Small ruminants, especially sheep, are well-suited to grazing systems. Grassland, however, is also well suited to support the life cycle of nematodes and other parasites that are transmitted from the faeces and ingested from the surrounding grass. The more systems rely on grazing, the greater the risk from these parasites. A wide range of parasites can infect sheep, including protozoa, helminths and arthropods (Pomroy, 2017). It has been estimated that gastrointestinal parasites may cost the UK sheep industry alone approximately £50 million annually in mortality, lost production and veterinary costs, with estimates of the cost to the EU sheep meat sector varying between €130 million and €250 million (Charlier et al., 2020; Reeves et al., 2024). Perhaps the most important group of parasites is gastrointestinal nematodes (GINs) that are known to affect both intensive and extensive systems of sheep production (Mavrot et al., 2015; Pomroy, 2017; Geddes et al., 2024).