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

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.

We propose to leverage recent advances in the predictive biology of nematode infection dynamics within and outside cattle to determine optimal strategies for targeted selective treatment (TST) application in current and future conditions. This requires the introduction of stochasticity in simulation models, to identify individuals that would benefit from TST and quantify its consequences. Because TST relies on aggregation of parasites, such that a few individuals within a herd carry most of the parasite population, we will also examine the way in which aggregation changes under different TST regimes, and how this interacts with climate. Spatial aggregation of infective stages, a key driver of parasite aggregation in grazing ruminants, arises from moisture-dependent larval migration from dung pats, and favours inbreeding and the fixation of rare resistance alleles in the early stages of AR development. Therefore, we further propose to investigate effects of climate on the spatial and temporal distribution of infective larvae at pasture using laboratory experiments and field trials in the UK and in southern France. Results will integrate new understanding of larval ecology with animal science to predict how aggregation and TST affect each other, and develop robust recommendations for the optimal application of TST in UK cattle. Outcomes will be more efficient and sustainable control of parasites in cattle to support enhanced productivity, and a predictive framework for dynamic interactions between control and parasite populations on livestock farms.

The proposal involves collaboration and co-production with key stakeholders from the UK and global Industries that aim to enhance the sustainability of grazing ruminant systems by dealing with the challenge of anthelmintic resistance (AR). We will use new insights about the sustainability of current practices to control, and state of the art approaches to reduce the development of AR by nematode parasites. Although the proposal focuses on cattle the outputs of the project are likely to be applicable to other Industries that deal with grazing livestock.

Specifically, we will develop a Decision Support Tool (DST) with Industry stakeholders and adapt it to suit their needs for the development of targeted selective treatment (TST). The DST will be tested with key stakeholders. The long-term aim is to generate a resource that can be updated from rapidly generated information on AR, so that its parameters and inputs can be updated regularly and provide alternative options for the relevant Industry, in response to system driver changes.

In addition, we will use outputs from the stakeholder analysis to identify activities as part of a detailed post-award impact strategy for the project. In addition to identifying Industry Stakeholders for participatory scenario development, this systematic approach will enable the project to create a Project Stakeholder Group (PSG) to represent the interests and voices of all key groups interested in the work. The role of PSG will be to: i) ensure project goals are consistent with the needs of beneficiaries; ii) review and provide feedback on project progress towards stated goals; iii) develop indicators with the project team to ensure that research impacts can be tracked effectively.

We envisage using stakeholder engagement pathways to impact, with a range of activities developed specifically to appeal to and benefit different stakeholders, based on evidence from the stakeholder analysis. Such activities will be co-designed with the PSG, but indicative activities are set out in the Pathways to Impact document.