Sexual dimorphism during egg incubation and development of ovosexing methods

International audience

English. One of the main problems facing the poultry industry is the lack of economic value of male chicks from the laying hen production chain, due to their low meat yield and poor quality. Indeed, as the selection of breeding hens is based on productivity and egg quality criteria, the adults from laying strains are animals with poorly developed carcasses and low muscle yields. As a result, while the females are bred to produce table eggs, the males cannot be sold for their meat, which does not comply with European meat sales standards. Prior to the publication of government decrees in certain European countries, male chicks were killed one day after hatching. In France, this issue concerned nearly 50 million male chicks. This awareness that has been widely publicized in recent years and questioned the ethics of laying hens production, has led to the publication of a French decree on February 5, 2022, banning the killing of male chicks from Gallus gallus breeds selected for the production of table eggs. Three alternatives have been proposed: 1) raising the brothers of laying hens and identify new economic markets, 2) evaluating the performances of new genetic crossbreeds between broiler and layer lines, where the females would be raised for their eggs, and the males for their meat (dual-purpose breeds), 3) developing ovosexing tools to detect then eliminate male eggs rather than male chicks. The latter approach has been the most popular, as it possesses many advantages in terms of implementation at the hatchery level and acceptability to consumers, citizens, and professionals. This review will first introduce the socio-economic context associated with the production of egg-laying hens. It will detail a few physiological landmarks related to avian embryology and sexual dimorphism during embryonic development, which will help to better understand the technical bases and constrains for the development of ovosexing methods. The presentation will also give an overview of the recommendations for euthanasia of sorted male eggs that depend on the developmental stage of the embryo, and the management of hatchery by-products. Now that several ovosexing methods are on the market, the next challenge is to improve existing methods or develop new ones so that they are effective at very early stages of development, on all types of egg-laying strains, while remaining affordable for professionals and consumers.