Resistance to antiparasitic drugs threatens both livestock welfare and the ability to treat parasitic disease, requiring new management approaches.
Anthelmintic resistance is a slow-motion welfare crisis. As resistance spreads, the drugs that have provided reliable protection against parasitic worms become less effective - animals suffer parasitic disease that was previously controllable. The welfare consequences include anemia, protein loss, diarrhea and death in heavily parasitized animals. Critically, the resistance problem was largely created by the practices intended to prevent welfare harm - routine preventive treatment of all animals on fixed schedules selected strongly for resistant worms. Targeted selective treatment, though requiring more monitoring effort, slows resistance development while maintaining equivalent or better individual animal welfare. Preserving the efficacy of existing drugs through resistance management is itself a profound welfare intervention.