Barber Pole Worm in Sheep and Goats: A Lethal Internal Parasite Crisis

Haemonchus contortus, the barber pole worm, is a blood-sucking gastrointestinal nematode that kills thousands of sheep and goats annually, causes significant suffering through anaemia and weakness, and is increasingly resistant to the anthelmintic drugs used to control it.

Key Facts

Haemonchus contortus is a blood-sucking worm inhabiting the abomasum — each worm consumes up to 0.05 mL of blood per day
Heavy infections in a single sheep can involve thousands of worms consuming significant proportions of the animal's blood volume daily
Affected animals develop severe anaemia, weakness, bottle jaw (fluid accumulation under the jaw), and can die rapidly
Lambs and young stock, pregnant ewes, and animals under nutritional stress are most vulnerable to severe disease
Resistance to all major anthelmintic classes (benzimidazoles, macrocyclic lactones, levamisole) is widespread and growing globally
The FAMACHA eye scoring system assesses anaemia by conjunctiva color, allowing targeted treatment of the most severely affected animals only
Refugia-based approaches — leaving some animals untreated to maintain susceptible worm populations — are critical for slowing resistance development

Welfare Considerations

Barber pole worm causes genuine suffering that can be rapid and severe. An animal with a heavy burden is experiencing blood loss equivalent to repeated phlebotomy, causing weakness, inability to graze effectively, and progressive organ failure from anaemia. Death in severe cases can occur within days of clinical signs appearing. The welfare tragedy is compounded by the anthelmintic resistance crisis — drugs that once controlled barber pole worm effectively are losing efficacy, leaving producers with limited treatment options. Resistance is largely a consequence of historical overtreatment, which selected strongly for resistant worm populations. Sustainable parasite management that preserves drug efficacy while minimizing animal suffering requires careful monitoring, targeted treatment, and breed selection for natural parasite resistance.

What You Can Do

Work with a veterinary parasitologist to develop a FAMACHA-based targeted treatment program that treats only animals that genuinely need it
Use fecal egg counts to monitor worm burdens and guide treatment timing rather than calendar-based whole-flock treatments
Select for parasite resistance through breeding programs using estimated breeding values for fecal egg count where available
Maintain refugia by never treating the entire flock simultaneously — leave untreated animals to dilute resistant worm populations on pasture
Rotate pastures to reduce larval contamination and give previously grazed paddocks rest periods
Consult your vet promptly when animals show FAMACHA scores indicating anaemia — delayed treatment causes significant unnecessary suffering