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

驱虫药耐药性（AR）是全球可持续畜牧业生产的一个既定障碍，也是英国养牛业的一个新问题。一个广泛提倡的策略，以减缓AR的发展是有针对性的选择性治疗，TST，其中只有一组的共同放牧动物的比例与驱虫剂治疗，允许药物敏感的等位基因在寄生虫种群的保存。在应用TST时，短期生产力和可持续性之间的潜在权衡得到了承认，但没有充分量化，以实现最佳应用。此外，缺乏证据表明TST可有效减缓AR的发展。气候强烈影响TST后线虫的传播，最佳策略可能会在气候变化情景下有所不同。已经开发了模型来预测气候和气候变化对牛的主要寄生线虫物种的自由生活阶段的生态学的影响，并分别由动物科学家评估寄生虫和TST对牛的生长速度的后果。我们建议将这些模型联系在一起，以实现一个综合的，跨学科的模型框架，以了解TST在当前和未来气候条件下选择牛AR的后果，并优化策略以减轻这种选择。由于寄生虫聚集将是这些基于个体的模型的一个紧急属性，TST对聚集的影响，并因此对TST方法，寻求利用聚集的可持续性，将进行探讨。此外，我们将通过在空间和时间上聚集感染阶段来解决气候对寄生虫分布的影响，以及AR遗传学的模型含义，特别是通过稀有等位基因的近亲繁殖和抗性的固定。预测将在英国的养牛场，牛肉和乳制品部门，通过比较预测的增长率和寄生虫分布与使用TST或传统的全组驱虫制度的农场中观察到的情况。验证将扩大到法国西南部，以评估预测的气候变化，特别是干燥的夏季和温和的冬季，将如何影响未来英国条件下的模拟机制。虽然该项目将侧重于将气候、聚集、性能和AR联系起来的基本机制，但这项农场工作还将利用参与性方法，让农民评估影响牛的寄生虫管理的因素，以及如何有效地应用替代战略。最终目标是开发有效的方法来对抗英国牛生产系统中的AR，以持续提高生产力和盈利能力。

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.