Sex-linked breeding in poultry - Part 1
How to create crossbreeds where you can tell the sex of your chicks as soon as they're fluffed up
Sex-linking and autosexing: these are two terms that broadly mean the same thing.
They’re used in breeding, to refer to chicks where you can accurately and reliably identify the sex of the chick as soon as it’s hatched and the down has fluffed up.
Autosexing: this is a PURE breed where the chicks can be sexed at hatch, and where the sexing carries though the offspring.
It includes all the ~bar breeds (Gold and Silver Legbar, Cream/Crested Legbar, Rhodebar, Cambar, Barnebar, etc), and other well-known breeds like Plymouth Rock, Barnevelder, Welsummer, Rhode Island Red, and others.
Sex-linked: this is where the sex-linked chicks are the result of a very specific cross between breeds, or colours within breeds. The sexing ability does not necessarily carry through to the offspring.
It includes all the commercial layer varieties (ISA Brown, Hyline Brown, Lohmann Brown, Hisex, Bond/Barter Brown, Black and White, etc), as well as a range of easily-accessible crosses that anyone can do.
This series of articles covers sex-linked crossbreeds.
Please visit my article on autosexing for discussion of the autosexing pure breeds, including the “recipe” for creating most of the ~bar breeds.
About these articles
I’ve been researching these articles for months. It was going to be this nice simple single page on the topic (*insert wry laugh*). The more I researched, the more I found.
In the end, I had to break it up into multiple sections, because I had to do a proper job on it. And even then, what I’ve written is, I suspect, little more than an overview. For eg, I’ve only used sources available through online searches, or references found through those searches. If I started going through books, I’d probably find considerably more, take a year or more, and end up writing my own book on the topic …
The sections are:
Part 1: Introduction (this article)
You will need to pay and subscribe to see Parts 2, 3 and 4. Please do consider doing this; I’ve spent a lot of time researching!
Table of Contents
Down colour.
Down pattern.
Relative sizes of wing feathers.
Leg colour/pattern.
My other articles in the series
Discussions of actual sex-linked crosses
Books and online articles
Introduction: what is a sex-linked chicken?
It’s a crossbreed of two specific pure breeds, or two colours within a purebreed, where the offspring can be easily and reliably sexed as soon as the down has fluffed up. That is, they are sexually dimorphic at day-old.
The parent hen and rooster need to be of specific breeds or colours, and you can’t swap them, or the sex-linkage doesn’t work.
The sex-linked first-generation (F1) offspring are crossbreeds, with all that entails. It particularly means that the sex-linkage will not be inherited by their second-generation (F2) offspring in a reliable way.
This is called a “terminal” cross - not in the “makes the animal die” sense of terminal, but meaning “end of the line for this set of characteristics”.
All commercial layer varieties are sex-linked in some way. This is why you can reliably buy a Lohmann Brown pullet chick at day-old, without worrying about dealing with roosters down the track. The cockerel chicks are generally disposed of at hatch. (Commercial layers come with their own problems, however. See my related article for more).
It’s close to 100% reliable, but not absolutely. This is still ordinary breeding, and genetics always likes to throw a wild card into the mix.
Why do people want to identify the sex at hatch?
One of the most common questions asked in poultry groups is “what sex is my chick?”. People want to know early for a number of reasons, most of which boil down to the unfortunate fact that roosters have traits that make them unwelcome in smaller backyard flocks.
Roosters crow. Many find the noise annoying, particularly at close range and constantly.
Many Council areas do not permit the keeping of roosters in suburban blocks, because of the risk of noise complaints from neighbours.Roosters don’t lay eggs. Many people keep chickens strictly for their eggs, and that’s fine.
Roosters fight with eachother. Multiple roosters in a flock will often fight with eachother if there are hens present.
It is possible to keep “bachelor flocks” of roosters only - but they will be very noisy.Roosters shag. To be blunt, they’re randy buggers. They mate whatever hens are available as often as possible.
The ideal proportion is one rooster to 7-12 hens. Any more than that can see hens injured or even killed by constant rooster attention.Roosters are tasty. Some people do grow out their cockerels deliberately, for eating purposes; the best way to do this is to separate cockerels from pullets as soon as possible, to prevent injuries and fights and to allow for a fattening diet.
Hens fetch a premium price. Many people sell their chicks fairly young, and sexed female chicks fetch a premium price for their age.
People will quite happily pay $AU10 or even more for guaranteed female day-old chicks, regardless of breed or crossbreed, with commensurate price increases as they get older.
So knowing what sex your chicks are, as soon as possible, allows you to make sensible decisions before you get too attached to - and spend time and money and resources on - the prettier, friendlier chicks (as cockerels invariably seem to be!).
If you have no plans to use the cockerels at all, it is - brutal as this is to consider - a waste of resources to raise them. You just get attached, which results in the rather sad “free to a good home NOT FOR THE POT” ads that come around every year.
The regrettable fact is that there is not a good home for every cockerel that’s hatched and raised.
What about vent-sexing?
In years gone by, people used “vent-sexing” to identify the sex of their day-old chicks. This is not related to autosexing or sex-linking.
