Pressure load on keel bone and foot pads in perching laying hens in relation to perch design

The provision of perches in housing systems for laying hens is meant to improve hens' welfare by allowing a more natural behavior repertoire. However, the use of perches is associated with welfare problems, such as keel bone deviations and foot pad lesions, that may possibly result from high mechanical pressure load during extended perching activities. The aim of this study was to analyze peak force and contact area of hens' keel bones and foot pads on solid test perches of square, round, and oval shape with 3 different diameters each (experiment 1) and on commercially used perches (round steel tube, 2 sizes of mushroom-shaped plastic, and flattened round plastic) together with 2 prototypes of soft, round polyurethane perches (experiment 2). Test perches were covered with a pressure sensor film and 36 laying hens (18 Lohmann Selected Leghorn, 18 Lohmann Brown) were consecutively placed on each perch in an experimental cage during nighttime. Peak force (N/cm(2)) and contact area (cm(2)) were measured while hens were sitting and standing on the different test perches. Pressure peaks on the keel bone were approximately 5 times higher compared with single foot pad. On square perches, keel bone peak force was lower (P < 0.05) and contact area was larger (P < 0.001) compared with round and oval perches. In addition, peak force on foot pads in standing hens was higher on square perches (P < 0.05) compared with oval perches. Perch size did not affect peak forces on keel bones in sitting hens and foot pads in standing hens (experiment 1). On prototype perches, peak force on the keel bone was lower and contact area was larger compared with all commercial perches tested (P < 0.001). Peak force on foot pads was lower on prototype perches compared with steel perches (P < 0.01; experiment 2). Perches with a soft surface may possibly reduce keel bone and foot pad welfare problems in perching laying hens.