Laying performance of challenged and control birds in experiment 1. Eggs were collected throughout the experiment, three times a day, keeping handling of animals to the minimum, in order to avoid the occurrence of stressful events. We compared the egg production between challenged and control birds on a weekly basis, adopting the Wilcoxon matched-pairs signed-ranks on daily mean values for each group. Significance level was set at P < 0.05. Data are shown here as mean ± standard deviations. The differences in the weekly egg production between the two groups were significant (P < 0.05) for 9 weeks after the challenge.