Sheep Internal Parasites: Targeted Selective Treatment Welfare Approach

Internal parasites are the leading welfare challenge in sheep production globally. Targeted selective treatment protects both individual sheep welfare and long-term anthelmintic efficacy.

Key Facts

Haemonchus contortus (barber pole worm) causes anemia and death in sheep and is the most welfare-significant parasite
Resistance to all major anthelmintic classes is widespread globally, threatening the long-term capacity to control parasites
Targeted selective treatment (TST) treats only animals with clinical signs rather than blanket whole-flock treatment
FAMACHA scoring of eye color assesses anemia from Haemonchus and guides individual treatment decisions
Refugia - maintaining untreated parasite populations - slows resistance development by maintaining drug-sensitive worms
Breed selection for parasite resistance (including Romney, Merino lines selected for resistance) reduces population-level burden

Welfare Considerations

Internal parasitism causes significant welfare harm through anemia, weakness, bottle jaw from protein loss, and in severe cases death. The welfare challenge of parasite management is that the effectiveness of the treatments protecting sheep welfare today depends on using them wisely to delay resistance development. Blanket treatment of all animals regardless of clinical need accelerates resistance while providing minimal additional welfare benefit over targeted treatment of only affected animals. The welfare-optimizing approach uses FAMACHA and body condition scoring to identify animals needing treatment, maintaining refugia to slow resistance development, and investing in genetic and nutritional strategies that reduce the overall parasite challenge.

What You Can Do

Learn FAMACHA scoring to identify sheep with anemia from barber pole worm requiring treatment
Implement targeted selective treatment protocols that treat clinically affected animals rather than blanket whole-flock dosing
Have fecal egg count reduction tests conducted to confirm anthelmintic efficacy in your specific parasite population
Maintain refugia by leaving 10-20% of the lowest-risk animals untreated to preserve drug-sensitive parasite populations
Consider genetic selection for parasite resistance when making breeding decisions to reduce long-term chemical dependence
Work with a veterinary parasitologist to design an integrated parasite management program for your specific region