Interaction between step-up versus step-down lighting from four to sixteen weeks on growth and development in turkey...

British United Turkeys (BUT) and Nicholas (NIC) hens were exposed to a step-up (10 to 16 h/day) or a step-down (16 to 10 h/day) light program from 4 to 16 wk of age. Lights were increased or decreased by .5h/wk. From 1 to 20 wk, weekly BW data were used to calculate growth curve parameters according to the Gompertz equation. Compared with BUT hens, the slope of the growth curve was greater, but the BW and age at the point of inflection (POI) was decreased in NIC hens. The step-down light program significantly increased the slope of the growth curve, but decreased the BW and age at POI compared with the step-up program. A sample of hens from each strain and program was processed at 16 wk. The relative weight of the Pectoralis minor (P. minor) was increased in BUT hens compared with NIC hens. The absolute and relative weights of the Pectoralis major and the absolute weight of the P. minor were increased in hens from the step-down program compared with the step-up program. The step-up program significantly increased the relative weight of the abdominal fat pad compared with the step-down program, and NIC hens had more abdominal fat than BUT hens. Total carcass lipid was significantly increased by the step-up program, compared with the step-down program, and NIC hens had significantly more carcass lipid than BUT hens.