Floor eggs, which are defined as eggs that hens lay off-nest, are a major issue in cage-free layer poultry systems. They create additional work for farmers because they must be collected by hand. They are also usually soiled or broken, which results in economic losses. Nonetheless, knowledge about the genetics of nesting behavior is limited. The aim of this study was to estimate genetic parameters for traits related to nest preference for laying and to time spent in the nests used for laying (laying duration). Two pure lines of laying hens were studied: 927 Rhode Island Red and 980 White Leghorn. Electronic nests were used to record the nesting behavior of these hens in floor pens from 24 to 64 weeks of age. Nest preference was studied based on the mean distance between nests used for laying and the percentage of nests used for laying. Laying duration was studied based on mean laying duration, mean duration in the nest before laying, and mean duration in the nest after laying. Genetic parameters were estimated for each line using a restricted maximum-likelihood method applied to a pedigree-based multi-trait animal model. Estimates of genetic parameters were similar for the two lines. Estimates of heritability ranged from 0.18 to 0.37 for nest preference traits and from 0.54 to 0.70 for laying duration traits. Estimates of genetic correlations of these traits with clutch number or mean oviposition time were favorable. Positive genetic correlations were estimated between nest preference and laying rate in the nests or nest acceptance for laying (+ 0.06 to + 0.37). These results show that genetics influences traits related to nest preference and laying duration. Selecting hens that have no preference for particular nests and spend little time laying in the nests could help optimize nest use, reduce their occupation rate, and thus decrease the incidence of floor eggs in cage-free systems. Genetic correlations of these traits with other traits of interest related to hen welfare and egg quality have yet to be estimated.

In cage-free systems, laying hens must lay their eggs in the nests. Selecting layers based on nesting behavior would be a good strategy for improving egg production in these breeding systems. However, little is known about the genetic determinism of nest-related traits. Laying rate in the nests (LRN), clutch number (CN), oviposition traits (OT), and nest acceptance for laying (NAL) of 1,430 Rhode Island Red (RIR) hens and 1,008 White Leghorn (WL) hens were recorded in floor pens provided with individual electronic nests. Heritability and genetic and phenotypic correlations of all traits were estimated over two recording periods-the peak (24-43 weeks of age) and the middle (44-64 weeks of age) of production-by applying the restricted maximum likelihood method to an animal model. The mean oviposition time (MOT) ranged from 2 h 5 min to 3 h and from 3 h 35 min to 3 h 44 min after turning on the lights for RIR and WL hens, respectively. The mean oviposition interval ranged from 24 h 3 min to 24 h 16 min. All heritability and correlation estimates were similar for RIR and WL. Low to moderate heritability coefficients were estimated for LRN (0.04-0.25) and moderate to high heritability coefficients for CN and OT (0.27-0.68). CN and OT were negatively genetically correlated with LRN (-0.92 to -0.39) except during peak production for RIR (-0.30 to +0.43). NAL was weakly to moderately heritable (0.13-0.26). Genetic correlations between NAL and other traits were low to moderate (-0.41 to +0.44). In conclusion, CN and OT are promising selection criteria to improve egg production in cage-free systems. NAL can be also used to reduce the number of eggs laid off-nest in these breeding systems. However, variability in MOT must be maintained to limit competition for the nests.

Les effectifs de poules pondeuses élevées dans des systèmes alternatifs à la cage augmentent en Europe. Dans ces systèmes, les poules évoluent librement dans des groupes de grande taille et doivent pondre dans des nids. Les sélectionneurs ont besoin de mesurer les performances de ponte individuelles des poules dans ces conditions très différentes de la cage. Pour cela, des nids électroniques ont été développés. Ces nids permettent de mesurer les critères de sélection classiques de production d’œufs et de qualité d’œuf, mais également de nouveaux caractères de ponte liés au comportement précédant la ponte et au comportement au nid. Les caractères de rythme de ponte des poules peuvent aussi être mesurés précisément grâce à l’enregistrement de l’heure de ponte. Les connaissances sur le déterminisme génétique de ces caractères de ponte, encore partielles, offrent d’ores et déjà des perspectives de sélection pour améliorer les performances de ponte dans ces systèmes d’élevage ainsi que la capacité d’adaptation des animaux et leur bien-être.

The number of laying hens raised in cage-free systems has increased in Europe. In these breeding systems, hens live freely in large groups and must lay eggs in nests. Breeders need to measure the individual laying performance of hens under these very different cage conditions. To do so, electronic nests have been developed. These nests enable to measure regular selection criteria, i.e. egg production and egg quality traits, but also provide access to new egg-laying traits, related to pre-laying behavior and nesting behavior. Reproductive rhythm traits can also be measured precisely by recording the laying time. Although there is little knowledge of the genetic background of these egg-laying traits, there are already selection opportunities for increasing egg-laying performance in these breeding systems as well as improved adaptation capacity and welfare.