Growth and development of lines of Japanese quail (Coturnix coturnix japonica) divergently selected for body weight at 4 weeks of age.

1. Divergent selection for body weight resulted in significant increases and decreases in body weight and the relative weight of the pectoralis major breast muscle in heavy (HW) and light weight (LW) strains of Japanese quail compared with a randombred control strain (R1). 2. The relative weights of the abdominal fat pad and total carcass lipid were increased in the HW strain, particularly in the females. 3. Sexual maturity was similar in HW and R1 hens but was delayed in the LW hens. HW hens laid significantly more double-yolked eggs.