What affects nesting behaviour in broiler breeders? The role of motivation, physical ability and social opportunity

Broiler breeders have a different genetic background from laying hens, since they have been selected for fast growth of their offspring. Selection for fast growth negatively affects the reproductive system, but the behaviour of broiler breeders also seems affected. They tend to lay more eggs outside the provided nests (so called floor eggs) compared to laying hens. Floor eggs are a sign of reduced welfare, the collection of floor eggs is time consuming and floor eggs have a lower saleability and hatchability than clean nest eggs. This study aimed to expand and update our knowledge on the factors involved in nesting behaviour of broiler breeders. The experimental work was structured around the Motivation-Ability-Opportunity (MAO) model, which states that the motivation to lay an egg in the nest is modified by the ability and opportunity to perform it. Looking first to increase this motivation, we found that broiler breeders have a clear preference for wooden nests compared to plastic nests. Hens were observed to choose their nest site location during the first weeks of egg production and are unlikely to alter this location. The prevention of floor eggs should thus get extra attention during the start of the egg production. Secondly, leg health problems, including foot pad dermatitis and lameness, or a high body weight might limit the ability of the hen to reach the nest. Foot pad dermatitis was found to be a common problem in broiler breeders, but no relationship was found between leg health and of floor egg percentage. Lastly, it was studied whether flock mates hamper the opportunity to enter the nest. Gregarious nesting, where a hen prefers a nest with other hens present over an empty nest, can lead to insufficient nest space. Excessive gregarious nesting was found to be partially caused by the genetic background of broiler breeders and seems to contribute to floor laying behaviour. The role of males in nesting behaviour of broiler breeder hens, although we found differences in mating activity depending on the litter size and altered spatial behaviour with more aggressive male behaviour. To conclude, nest design influences the motivation of broiler breeders to lay an egg in the nest, but the opportunity to visit the nest might be constrained by excessive gregarious nesting and male behaviour. Leg health problems do not seem to limit the ability to reach the nest or are overruled by the high motivation to get to the nest.