For this purpose,
40000 day-old broiler chickens were placed in four houses as follow: green, sunny yellow, blue
and red light. All light sources were equalized at the intensity of 25 lux, with light period of 23
hours daily. In days 8, 18, 30 and 42 from each house, 25 samples of serum were obtained to
evaluate the ND-antibody responses.