Breeding sheep for genetic resistance to gastrointestinal parasites offers a sustainable, welfare-positive alternative to reliance on anthelmintics, which are losing efficacy due to widespread resistance.
Breeding sheep for parasite resistance represents one of the most promising intersections of animal welfare and sustainable agriculture. Heavy worm burdens cause profound welfare compromise: anaemia from blood-sucking nematodes causes weakness and lethargy; protein loss impairs growth and reproduction; in severe cases, affected sheep become recumbent and die. The welfare impact is insidious because early clinical signs — subtle loss of condition and vitality — are easy to miss. As anthelmintic resistance grows, the options for conventional treatment narrow, making the genetic route increasingly important. Selecting rams with favourable estimated breeding values (EBVs) for parasite resistance, combined with targeted selective treatment based on individual animal assessment (FAMACHA scoring), reduces the welfare burden of parasitism while slowing the development of resistance. This approach benefits both the individual animal and the long-term productivity of the flock.