**SCOPS INTERNAL PARASITE TECHNICAL MANUAL** This is an update of the SCOPS Internal Parasite Technical Manual for Vets and Advisers, following an expert review during 2019/20. In this new format, all sections can be accessed using the navigation tree, and these include links to additional documents. Sections will be updated as necessary, and flagged, to enable you to keep abreast of developments in SCOPS science and practice. For the details of latest updates please [click here][1]. For the details of the authors and acknowledgements please [click here][2]. **CONTENTS** **What is AR?** Anthelmintic resistance (AR) is the heritable ability of the parasite to tolerate a normally effective dose of an anthelmintic. The parasite is considered resistant if it survives exposure to the standard recommended dose of the anthelmintic and the ability to survive is passed on to its offspring. **SCOPS Principles** The SCOPS principles are designed to help slow the development on sheep farms. They are based on three main drivers for resistance: 1. The frequency of anthelmintic use on a farm - every treatment selects for any resistant parasites present in the animal. 2. The efficacy of each treatment – the accuracy of the dose and application, together with the level of resistance present to that product. 3. The proportion of the total worm population in the animal at the time of treatment and how quickly any surviving parasites are diluted with unselected parasites in refugia of each treatment. **Internal Parasites & Diseases** Disease caused by gastrointestinal nematodes may be acute in onset, with clinical disease, including some mortality, affecting >10% of a flock. However, these parasites also cause sub-clinical disease, with reduced growth rates, milk and wool production and body condition which result in significant financial loss to the industry. The pathogenicity and severity of the various GI parasites are outlined in this section, together with detail on the development of immunity to internal parasites and how this is an important factor in the reduction in our reliance on anthelmintics. **Anthelmintics** Anthelmintics remain an important part of effective worm control in sheep. In order to protect their long term efficacy it is vital we ensure the right product is used and it is applied accurately. Failure to make the right initial choice together with inadvertent selection pressure on parasites when a combination is used unnecessarily are important sources of over-use. In this section the various options including broad and narrow spectrum products are described to help prescribers. A full list of all sheep anthelmintics available by product name can be found [Here][3] **ACKNOWLEDGEMENTS** Editor: Lesley Stubbings, LSSC Ltd. The content of the manual was reviewed in 2019 and SCOPS are very grateful to VMD (Veterinary Medicines Directorate) who helped to support the writing of updates, and Elanco, Zoetis and Boehringer Ingelheim AH for facilitating a workshop. The content within this ‘tree’ on the SCOPS website replaces the Technical Manual (Abbott, Taylor and Stubbings, 2012). Authors of various sections are as follows: - Dr Dave Bartley, Moredun Research Institute, Dave.Bartley@moredun.ac.uk - Dr Valentina Busin, University of Glasgow, Valentina.Busin@glasgow.ac.uk - Dr Fiona Lovatt and Phillipa Page, Flock Health Ltd., office@flockhealth.co.uk - Dr Hannah Rose Vineer, University of Liverpool, Hannah.Vineer@liverpool.ac.uk - Dr Phil. Skuce, Moredun Research Institute, Philip.Skuce@moredun.ac.uk - Lesley Stubbings, LSSC Ltd., lesley@lssc-ltd.co.uk [1]: https://www.scops.org.uk/advisers-technical-info/updates/ [2]: https://www.scops.org.uk/advisers-technical-info/authors/ [3]: https://www.scops.org.uk/workspace/pdfs/anthelmintics-scops-lssc-web-version-2020.pdf