Methods for identifying stress caused by fasting in commercial laying hens

Plasma corticosterone concentration (CORT), heterophil:lymphocyte ratio (H:L), catalase activity (CAT), total glutathione concentration (GSH), and thiobarbituric acid reactive substance levels (TBARS) were evaluated in 48 Hy-Line Brown laying hens, at 79 weeks of age, after being fasted for 10 consecutive days. Blood was collected on days zero, two, four, six, eight, and 10 of fasting, and a completely randomized design was adopted, with eight replicates on each day of collection, with each bird being an experimental unit. The time of maximum stress was determined for each method, using the polynomial regression analysis. The Pearson correlation analysis was also performed to determine whether the methods were interchangeable. CORT and GSH concentrations indicated that the time of maximum stress occurred at 4.3 days of fasting, whereas, the H:L and CAT activity indicated that the time of maximum stress occurred at 10 days of fasting. The malondialdehyde concentration detected by the TBARS method was highest at day zero and lowest at day 5.5 of fasting, but this method was not a reliable measure of stress. The low Pearson correlation coefficients observed among the methods made it impossible to designate only one of the tested methods as a replacement for the others, to measure the stress in laying hens during fasting.