Sheep Internal Parasites: Targeted Selective Treatment

Targeted selective treatment (TST) for sheep worms reduces anthelmintic resistance while focusing treatment on animals that most need it for welfare.

Key Facts

Barber pole worm (Haemonchus contortus) is a life-threatening blood-sucking parasite of sheep worldwide
Blanket anthelmintic treatment of entire flocks has driven widespread drug resistance globally
Targeted selective treatment uses FAMACHA scoring, body condition, and fecal egg counts to identify animals needing treatment
TST treats only the 20-30% of animals driving the majority of pasture contamination
Animals with good immune response are left untreated, preserving drug-efficacy refugia in the population
Pasture management and genetic selection for worm resistance complement TST programs

Welfare Considerations

Untreated heavy worm burdens cause anemia, bottlejaw, weakness, and death in sheep. Resistance to all available anthelmintics is an emerging crisis that threatens future ability to treat infected animals. TST balances individual animal welfare (treating those with clinical need) against population welfare (preserving drug efficacy for future treatment). Farmers who adopt TST protect both their animals and the long-term welfare tool of effective worming.

What You Can Do

Work with a vet or animal health adviser to implement FAMACHA scoring on your flock
Send fecal egg samples to a laboratory to assess worm burden and species identification
Select rams with worm resistance estimated breeding values for long-term flock improvement
Avoid buying sheep without checking for anthelmintic resistance status of source flock
Implement pasture rotation to break worm lifecycle and reduce pasture larval burden
Never treat and move sheep - treat, wait 48 hours, then move to clean pasture