1 Department of Animal Science - Behaviour and stressbiology, Department of Animal Science, Science and Technology, Aarhus University2 Department of Bioscience, Science and Technology, Aarhus University3 Aarhus University, Department of Bioscience4 Department of Animal Science - Behaviour and stressbiology, Department of Animal Science, Science and Technology, Aarhus University
Gregarious nesting, where hens select already occupied nest boxes even when other nest boxes are unoccupied, is an unwanted behaviour in laying hens that may reduce animal welfare and pose a financial cost to the producer. It has been suggested that gregarious nesting is caused by the difficulties experienced by hens in distinguishing between nest boxes in long rows of identical boxes. Heterogeneity of nest boxes has therefore been suggested as a method to reduce gregarious nesting. To test this hypothesis two experiments were performed. Twelve groups of 13–15 ISA Warren hens 27 weeks of age were housed in pens with three adjacent nest boxes. In the first experiment six experimental groups were provided with three different appearing nest boxes (yellow walls, plastic flaps, standard) containing wood-shavings, and in the second experiment six experimental groups were provided with three different nesting materials (straw, peat, wood-shavings). In both experiments six control groups were provided with three identical nest boxes containing wood-shavings. Daily egg collection and video recordings were performed during both experiments (eight and seven days, respectively). The proportion of gregarious nesting was higher in experimental groups compared to control groups (P < 0.01). The pre-laying period did not differ between the experimental and control groups (P = 0.41). Numbers of visits to and eggs laid in nest boxes positioned either left or right were higher compared to nest boxes positioned in the middle in both the experimental and control groups (P < 0.05). Numbers of visits to yellow and standard nest boxes were higher compared to nest boxes with plastic flaps in front (P < 0.05). Furthermore, straw was preferred with regard to number of visits to and eggs laid in nest boxes compared to both wood-shavings (P < 0.01) and peat (P < 0.01) as nesting materials. Heterogeneity of nest boxes in the present experiments did not reduce occurrence of gregarious nesting. Instead, the combination of preferences for nest box position, appearance, and nesting material indicate that hens shared preferences for nest boxes positioned at the ends of the row, yellow walls, standard nest boxes, and straw as nesting material. We find it likely that this caused the increase in occurrence of gregarious nesting. Therefore it is suggested that only nest boxes positioned in the middle of rows should be made more attractive by providing preferred nest box appearances or nesting materials, thereby possibly reducing gregarious nesting.