Genetic improvement in production of commercial layers was examined by comparing production profiles of three strains representing commercial stocks of the two decades between 1950 and 1970, and by considering North American random sample tests for several production traits performed during the period 1970–80 with stocks that are used commercially in temperate climates around the world. Changes in the production profiles indicate commencement of production at an earlier age and increased persistency of egg production after reaching the peak level. Results from the North American random sample tests of multiple trait selected stocks show improvements not only in egg production, but also in egg size, while egg quality and viability have been maintained.
