End of culling day-old male layer chicks: ovosexing as the method of choice

Abstract

One major issue 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 quality. This issue concerns nearly 50 million male chicks in France and 7.5 billion chicks worldwide, that were (until recently) culled after sexing and sorting at hatching, which raise a major ethical issue. In recent years, a wide media coverage has raised awareness of the society about this issue, which has led to the publication of a French decree on February 5, 2022, banning the killing of males from Gallus gallus breeds selected for table egg production. Three alternatives have been proposed: 1) raising the brothers of laying hens and identifying 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 sexing tools in ovo to detect then eliminate eggs containing a male embryo 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 introduces the socio-economic context, provides an update on current in ovo sexing techniques, while introducing some physiological landmarks related to avian embryology, which allows a better understanding of the constraints associated with the development of ovosexing techniques at early stages of development.