Evaluation of eggshell quality characteristics in relation to the housing system of laying hens

To investigate the influence of housing system on eggshell quality characteristics, fourteen samples of eggs laid by brown hens of known ages and breeds, reared in conventional cage, free-range, barn and organic systems, were evaluated. The eggs were directly supplied by four poultry farms, each with different housing systems. The following parameters were determined: cracks percentage; egg weight and surface area; equator diameter, height and shape index; percentage of eggshell; eggshell index and shell thickness. Breaking strength of eggshell was evaluated using an Instron dynamometer equipped with a plate and a probe (8 mm diameter) as compression elements. Significant differences were observed for egg weight, surface area, and shell thickness (p≤0.001) among housing systems, with thicker shell from barn system and a tendency to bigger eggs in organic production. The variables related to shell strength and hardness seemed to be less affected by the housing system. Only displacement, Young Modulus and slope of the stress/strain curve obtained with the probe assay showed significant differences (p≤ 0.05), but with a partial overlap of the different groups. Eggs from barn system showed a higher deformability than free-range and organic eggs, and a lower hardness than free-range eggs. The “poultry farm” factor seemed to affect eggshell characteristics much more than “housing system”. In fact, when the samples were classified by producer, significant differences were observed for egg weight, surface area, equator diameter, height, and shell thickness (p ≤ 0.01). Moreover strength, displacement and energy at breakpoint also resulted significantly different (p ≤ 0.001). In conclusion, shell characteristics are not clearly influenced by housing system but seem to be more affected by producer management and other factors such as hen age and breed.