Data from three generations of two brown purebred lines of a commercial breeding programme were analysed. The total testing period range from 20 to 60 weeks of age (ENT) was subdivided into ten four week periods (EN1 to EN10) to study genetic progress of egg production in part-periods. Genetic analysis showed that despite apparent decreasing rates of genetic progress in total egg production a selection plateau has not been reached. Trait EN1 showed relatively high heritabilities (h(EN1)(2) = 0.22-0.39) and was influenced by sexual maturity. Thereafter peak rate was characterized by low phenotypic and genetic variances (h(EN2)(2) = 0.04-0.19; h(EN3)(2)=0.02-0.15; h(EN4)(2)=0.10-0.18). Genetic correlations between early part record and total egg number (ENT) were variated (r(g)=-0.23 to 0.73). With increasing production stage, heritabilities increased. Moderate to very high correlations were estimated between late periods and total egg number (ENT) (r=0.64-0.94). Investigations in order to optimize selection time showed higher improvement when total performance of parental generation was included in breeding value estimation. Selection on cumulative laying rate to week 44 including total performance of parents was up to 20% more efficient than selection on total egg number of current generation.