Previous studies (Keady et al., 2007; Keady & Hanrahan, 2007) at Athenry have shown that shearing ewes at housing increases subsequent lamb birth and weaning weights. Keady et al., (2007) reported that shearing at housing increased gestation length whilst Keady and Hanrahan (2007) reported that shearing increased food intake, both indicative of reduced heat stress. The temporary loss of acquired immunity to gastrointestinal nematodes that is associated with an increased faecal egg output in late pregnancy and early lactation, is a well established phenomenon and is important in the epidemiology of nematode parasites of sheep. Given the association between nutrition (Donaldson et al., 1997; 1998; Coop and Kyriazakis, 1999; Houdijk et al., 2000) and the periparturient rise in nematode eggs (PPR) in ewes, the increased food intake evoked by shearing at housing, may have an impact on the PPR. The aim of this study was to evaluate the effect of season of shearing on the periparturient rise in nematode egg output in ewes.