The interaction effects of the naked neck gene and housing system on egg production, egg quality, blood biochemical parameters and immunity of laying hens under hot climate

Abstract

Objective: Poultry producers use alternative housing arrangements, such as free-range systems, to allow birds to express their natural behaviors and to enhance consumer confidence in poultry products. Free-range systems provide hens with access to open spaces and better airflow, offering opportunities for thermoregulation through natural behaviors such as seeking shade or dust bathing. Compared to confined cage conditions, this can help reduce the negative effects of heat stress. In this study, we examined the productivity of laying hens segregated for the naked neck gene (Na) and raised in two distinct housing systems. Methods: A total of 540 laying hens, 24 weeks of age, were randomly assigned to a 2×3 factorial design consisting of three genotypes (NaNa, Nana, and nana) and two housing systems (wire cages and free-range pens). Productive performance, egg quality characteristics, immune response, and blood parameters were evaluated over a three-month period during the hot summer season. Results: The results showed that introducing the Na gene into chickens raised under hot climate conditions improved egg production, cell-mediated immunity, and eggshell strength. A significant reduction in blood cholesterol levels and the cumulative percentage of broken eggs was observed in naked neck genotypes (NaNa and Nana) compared to the normally feathered genotype (nana). Hens kept in cages produced significantly heavier eggs compared to those in the free-range system. Laying hens kept in a free-range system exhibited a higher relative yolk weight and an increased shell percentage. Additionally, a significant decrease in plasma cholesterol levels was found in layers raised in free-range systems compared to those in wire cages. Eggs produced by hens reared in free-range systems also had a darker yellow yolk color compared to those from caged hens. Conclusion: Introducing the Na gene into laying hens raised in free-range housing could be beneficial for improving egg production, immunity, and egg quality under high ambient temperatures.