Laying hen behavior 2. Cage type preference and heterophil to lymphocyte ratios

Studies were conducted to determine hen preference for and stress response to cage type. By using a plywood (1.25 cm) test apparatus with open- and solid-sided compartments and a plexiglass divider at the entrance for controlling passage, birds (n = 20) were evaluated as to their choice of compartment after training and acclimation. For each test, after training, an individual bird was placed in the start box and given 1 min to acclimate before making a choice. The experiment was repeated after rotating the apparatus 180 degrees. In Experiment 1, the open-sided compartment was chosen by 45% of the hens, and the solid-sided compartment by 25% (P = 0.02); 30% chose neither. In Experiment 2, the compartment with open sides was chosen by 70% of the hens, and that with solid sides was chosen by 15% (P = 0.004); 15% chose neither. The length of time required to choose one compartment over the other did not differ in either experiment (P = 0.29; P = 0.76). In Experiment 3, tests were videotaped from 0830 h to 1330 h, and tapes were scored for time spent in each compartment. Birds were observed to spend more time in open- compared with solid-sided compartments (P = 0.02). To assess stress level of birds exposed to each type of enclosure, blood was collected from 24 commercial Hy-Line W36 hens housed long-term in either open (n = 12) or solid (n = 12) cages, and heterophil:lymphocyte (H:L) ratios were determined. Birds in solid cages had higher H:L ratios than did birds in open cages (P = 0.02), indicating a greater stress response. These data would suggest that hens may prefer greater visual access to their surroundings afforded by open cages.