Internal parasites are a major welfare challenge in sheep, and the growing problem of anthelmintic resistance requires strategic management to protect both animal welfare and treatment efficacy.
Gastrointestinal parasitism causes significant welfare harm including anaemia, bottle jaw, diarrhea, weight loss, and death in severe cases. The welfare-optimal strategy balances effective parasite control against preservation of anthelmintic efficacy for future generations. Blanket treatment of all animals without regard to parasite burden is both a welfare and resistance risk. Targeted selective treatment based on FAMACHA scoring, clinical signs, and faecal egg counts treats animals in need while maintaining refugia. Quarantine treatment of introduced animals prevents importation of resistant worms. The collapse of effective anthelmintics through resistance would represent a catastrophic welfare outcome for the sheep industry.