The pullets' rate of body weight gain can be controlled, in part, by the lighting program. Moreover, the rate of body weight gain is influenced by nutrition, the number and timing of beak treatments, the vaccination program, and the overall health status of the pullets. Birds grown on the floor will expend more energy and will often be as much as 50 g (0.1 lb) lower in body weight at 12 weeks of age than cage-grown birds. To offset any decrease in egg size caused by low body weights, it is common to delay light stimulation until the pullets reach the breed's stimulation body weight (usually the 18- week target weight).