The effect of light regimen, floor space, and energy and protein levels during the growing period on body weight and early egg size.

Two experiments (Exp.) were conducted to determine whether dietary manipulation of energy and protein, additional floor space, and the use of a step-down light regimen during the growing period can influence BW of the White Leghorn pullets at the age of housing (18 wk) and egg size during the early stages of egg production. The results of Exp. 1 indicated that BW at 18 wk of age was increased (P < 0.05) due to the use of high energy (3,036 vs 2,816 kcal ME/kg) or high protein (17.5 vs 14.5%) diets or providing the pullets with more floor space (346 vs 283 cm2 per pullet) from 8 to 18 wk of age. However, the extent of increases of BW due to these variables were not large enough to increase egg size during the early stages of the egg production cycle. The results of Exp. 2 indicated that 18-wk BW was increased (P < 0.05) only due to the use of a high protein sequence (22, 18, and 16% vs 18, 16, and 14% that were used during 0 to 6, 6 to 12, and 12 to 18 wk of age, respectively). Body weight at 18 wk of age was not influenced by the use of a higher energy diet (3,036 vs 2,816 kcal ME/kg) from day-old to 18 wk. Energy or protein levels did not have an effect on early egg size or overall performance up to 66 wk of age. Body weight of the pullets on the step-down light regimen (which were exposed to 23 h/d light at day-old and was gradually reduced to 8 h/d at 15 wk of age) were heavier than the pullets of the short-day light regimen (which were exposed to 8 h/d light during the growing period) during most parts of the growing and laying periods (P < 0.05). The step-down light regimen resulted in increased egg size and higher percentage of extra-large plus large-sized eggs for the entire experiment (P < 0.05), but reduced hen-day egg production and egg mass and impaired feed conversion (P < 0.05) for the entire experiment (18 to 66 wk of age).