Figure 2.

BW of pullets in dark and light groups from week 0 to week 18 of White Leghorn (A), Rhode Island Red (B), Columbia Rock (C) and Barred Rock (D). Data are presented as mean ± SEM (2 replicates of each group at each week of age). Asterisk indicates significant difference between groups at a given specific week (∗P < 0.05, ∗∗P < 0.01). Abbreviations: dark group, 0L:24D; light group, 12L:12D.