Integrating ecology and animal science to understand and manage anthelmintic resistance in cattle under climate change

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Anthelmintic resistance (AR) is an established barrier to sustainable livestock production globally, and is an emerging issue for the cattle farming industry in the UK. A widely advocated strategy to slow the development of AR is targeted selective treatment, TST, whereby only a proportion of a group of co-grazing animals are treated with anthelmintic, allowing preservation of drug-susceptible alleles in the parasite population. The potential trade-offs between productivity in the short term and sustainability when applying TST are acknowledged, but not sufficiently quantified to enable optimal application. Moreover, evidence to show that TST is effective in slowing the development of AR is lacking. Climate strongly affects onward transmission of nematodes following TST, and optimal strategies are likely to differ under climate change scenarios. Models have been developed to predict effects of climate and climate change on the ecology of the free-living stages of major parasitic nematode species of cattle, and separately by animal scientists to evaluate the consequences of parasites and TST on growth rates in cattle. We propose to link these models together to achieve an integrated, interdisciplinary model framework to understand the consequences of TST for selection of AR in cattle under current and future climates, and so optimise strategies to alleviate this selection. Since parasite aggregation will be an emergent property of these individual-based models, the effect of TST on aggregation and thence on the sustainability of TST methods that seek to leverage aggregation, will be explored. Further, we will address the effect of climate on parasite distribution through aggregation of infective stages in space and time, and model implications for the genetics of AR, specifically through inbreeding of rare alleles and fixation of resistance.Predictions will be validated on cattle farms in the UK, in beef and dairy sectors, by comparing predicted growth rates and parasite distributions with those observed on farms that are using TST or conventional, whole-group deworming regimes. Validation will be expanded to south-west France, to assess how projected climate change, especially drier summers and milder winters, will affect the modelled mechanisms under future UK conditions. Although the project will focus on fundamental mechanisms linking climate, aggregation, performance and AR, this on-farm work will also utilise participatory approaches to farmers' assessments of the factors affecting parasite management of cattle and how alternative strategies might be effectively applied. The ultimate aim is to develop effective, efficient ways to combat AR in cattle production systems in the UK, for sustainable improvements in productivity and profitability.