We are studying the problem of parasitic gastroenteritis (gut worms) in sheep. We hope to aid UK farmers to farm more efficiently and have less environmental impact. In world where many wormer classes are not working sufficiently, we need to explore the growth rates and financial rewards that can be achieved by exploiting the genetic that can give sheep tolerance or resistance to worms. A study of 45 farms in the South West (1) recently found that around 94% of the average Farm Business Income was made up of the Basic Payment Scheme, which soon to be withdrawn. Anything we can be doing to farm more efficiently should therefore be considered. We run a farm in Cornwall with 800 breeding ewes and regularly pull genetics from the New Zealand flock by importing Rams. We hope to identify and exploit the genetic variation in some sheep which allows them to tolerate or be resistant to worms, whilst still growing sufficiently. Exploiting tolerance or resistance to worms could result in reducing farm labour for drenching, lowering treatment frequency and costs, increasing lamb growing efficiency whilst also improving sheep welfare and production. To test and identify tolerance or resistance, approximately 200 of the Trefrank Farm ram lamb crop (2022) will be weighed and have dung samples taken for faecal egg testing every 2 weeks from July - November. We aim to identify those lambs that can tolerate a high gastrointestinal worm burden whilst still maintaining adequate growth rates. A control group of 20 lambs will be wormed every 4 weeks to act as a 'control' by which to benchmark the test groups' growth rates. It is crucial that welfare is constantly assessed as measured by performance, and any test lambs dropping below 70% of the control group's growth rates will be drenched with a wormer. Results will be analyzed by scientists at the Moredun Institute and disseminated through CIEL. Alongside informing farmers practically, this study will increase the evidence-based knowledge for vets, researchers and also farmers. This approach to using genetics could potentially be replicated and also encourage others to consider tolerance as an important factor in a productive, welfare-driven flock. 1. 'North Devon Pioneer Project' - Business Information Point, Devon