Nutrition of the ewe during early pregnancy has important implications for lamb output through its effects on implantation and early embryonic development. In adolescent ewes a high plane of nutrition during the first half of gestation has been found to reduce conception rate, lamb birth weight and neonatal lamb survival (Wallace et al., 1996). However few studies have examined the effects of nutrition immediately post-mating on foetal development and subsequent lamb performance. The current experiment was set up to investigate how plane of nutrition of adolescent and mature ewes during the first month after mating affects lamb output, foetal development and lamb growth.