of flocks that relied on blanket treatment. Targeted treatment approaches enabled by FAMACHA scoring reduce treatment burden while maintaining welfare in highly parasitized individuals. The complexity of sustainable parasite management requires producer education and often specialist veterinary guidance.

What You Can Do

Learn FAMACHA scoring and use it for targeted treatment decisions rather than blanket treatment
Work with your vet to conduct fecal egg count reduction tests to assess anthelmintic efficacy on your farm
Practice refugia management by leaving the lowest-burden animals untreated to preserve susceptible worm populations
Consider genetic selection for parasite resistance when purchasing rams to improve flock resilience
Monitor body condition and growth rates as early indicators of subclinical parasitism in young stock