This project will slow the development of anthelmintic resistance (AR) in UK sheep flocks by developing and promoting evidence-based strategies for sustainable treatment of ewes at lambing time. Guidelines for the sustainable control of parasites in ewes (SCOPE) will be developed by quantifying the production and epidemiological impacts of periparturient ewe treatments and simulating selection for anthelmintic resistance under a range of flock management strategies and climatic conditions, using gastrointestinal nematode (GIN) epidemiological models that I have already developed. The project addresses a STAR-IDAZ International Research Consortium in Animal Health's priority research topic and several key challenges. By providing farmers with information and guidance to help them minimise inputs whilst at the same time upholding high standards of welfare and productivity, the project also aligns with Defra's Animal Health and Welfare Pathway. Helminth infections are a major economic and welfare burden to UK ruminant production enterprises, costing the UK sheep industry an estimated £41m per year. Parasitic gastroenteritis and anthelmintic resistance (AR) are now considered by UK industry professionals to be the second most important sheep disease and syndrome in the UK. GIN infections in periparturient ewes are of particular concern due to the direct effects of infection on lamb exposure to infection. Most UK farmers treat periparturient ewes with moxidectin, yet treating ewes at lambing time has the potential to select heavily for AR. Despite this risk, the epidemiological and evolutionary impacts of anthelmintic treatment of periparturient ewes on GIN populations have not yet been robustly quantified. To date, no controlled, randomised study investigating the impact of ewe treatments on AR has been conducted in the UK, nor in Europe, and no studies of this nature have investigated the use of moxidectin. The overarching aim of this project is to provide an evidence base for industry guidelines for the sustainable use of anthelmintics to control GIN in ewes, which promote high levels of welfare and productivity, yet slow the development of AR. We will achieve this with three specific objectives which combine empirical parasitology, population genetic analyses and mathematical modelling. 1. Quantify the consequences of ewe treatments for GIN epidemiology, AR, GIN population diversity, and lamb productivity 2. Develop and validate a mathematical model to simulate the development of AR following anthelmintic treatment of ewes 3. Simulate the outcome of treatment strategies for controlling the PPR-FEC in ewes throughout the UK, and determine the most sustainable regional approaches We will work closely with industry stakeholders throughout, including project partners, to develop guidelines/recommendations for the sustainable anthelmintic control of parasites in ewes. These will be disseminated through partners and at industry events, and the impact of our research will be evaluated through farmer surveys of behaviour change. The outcomes of this research will feed directly in to updated nationwide industry guidelines for the sustainable control of parasites in ewes.