After a one-week adaptation period to cages(70 cm length x 30 cm width x 40 cm height), the birds were allocated to 4 groups with 6 replicates of 18 birds (6 adjacent cages, 3 birds per cage) each. No difference (P>0.05) was observed on the egg production and egg weight between the 4 groups before the experiment (day 0). The replications were allotted equally into the upper and lower cages to minimize the effects of cage level. The cages were equipped with nipple drinker and trough feeders, and hens were housed in a windowless laying house at approximately 21 ํC