Population size, cage area, and dominance rank effects on productivity and well-being of laying hens.

The effect of two cage population sizes (four vs. six/cage) and two cage area treatments (316 cm2 vs. 406 cm2/bird) were compared in a nonconfounded design while maintaining feeder space constant (8.9 cm/bird) for egg production performances and behavioral and physiological indicators of well-being of laying hens. Egg production rates were determined for all members of each cage group (palpations at 48 to 50 wk) and on a cage group basis (20 to 60 wk). Heart weights, plasma corticosterone levels, durations of tonic immobility (TI), and plumage conditions were compared for top and bottom birds in the dominance ranks. Significant reductions in egg production were observed for low ranking hens in the high density (4 and 6/316-cm2) treatments. In addition, high ranking hens of the 6/316-cm2 treatment produced fewer eggs than high ranking hens in the 4/316-cm2 treatment. When high and low ranking individuals were housed in single-hen cages, egg production was improved relative to performances in the social environments. Heart weights of hens, as a percentage of body weight, were increased in the low ranking hens and for hens in the smaller cage size. Plasma corticosterone did not prove to be a useful indicator of well-being. Low ranking individuals had greater durations of TI but differences in feather condition were not detected. The results support the contention that appropriate population sizes and cage space allocations can be determined that will optimize the performance and welfare of layers in cage environments.