Impacts of selecting sheep for resistance and resilience to gastro-intestinal nematode parasites : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Content Partner: Lincoln University. This study investigated the impacts of decades of divergent selection for either resistance or resilience to gastrointestinal nematode (GIN) parasite infection in Romney sheep lines and involved a series of three studies. Study 1 (Chapter 3), assessed the variation in timing of development of immunity and physiological maturity in Romney selection lines; one selected for resistance and the other selected for resilience when exposed to natural mixed-species GIN parasite infection with no anthelmintic treatment. From weaning at mean 92 days-of-age, animals (n=53) were sampled for faecal egg count (FEC) expressed as eggs per gram of faeces (epg), saliva for immunoglobulin (IgG and IgA) determination and fasted live weight (LW) every 10 days until 351 days-of-age. Overall, mean back-transformed FEC were consistently low for resistant animals (