Materials and Methods
Feeding experiment
The composition of the phase feeding basal diets is given in
Table 1. All diets were changed at the same time. Diets were
based on corn-soybean meal-dried distiller’s grains with solubles
(DDGSs) and were formulated to meet or exceed the nutrient
requirements (National Research Council 1994). All diets were
created from a common basal diet with the only difference being
the amount of vitamin D3 supplemented. The cholecalciferol in
the 5 experimental diets were 2200 (control, or diet 1), 9700
(control + 7500, or diet 2), 17200 (control + 15000, or diet
3), 24700 (control + 22500, or diet 4), and 102200 (control +
100000, or diet 5) IU/kg feed. Experimental diets were generated
every 2 wk to minimize vitamin D3 degradation during storage.
Feed consumption was monitored weekly. Diets were fed to laying
hens (Hy-Line W-36, 19-wk-old) starting at the onset of the
egg laying cycle and continued for the duration of the laying
cycle. Each diet was fed to 3 consecutive pens of 3 hens per
pen (9 birds as one experimental unit) with a total of 8 replicate
groups. Therefore, 72 hens were used for each treatment. Hens
were housed in 68 sq in per birdcage (with stocking density of
438.7 cm2) and arranged in a random complete block design.