Extraneous egg shell calcification as a measure of stress in poultry

The incidence of eggs showing abnormal shell calcification amongst those produced by hens kept in individual battery cages, hens kept in battery cages in groups of 3 and hens kept in battery cages in groups of 4 was studied. There was good agreement between observers in the assessment of abnormal eggs. Hens kept in individual cages laid fewer abnormal eggs than hens kept in groups of 3 or 4. There was no significant difference in the incidence of abnormal eggs between hens kept in groups of 3 or 4. The results of this study support the idea that the incidence of eggs showing abnormal calcification may provide a quick and reliable method of measuring stress in hens which lay brown shelled eggs.