The Animal Sciences Group believes it may be possible for laying hens to produce mostly – or even exclusively – female embryos. This can help reduce the number of day-old roosters that are killed every year in the Netherlands, which now amounts to tens of millions. The process of sexing and killing day-old chicks has lead to much societal protest; therefore the ASG has been asked by Minister of Agriculture Verburg to look for other solutions.
"The most elegant solution is, of course, for the laying hens to produce only female embryos," explains Dr. Henri Woelders, lead author of the research report ‘Alternatieven voor doding van eendagskuikens’ (Alternatives for killing day-old chicks).
This solution is not purely theoretical, because there are indications that under certain conditions hens can generate more egg cells with W-type sex chromosomes. In that case, many fewer male embryos would be produced. With birds, males have two of the same kind of sex chromosome (ZZ) and females have two different kinds (ZW), which is exactly the opposite of mammals.
Another possible solution is to detect indicators such as sex hormones immediately after a fertilized egg has been laid. Now this can only take place only after day 13. "If you could do this on day 0, 'male' eggs could still be used in egg products," suggests Woelders.
A third possible solution referred to in the report is that there may be natural chicken mutations which lead to a greatly reduced number of male animals; this is caused by the early death of male (ZZ) embryos. For example, various cases are described in the literature where specific combinations of alleles lead to sex-linked embryonal death. Genetic lines could then be established in which the lethal combination of alleles can occur in the male embryos.
Minister Verburg has now requested the ASG and the Rathenau Institute to conduct an ethical and social review of the various alternatives. In addition, a feasibility study will be conducted at the ASG to map out a number of alternatives in greater detail.