Under conditions of shared grazing, owners must realise that if their horse is shedding lots of worm eggs, other horses in the paddock are likely to become infected The paddocks available for grazing may be smaller than is ideal for the number of horses. This may lead to close-cropped grass and horses grazing close to piles of dung where there are higher numbers of infective larvae Most livery yards have a high turnover rate of horses problem which causes added problems from a worming perspective New horses, with unknown worming histories, are a potential threat. They might bring worms into a clean population of horses and they might introduce resistant strains of small redworms Diagnostic tests (faecal worm egg counts and tapeworm antibody tests) can help assess the parasite status of new horses so they can be treated appropriately before mixing with others All horses should have faecal egg counts performed prior to dosing Treatment is then targeted at animals with adult parasites (as indicated by a worm egg count of more than 200 eggs/gram ) Eggs counts are a useful indicator but do not correlate well with the total parasite burdens Egg counts will not identify the presence of immature or encysted small redworm larvae within the gut wall (mucosal stages), so egg counts are best performed in the Summer months when mucosal numbers are likely to be lowest.