Near infrared optical spectroscopy: a new approach for sexing of domestic chicken eggs

Culling of day-old male chicks in laying hen production involves billions of animals every year worldwide. It raises serious concerns for animal welfare, which stimulated increasing research in the attempt to find sustainable alternatives. Optical spectroscopy was investigated with the aim to reveal the sex of domestic chicken embryos still in ovo. We demonstrate that a spectral analysis of the backscattered radiation, which is obtained by illuminating with a laser beam the flowing blood in the egg extra-embryonic circulation, delivers biochemical information based on Raman scattering and hemoglobin fluorescence. Sex-related differences in Raman and fluorescence spectra were identified already at day 3.5 of egg incubation. Chemometric methods exploiting both data provide correct sexing rates above 95%. Low-power near-infrared lasers are used for excitation, so that the measurement is damage-free. The overall sexing procedure barely affects the hatching rate. Moreover, sex recognition is obtained before onset of embryo sensitivity. Therefore, sexing of eggs in the early phase of incubation has the potential to replace chick culling.