Bielefelders and Other Autosex Chickens

Bielefelder chicks, like those of other autosex breeds, may be sexed at the time of hatch based on the color and markings of the chicks’ down. As is true for sex link chickens, the autosexing phenomenon takes advantage of genes that occur on the chickens’ sex chromosomes. Unlike hybrid sex links, though, autosex chickens will breed true, passing the color sexing trait to all future generations. Here’s a brief exploration of how this works in Bielefelders and other autosex chickens.

Sex Linkage

As you probably know, a rooster has two Z sex chromosomes (ZZ). A hen has a Z and a W (ZW). These sex chromosomes carry numerous genes, most of which have little to do with sex. Each Z chromosome, for example, carries some 1,000 genes.

Any trait that is influenced by genes on either a Z chromosome or a W chromosome is a “sex linked” trait. A trait expressed by genes on the W chromosome can appear only in hens. A trait expressed by genes on the Z chromosome are likely to occur in hens, because they have only one Z. A rooster, with two Z chromosomes, could carry genes for a trait on one chromosome, while the other chromosome carries genes that suppress expression of that trait.

A hen can pass her Z gene only to her sons and her W gene only to her daughters. So when you mate the right combination of breeds, cockerels inherit the hen’s color, pullets inherit the rooster’s color.

Highly simplified, that’s autosex. Most autosex breeds, including Bielefelders, are developed from barred breeds, gold/red/brown breeds, and/or white breeds carrying a silver factor.

As it turns out, a lot of these breeds already exhibit autosex linkage. However, the trait is typically not emphasized through selective breeding. Accuracy can therefore be 80% or less. Compare that to 100% for Bielefelders and other deliberately autosex chickens.

Autosex Origin

The autosexing idea and the term autosex originated with Dr. Reginald Punnett, a professor at the Genetical Institute at Cambridge University, and his assistant Michael Pease. They found that newly hatched chicks can be color sexed when a barred hen is crossed with a breed having a solid plumage color other than black. (Without the gene for barring, barred breeds would have black plumage.)

In barred and cuckoo breeds, such as barred Plymouth Rock and cuckoo Marans, the Z chromosome carries the gene for barring. Roosters therefore have two barring genes, while hens have only one.

A rooster’s bars are wider than a hen’s, and day-old cockerels tend to have paler down than pullets. Both have white head spots, but those of the pullets tend to be smaller and more compact.

To exaggerate the differences, the fellows at Cambridge crossed brown roosters with barred hens. The resulting pullets had dark chipmunk stripes on their backs, a dark bar across their eyes, and a small light spot on their heads. The cockerels’ are paler with a silvery sheen, and a large yellow patch on their heads.

This combination was introduced as a pure breed in 1928. Because it resulted from crossing a Campine rooster with a barred Plymouth Rock hen, it was called a Cambar.

The Cambridge group came up with the term autosex linkage to distinguish their true chicken breeds from sex link hybrids. They went on to create other combinations using barred Plymouth Rocks. In all breeds, the cockerels had lighter down than the pullets.

The names of these new breeds are a combination of the names of the original crosses: Ancobar (Ancona x barred Rock), Cobar (Cochin), Rhodebar (Rhode Island Red), Welbar (Welsumer), and so forth. Most of these breeds are now either extinct or extremely rare.

Autosex Chickens

An exception is the Legbar (Leghorn x), which remains popular to this day. The Cambridge fellows developed the Legbar by crossing a number of breeds, including Araucana, in addition to brown Leghorn and barred Rock.

After about two decades of selective breeding, in the mid 1940s the autosex Legbar became a genetically stable breed. At maturity cream Legbar hens are grayish with a salmon breast. The roosters are creamy white with dark barring on the breast and tail. Other features of the Legbar include head feathers and eggs with blue shells.

In the 1950s Swedish pastor and famed chicken breeder Martin Silverudd introduced another autosex breed, one that did not rely on barred genetics. Silverudd developed these chickens by crossing white and brown Leghorns varieties.

This breed relies on the silver gene on the Z chromosome, one of the genes responsible for white plumage. It also relies on the gold/red/brown gene, also on the Z chromosome. The silver gene inhibits gold/red/brown pigmentation.

A white hen with the silver gene crossed with a red male gives her silver gene only to her sons. They therefore inherit one red gene (from the rooster) and one inhibiting silver gene, making them basically white. The pullets inherit one red gene plus other color influencing genes, but not silver.

In the case of Silverudd’s breed, day-old pullets are dark reddish-brown. The cockerels are more yellowish. At maturity the roosters are mostly white, while the hens are brown with black and white “flowery” spots (millefleur pattern). Because the original cross occurred in 1955, the breed name is Fifty Five Flowery (also written as 55 Flowery).

Bielefelder Chickens

In the 1970s, a German fellow by the name of Gert Roth introduced a new autosex breed: Bielefelder. The name comes from the city of Bielefeld in North Rhine-Westphalia. Roth used a number of different breeds including barred Plymouth Rock, Rhode Island Red, New Hampshire, Wyandotte, and a Dutch breed called Cuckoo Malines.

Bielefelder pullets are dark brown, with chipmunk stripes that extend from the head down the back, and a black bar across the eyes. Cockerels are light brown with a white patch on the head. At maturity the hens are brown with a subtle white and gray cuckoo pattern. Roosters are cuckoo throughout, with orange hackles, backs, and saddles and black tails and breasts. The cuckoo pattern is similar to barring, but with blurred stripes.

In the mid 1980s Roth introduced Bielefelder bantams. To develop this smaller breed, he used New Hampshire bantams, barred Rock bantams, and Welsumer bantams.

Made in the USA

Lest you think all autosex breeds come from overseas: In the 1930s Horace Dryden of Modesto, California, crossed white Leghorns with barred Rocks to create the California Gray. Here, again, the pullets are darker than cockerels. Although all the chicks are yellow with black body spots, only the pullets have head spots.

At maturity, California Gray hens have a white and dark gray cuckoo pattern. The rooster is also cuckoo, but white and pale gray. Today this breed is used primarily to produce the hybrid sex linked California White.

Bielefelders and the other autosex chickens mentioned here are just a few of those now available. Since the sequencing of the chicken genome, we now have a better grasp of where the chicken’s plumage colors and patterns come from. I’m sure many more autosex breeds will follow.