Gastrointestinal parasites, particularly Haemonchus contortus, are a leading cause of morbidity and mortality in sheep worldwide, causing significant welfare harm and economic loss.
Gastrointestinal parasitism is one of the most pervasive welfare problems in sheep production globally. Heavily infected sheep experience progressive anemia, weakness, and weight loss over weeks — a welfare deterioration that occurs slowly and may not be apparent until animals are severely compromised. The anthelmintic resistance crisis means that old treatment protocols are increasingly ineffective, requiring more sophisticated management approaches that many small farmers lack training to implement. The welfare and economic costs of this problem are inseparable — sick sheep grow poorly — yet resistance management requires short-term restraint in treatment that runs counter to conventional farmer behavior.