Predicting hairline fractures in eggs of mature hens

Eggshell damage poses a serious problem for the consumption egg industry. Increasing the maximum age of laying hens will increase eggshell damage due to loss of shell strength. This poses a serious problem for automatic collection, packing, and transport. We performed a model based study focused on hairline fractures in eggs of 88-week-old hens, and simulated side collisions on 1,235 eggs using a specially designed pendulum. The kinetic energy at the moment of impact was related to the accelerations measured by an electronic egg going through the transport chain. Further, several egg mechanical properties were measured. For collisions with a realistic impact, fracture occurrence correlated negatively with dynamic stiffness (14%), mass (15%), shape index (9%), and damping ratio (12%). We manipulated the data set to investigate the influence of improving egg properties. Removing the least favorable 50% of the eggs based on stiffness and mass resulted in a moderate reduction of fracture occurrence, from 7.7% down to 4.4%. The peak acceleration of an egg running through the transport chain lies typically in the range of 15 to 45 g. Our model predicts that a moderate decrease from 30 g down to 20 g will result in a drastic reduction of fracture occurrence from 7.7% down to 0.3 to 1% (95% confidence region), whereas an increase to 40 g will increase fracture occurrence to 42 to 55%. The model predicts that severe collisions pose a relatively high risk for eggshell damage, which suggests that a reduction of collision severity is of first priority when increasing the age of laying hens.