TY - JOUR AU - Lerner, I. Michael TI - Poultry breeding: Long-term selection studies aim at breaking through the ceiling limiting further improvement of economic traits JF - California Agriculture JO - Calif Agr Y1 - 1951/11/01 VL - 5 IS - 11 SP - 15 EP - 15 PB - University of California Agriculture and Nature Resources SN - 0008-0845 UR - http://www.ucanr.edu/sites/calagjournal/archive/?article=ca.v005n11p15 AB - Most breeders of chickens who start with average or below-average commercial flocks have little difficulty in obtaining improvement by selection of economic characters.