Global variation and uniformity of eggshell thickness for chicken eggs

Damaged eggshells result in losses of eggs. Numerous efforts have been carried out to improve eggshell quality, which may lead to increased eggshell thickness. The conventional way of enhancing eggshell strength with thicker eggshell on average may be replaced by a new strategy to improve eggshell uniformity without increasing eggshell thickness. To achieve this, it is necessary to investigate global variation of eggshell thickness. In this study, we used 100 fresh eggs from 52-wk-old layers of a commercial brown-egg variety. To determine the global variation of eggshell thickness, 42 points for each egg along both longitudinal and latitudinal axes were selected to measure thickness using an eggshell thickness gauge. The eggshell thickness from blunt to sharp end varied significantly (P < 0.05). The area surrounding the blunt end was the thinnest (0.341 ± 0.025 mm), whereas the area surrounding the sharp end was the thickest (0.367 ± 0.023 mm). It was found that the thickness of the sharp end was the closest to the average thickness of the whole eggshell and could be considered as a valid measurement of eggshell thickness. A new parameter, eggshell thickness uniformity, was defined as the reciprocal of the coefficient of variation (1/CV) of eggshell thickness from 42 points of each egg and can be used to evaluate the eggshell quality. Eggshell thickness uniformity was positively correlated with breaking strength (r = 0.341; P < 0.01), suggesting that the parameter may be used as a potential selection criterion in breeding program to improve eggshell quality without increasing eggshell thickness.