Autosexing is when pure bred day old chicks can be sexed by their different appearances when they have hatched. This is a characteristic that is highly desirable so that chicks can be raised as guaranteed pullets, keeping food costs down. There are a number of breeds (note: pure bred birds) that will autosex, the Cream Legbar being an example. The offspring will breed true and remain autosexing.
It was Professor Reginald Punnett at the University of Cambridge in the UK who was instrumental in the study of autosexing poultry during the 1920’s that came up with a theory that he later proved.
Punnett’s theory was that the gene responsible for barred colour patterns acted differently in male and female chicks. Males received two barred genes whilst females only one, which meant the males would be lighter than the females.
Punnett exhibited the Cambar, (the World’s first autosexing chicken breed) at the World Poultry Congress in 1930.
Whilst being able to sex chicks as they were born by their down colour was set to revolutionise the poultry industry, sadly this was not so. The autosexing breeds were seldom the best layers and while a lot of work was subsequently done to improve this, the poultry industry took a sudden sharp turn in the 1950’s towards higher production, greater feed efficiencies and factory farming with the Hybrid chicken. These birds, descended from pure bred stock could also be sexed as day-olds thanks to sex-linkage.
Sex linked birds can sexed as day old chicks by their different appearances like the autosexing breeds and this is what is used extensively these days on commercial poultry farms.
Sex linkage is when two different breeds of (pure bred) birds are crossed. For example, the Bovan Nera (AKA Black Rock, Black Star) are a sex-linked cross of the Rhode Island Red X Barred Plymouth Rock. The offspring will not breed true from these crosses.
Autosexing chicken breeds
The following chickens are autosexing:
Amrock, Ancobar, Barnebar, Bielefelder Kennhuhn, Brockbar, Brussbar, Buffbar, Cambar, Cobar, Cream Legbar, Dorbar, Gold Legbar, Hambar, Niederrheiner, Norske Jaerhon, Oklabar, Polbar, Rhodebar, Welbar, Whealbar, and Wybar.
Most of these breeds are either extinct or extremely rare these days. The most popular and easily obtainable is the Cream Legbar which has probably remained popular with backyard chicken keepers because of their blue eggs.
Autosexing duck breeds
Why are there no autosexing duck breeds? Well, ducks can be vent sexed when young and there are obvious differences in domestic ducks between the duck and drake when they are adults so there has never really been a need for autosexing duck breeds.
Autosexing goose breeds
Autosexing example: The Cream Legbar
Cream Legbars are autosexing poultry. They are a pure breed but were originally created from a cross between the Brown Leghorn, Araucana and Barred Plymouth Rock amongst others. In this example, we can see that young chicks can be sexed by the colour of their down shortly after hatching.
The ‘barring’ pattern is sex-linked, i.e. the males have two chromosomes for barring and the females only one. Day old chicks have a light patch on the top of the head. When the barring is combined with brown colouring, the light spot on the head of the females is small and there is a clearly defined dark brown stripe down the back. The stripe down the back of male chicks is much fainter and there is a light yellow patch that covers most of their head. The down of the male chick is also much paler and silver.