Resistance v resilience: Losing the battle, what about the war?

Content Partner: Lincoln University. Selection of animals that are genetically either resistant or resilient to gastro-intestinal nematodes (GIN) are two divergent approaches for sustainable parasite control. Resistant animals will excrete fewer eggs on pasture likely leading to an epidemiological benefit (Bisset et al., 1991). Extrapolation of the relationship between larval challenge and animal performance (Coop et al., 1982) then leads to the conclusion that increases in performance will ensue (Bishop, Stear, 1997). However, this assumes the physiology of animals selected for resistance is unchanged, which may not necessarily be the case (Greer, Hamie, 2016). Previous studies investigating the production differences between lines of animals selected for resistance or resilience have reported greater levels of productivity in resilient animals (de Lautour, de Lautour, 2010; Bisset et al. 1997; Morris et al., 1997). Comparisons which have been made where lambs of each phenotype are grazed together and may have resulted in underestimation of the impact of host genotype due to potential masking effects. In the present study, the epidemiological and animal performance lines of Romney sheep selecting for either resilience or resistance to GIN parasites was evaluated grazed either separately and or mixed in farmlets.