The weight of lamb carcass produced per hectare is one of the major factors influencing the efficiency of lamb production and is influenced by the litter size and subsequent lamb growth rate (Keady and Hanrahan, 2006). On many sheep farms ewes are housed during the winter to facilitate increased stock carrying capacity. Ewes are normally shorn once yearly, usually in early summer. Previous studies at Athenry (Keady et al., 2007, Keady and Hanrahan, 2008, 2009) have shown that shearing ewes at housing increased subsequent lamb birth and weaning weights by up to 0.6 and 2.5 kg, respectively. Therefore as a consequence of reducing age at slaughter by approximately 2 weeks, whilst increasing price received per kg of carcass. However, shearing at housing may increase management inputs as ewes are normally housed in smaller groups and need to be dry prior to shearing. Shearing in the autumn, prior to mating, enables the flock to be assembled under more favourable conditions. A previous study at this centre (Keady and Hanrahan, 2008) showed that shearing prior to mating tended to increase subsequent lamb birth weight (+0.3 kg) but did not alter litter size or lamb viability relative to lambs born from ewes which were shorn in late May. The aim of this study was to further evaluate the effects of season of shearing on fertility of March -lambing ewes and on subsequent lamb performance.