Index to identify Gastrointestinal Nematodes Resistance in Sheep

Chew, Woon Ling (Victoria)
Federation University


Gastrointestinal nematodes (GIN) present welfare and economic risks to producers. Control is primarily anthelmintics, though other methods such as genetic breeding are viable. Using Australian Sheep Breeding Values (ASBV), worm egg count (WEC) can be used to breed for less susceptible sheep. Despite control efforts, GIN still present significant economic and health impacts. To enhance flock management and selection for breeding purposes, biomarkers tested experimentally could be utilised. The study aims to build on this work by expanding markers of GIN infections on a commercial farm. Thirty GIN Resistant (n=15) and Susceptible sheep (n=15) were selected from Curlew Merinos based on ASBV for yearling WEC. Blood, faecal, saliva samples and live weight were collected on Days 1 (Week 1) and 28 (Week 4) to determine parasitological (WEC), immunological (IgA, eosinophilia) and physiological (pepsinogenaemia, weight gain) parameters. Generalized linear mixed modelling was used to determine relationships between collected parameters during a natural GIN infection; then, an index comprising of all markers of worm resistance was created to rank the animals. Susceptible sheep weighed heavier although Resistant animals tended to have higher blood eosinophil count (p=0.1262). Cost of immunity was suggested, as animals with higher immune activity had production trade-offs. It is possible to select animals based on indices of GIN resistance but more work needs to be done in this area.