Measuring the eggshell strength of 6 different genetic strains of laying hens: techniques and comparisons.

1. Eggshell quality was compared in 6 different strains of laying hens. Three strains were commercial; the three others were experimental. 2. Four different variables describing the strength of eggshells were investigated. Three of them were the classical ones eggshell thickness, shell stiffness measured during quasi-static compression and breaking force. Dynamic stiffness, introduced by Coucke (Ph.D. Thesis, KU Leuven, 1998), was the 4th. The fact that this measurement is dynamic could be helpful in genetic selection for eggshell breakage, because forces applied to the egg in practice are dynamic, rather than static. 3. Hisex White hens produce eggs with the strongest eggshell, in terms of all 4 eggshell variables. However, their shell quality in terms of breaking force did not remain constant over the laying period, unlike 4 other strains. 4. All strains showed a decline in quasi-static stiffness over time. 5. The eggshell thickness of three strains showed a decline over time. 6. Dynamic stiffness remained constant or improved in all strain. 7. All variables describing the mechanical eggshell strength gave different information.