![]() ![]() ![]() The history of hen’s egg sexing by molecular spectroscopic methods is illustrated and summarized in Fig. During the past years, several studies were published about in ovo sexing by Raman and fluorescence spectroscopy. Therefore, these methods will meet the concern of animal welfare and are considered as favorable for a broad practical use in large-scale hatcheries. Molecular optical spectroscopic methods have the advantage of being applicable in a very early state of incubation. The endocrinological method is already used commercially, but sex determination cannot be made before the 9 th day of incubation. Techniques based on in ovo determination of feather color are solely applicable in the late incubation phase and only for brown layers. Currently, it is scientifically accepted that the chicken embryo is not yet capable of nociception before the 7 th day of incubation. It should be noted that occasional also not reproducible studies of sexing eggs were published, for examples by morphological measurements of the egg, which are not considered in Table 1.Įxactly when the ability to nociception begins is not known with certainty. Table 1 summarizes the current bioanalytical methods for in ovo sexing of hatching fertilized eggs. ![]() However, methods that allow the identification of female and male embryos by means of genetic engineering are publicly criticized and will probably not be used due to a lack of consumer acceptance, at least in Western European countries. Laying hens that develop from these embryos as well as the eggs they lay are not genetically modified. In the female embryos, the unchanged Z and W chromosomes are active. At production level, homozygotic male embryos (ZZ) can be identified due to their fluorescence and eggs can be sorted out. A green fluorescent protein gene is micro-injected in the embryo at the parental level and place on the female Z chromosome. Another strategy to avoid the killing of hatched male chicks is based on CRISPR/Cas 9 gene editing in parent flocks. Several groups have investigated techniques for an in ovo sexing by analyzing individual marker molecules or sum parameters like the biochemical profile of embryos. Consequently, the in ovo sexing of chicken eggs has been a world-wide research interest since over a decade. Therefore, the early sexing of fertilized eggs is considered as the key to overwhelm the culling of unwanted male day-old chicks. In Germany, the culling of hatched male day-old chicks has been banned by law since 2022, and from 2024 the culling of chicken embryos has to be done at an early state but not later than day 7 of incubation. For example, the United Egg Producers stated to stop the mass culling of male chicks as soon as there is an ethical and economically feasible alternative. In many states, egg producers are being pressured to phase out chick culling. Male chicks of layer lines are divided from their sisters within a day of hatching and culled, which is one of the biggest animal-welfare issues in the egg production. Graphical Abstractįarm chicks are bred for two purposes: to lay eggs or to produce meat. The hatching rate is not reduced compared to an equivalent reference group. The accuracy of sex determination is 96% for both sexes. It is shown that the observed sex-related differences in the fluorescence intensities are based on the embryonic hemoglobin synthesis. The fluorescence intensities of the spectral regions behave inversely with respect to sex. In ovo fluorescence was sequentially excited at 532 nm and 785 nm. ![]() In this study, a novel method based on two-wavelength in ovo fluorescence excitation is described. Optical spectroscopic methods enable an early determination of the sex. Although various methods have been developed and tested in recent years, practicable methods for sex determination are still missing which can be applicated in poultry hatcheries before the chicken embryo is capable of nociception and pain sensation. The in ovo sexing of chicken eggs is a current task and a prerequisite to overcome the mass killing of male day-old chicks from laying lines. ![]()
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