Internal parasites including Ostertagia and liver fluke cause significant welfare impairment in beef and dairy cattle, with anthelmintic resistance making strategic targeted treatment essential for both animal welfare and drug efficacy preservation.
Internal parasite welfare impacts are chronic and insidious: subclinical infections reduce growth rates, impair immune function, and cause low-grade malaise that may never trigger obvious clinical signs. Acute fasciolosis causes severe abdominal pain and rapid deterioration in heavily infected animals. The anthelmintic resistance crisis is a welfare threat as well as a productivity concern - resistance renders treatment ineffective, leaving animals without adequate parasite control. Welfare-centered parasite management balances individual animal treatment needs (identified through evidence-based monitoring) against resistance preservation to maintain effective treatment options for future generations of animals.