Genetic variability of nesting behavior and egg production traits for laying hens raised in a cage-free system

In laying hens, the importance of cage-free systems (barn, free-range and organic) has increased in recent years. These systems require that laying hens lay their eggs in nests. Indeed, off-nest laid eggs impair the production performance of the flock because they are most of the time down graded or lost. Consequently, select laying hens on nesting behavior would be a good opportunity to reduce off-nest laid eggs and improve egg production. However, little is known about such traits. Our study aimed at estimating genetic parameters of nesting behavior traits and their genetic correlations with a production trait, in order to evaluate their potential inclusion in breeding programs. Data were continuously recorded on laying hens raised in a barn thanks to individual electronic nests, which use radio-frequency identification of hens. Nesting behavior and production traits were recorded between 24 (peak of egg production) and 64 (middle of egg production) weeks of age on two pure lines: 1,430 Rhode Island Red hens (RIR) and 1,008 White Leghorn hens (WL). The nesting behavior traits studied were the mean laying duration (MLD), i.e. the mean time spent in the nests to lay, the mean distance between nests of laying (MDN) and the rhythm of lay, like clutch number and the mean oviposition time (MOT). The egg production trait studied was the laying rate in the nests (LRN). Genetic parameters were estimated by applying there stricted maximum like lihood method to an animal model. High (0.55 and 0.68) and moderate (0.32 and 0.37) heritability estimates were found for MLD and MDN respectively. For these two traits, null or favorable genetic correlations with LRN were estimated. Select laying hens with a low MLD and high MDN, i.e. high exploratory behavior, could help to reduce off-nest laid eggs. In the two lines, high heritability estimateswere found for clutch number and MOT with values between 0.40 and 0.66. For LRN, heritability estimates were 0.09 and 0.25 for RIR and WL respectively. Strong negative genetic correlations (-0.72 and -0.61) were estimated between clutch number and LRN, indicating that select laying hens with a low clutch number could increase LRN. Genetic correlations between MOT and LRN were lower with estimates values from -0.04 and -0.44 for RIR and WL respectively. The existence of a genetic background for nesting behavior traits is promising to identify quantitative traits locus and candidate genes implicated in the expression of such traits.