Differences in nest preference of laying hens and their motivation to work for access to the nest.

In previous experiments we repeatedly found a small number of hens constantly choosing litter (wood shavings) for laying. We were interested in whether there are differences in prelaying behaviour between these hens (litter-layers) and hens laying in nest-boxes (nest-layers). We hypothesized that litter-layers will be more frustrated than nest-layers because they might not be able to find an appropriate nest site. The experiment was carried out with 21 LSL-laying hens which were individually housed from week 19 on. In each pen two trays with litter served as potential nest sites whereas one tray was complemented with a wooden nest-box. Eggs were collected daily and their position was noted. A push-door was placed in front of each potential nest site so that the hen had to push the door open to gain access to the respective nest site, but was left open until the 15 egg laid. Then a minimal resistance of 350 mN was set to push the door open. On the day of the 19 egg the behaviour in the last hour before oviposition was videorecorded for analysis of the following elements: foraging, resting, exploring, nest-inspection and nesting. The mean time spent on each behaviour was calculated and analysed for differences between nestand litter-layers using a Kolmogorov-Smirnoff-two-sample-test. Nest-layers spent significantly more time resting than litter-layers (28.5% ± 13.3 vs. 12.6% ± 10.4; p 0.05) were found for foraging (13.9% ± 7.0 vs. 14.6% ± 10.9) and nesting behaviour (34.2% ± 15.7 vs. 30.6% ± 16.5). As a high level of exploring suggests restlessness and may be regarded as an indicator for frustration, we conclude that in our experiment litter-layers had difficulties to find a suitable nest site and therefore continued searching throughout the last hour before oviposition. We conclude that mislaid eggs in commercially housed flocks may be due to a number of consistent floor-layers which do not perceive the offered nests as appropriate nest sites. In respect to the welfare of these hens as well as to the economic losses due to floor eggs we strongly suggest further studies on how nest sites have to be designed to fulfil the expectations of litter-layers.