Laying hen behavior. 1. Effects of cage type and startle stimuli.

The well-being of commercial laying hens plays an important role in egg production. Behaviors such as pacing, displaced preening, increased aggression, and redirected activities have been associated with stress in poultry. This study was conducted to determine whether two strains of commercial layers, reported to differ in level of excitability, behave differently in two types of commercial cages. DeKalb Delta and Hy-Line W36 hens, 40 to 45 wk of age, were housed six to eight per cage in open or solid-sided cages, at an equal density between cages. For each strain, there were six cages per cage type for a total of 24 cages. In the first five experiments, behavioral data were obtained at a distance of 1 m by instantaneous or scan sampling. These experiments included hen behavior in both types of cages with and without the presence of frustrating or startle conditions. Some significant differences in behavior existed within experiments but not consistently among all experiments. Sampling method did not affect reliability of data collection. Two trials were then conducted to determine whether the length of time to return to normal activity after a startle stimulus is influenced by the cage type or strain. In the first startle experiment, DeKalb hens returned to normal activity more quickly than did Hy-Line hens (P = 0.07); this strain difference was not found when the experiment was repeated. Cage type did not appear to affect the behavior of birds adversely, although neither cage type appeared to confer an advantage. No clear differences were found in behavior by strain or by strain within cage.

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.