Growing resistance to antiparasitic drugs in livestock threatens the ability to control internal parasites, creating escalating welfare challenges for affected animals.
Internal parasite resistance causes progressive welfare deterioration: weight loss, anemia, bottle jaw from protein loss, and immune suppression. When the drugs that previously controlled parasite burdens lose effectiveness, welfare problems escalate rapidly. Farms facing multiclass resistance may see significant mortality in susceptible animals before alternative management approaches can be implemented. The transition to refugia-based management and targeted selective treatment requires changing longstanding practices and investing in diagnostic capability, but is essential for preserving welfare-critical treatment efficacy.