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Improving host genetics for resistance to parasites: searching for optimum
phenotypes in a changing climate
Eric R. Morgan* and Hannah Rose
University of Bristol, School of Veterinary Science, Bristol Life Sciences Building, 24,
Tyndall Avenue, Bristol, BS8 1TQ, United Kingdom
*Corresponding author: [email protected]; Tel. +44 1173 941195
ABSTRACT
The long tradition of selective breeding of domestic animals for resilience to parasite
infection has accelerated with intensifying threats such as drug resistance, and as new
statistical and molecular tools become available. Progress has been best documented for
resistance to gastrointestinal nematodes in sheep, with resistance traits being integrated into
breeding programmes in the field, and significant efforts directed to enhanced detection of
resistant genotypes. Several areas of debate have emerged, including the relative place of
resistance and tolerance in parasite resilience and its economic benefits, and the potential for
selective treatment approaches to underpin alternative pathways to genetic improvement.
Notably, selection under current parasite challenge could be undermined by altered parasite
epidemiology in future, especially as a result of climate change. We present results from
predictive models of nematode free-living stages that compare the epidemiological benefits
of reduced faecal worm egg output under different climatic and management scenarios. This
approach could help to design optimal phenotypes for future farms, and hence inform
breeding programmes through prioritisation of traits and markers. At the same time,
increasing emphasis on refugia-based treatment strategies provide opportunities for farmerled selection for parasite resilience, especially where more centrally developed genetic
resources are unavailable. Efforts to develop host resistance or resilience in other hostparasite systems could benefit from similar strategic consideration of the potential impacts of
climate change on epidemiology. Ultimately, breeding programmes for different parasitic and
other diseases should be integrated so that their aims align in the best interests of sustainable
livestock farming.