Development with age of nest box use and gregarious nesting in laying hens

Abstract

Use of nest boxes is an important part of the behavioural repertoire of laying hens kept under commercial conditions. A special form of nest box use is gregarious nesting, which occurs when a hen given the choice between an occupied and an unoccupied nest site chooses the occupied nest site. Knowledge about gregarious nesting behaviour is limited, but welfare problems likely to be associated with it are scratches/wounds, heat stress, increased level of aggression, and excessive expenditure of energy. The benefits of the producer may also be affected by gregarious nesting due to an increased risk of broken or dirty eggs. The main objectives were to investigate the use of nest boxes according to their position and the occurrence of gregarious nesting with age. Twelve groups of 15 Isa Warren hens were housed in pens each containing three adjacent roll-out nest boxes only differing in position (left + corner, middle, and right). Nesting behaviour was video recorded for 5 days in each of five distinct periods: age 20, 26, 32, 38, and 44 weeks. The total number of visits and the number of gregarious visits were higher in the left nest box than in the other two nest boxes at all ages and higher at age 20 weeks than at the other ages ( P < 0.001). Also, more eggs were laid in the left nest box than in the other two nest boxes ( P < 0.001) and this did not change with age ( P > 0.05). The proportion of gregarious visits of the total number of visits, where the hens had a choice between gregarious or solitary nesting, was higher at age 20 weeks than at older ages ( P < 0.001). It is suggested that young hens inexperienced in nest box selection will tend to visit the same nest boxes as more experienced individuals. As they gain experience individuals will tend to rely more on their own experiences in selection of nest locations, causing the found decrease in frequency of gregarious nesting after age 20 weeks. A general preference for corner and end nest boxes is suggested to have triggered the initial use of the left nest box by the first hens coming into lay and to have maintained the observed high level of gregarious nesting throughout the study.