Vent-sexing is a mechanical method that can be performed on any chick at day-old to identify the sex. It requires experience and expertise to get accuracy higher than guesswork, and can only be performed on chicks up to 24 hours.
The technique involves squeezing the vent so it pops open, allowing the sexer to see inside and look for the minuscule “bumps” that identify either male or female chicks.
It’s not, however, a very straightforward process. According to this Backyard Poultry article:
… there are 18 different shapes possible with a two female and two male shapes that will appear as close matches for the opposite sex. Essentially, the view reveals a shape much like a necklace with “beads” of different sizes, largest in the center. The males have a round/globe-like center “bead”; the females have a flat or concave center “bead.”
As day-old chicks are quite fragile, and the differences between the male and female chicks is highly contextual, the technique has a high risk of damaging the chick AND of getting it wrong in the hands of the inexperienced. Commercial hatcheries would employ these expert people to do the sexing, so they could raise only pullets for egg production purposes, and dispose of the male chicks.
The development of commercial crossbreeds with sex-linked chicks reduces the skill level required to identify cockerels, as well as reducing the risk of injury to the chicks. The hatcheries save significant money with higher accuracy, lower-skilled workers, and fewer unnecessary deaths.
So, what do we use instead?
In sex-linked chicks, there will be one or more obvious things to look at. They’re easy to see with the unaided eye, don’t require any risky handling to make them visible, and very clearly and unequivocally identify either a female or male chick.
In all cases, these relate to features on a day-old chick, after it’s hatched and fluffed up. Many of these features will disappear within the first few days of hatching, and can’t be used reliably beyond that age.
They include:
Down colour. For eg, yellow pullets (female) and white cockerels (male).
Down pattern. For eg, a small white spot on the head (pullet) and large diffuse white patch (cockerel).
Relative sizes of wing feathers. For eg, irregular wing feathers (pullet) and same-sized feathers (cockerel). This does require a certain expertise to identify but, unlike vent-sexing, comes with a very low risk of damage to the chick.
Leg colour/pattern. For eg, dark legs (pullet) and light legs (cockerel).
Down colour or patterns - Gold, Silver, barred
This is probably the most common sex-linked cross. There are genetic reasons for why it works reliably, and I don’t actually understand them at all, because chicken genetics isn’t something I’ve concentrated on to this point. There’s a bit more detail in the longer article.
Suffice to say, then, that for Gold/Silver/Barred sex-linkage to work, it requires a purebreed “gold" male (rooster or cockerel) over (ie mated with) a purebreed “silver”, or a barred, female (pullet or hen).
Note:
It doesn't work the other way around.
The parent birds must be pure breeds, as crossbreeds will have too many other genetics kicking around to produce a reliable result.
It doesn’t work for the first-cross offspring.
It works once, and once only - a “terminal” cross. In this sense, “terminal” doesn’t mean “fatal”; it means “the identifying characteristics won’t carry through to future generations”.
The result is chicks that have different-coloured down as soon as they fluff up from hatching.
Broadly:
gold male over silver female gives buff/gold/brown female chicks and white/yellow/silvery male chicks
gold male over barred female gives plain black female chicks and black with white spot male chicks.
More details on actual breeds and mixes are in the following articles:
Feather-sexing
Any discussion about sexing chicks invariably comes up with this feather-length diagram, or something similar.
Photo by Dr. Jacquie Jacob, University of Kentucky.
The thing is that it IS reliable, but only in very particular breeds or crossbreeds; ones with the slow-feathering gene.
It also only applies to day-old chicks, and it can’t be broadly applied to all breeds or crossbreeds.
It’s created when a normal-feathering male (cockerel or rooster) is mated with a fast-feathering female (pullet or hen).
In a first-cross sexlink, this involves mating a Mediterranean breed male (for example Leghorn, Ancona, Minorca) with a specific heavy-breed dual-purpose hen (for example Plymouth Rock, Rhode Island Red, Wyandotte).
Like the down colour crosses, it must be in that order; it doesn’t work the other way around.
Leg colour
There are some breed crosses where the colour of the legs is linked to the sex of the offspring.
According to Katie Thear in “Incubation: a guide to hatching & rearing” (pp 73-75), there are dark-legged males and pale-legged female pairings that will produce light-legged cockerels and dark-legged pullets.
What about the commercial layers? Aren’t they sexlinked?
Yes. But we don’t know the precise recipe for their production.
We know that the brown layers hatch as buff/yellow pullets and white cockerels, maturing into brown-feathered hens and white-feathered roosters (where the boys slip through the sexing program). These are the main commercial layers available in Australia.
We can suspect that the white layers are feather-sexed, and the black layers may be the result of cuckoo breedings.
But we don’t know for sure.
However, Australia does have its own commercial breeders - Bond’s, Barter’s, and Wagners are the three main growers. They’re less intensively-bred, and tend not to have the same health issues at the overseas varieties. This is particularly because they are more likely to off the lay in winter, and to lay slightly fewer eggs overall even in their first year of laying.
And Australian supplier Bond has its crosses on its website. This is very nice of them!
They will, of course, also have worked very hard to select lines within their breeds to improve characteristics such as egglaying, feed efficiency, lack of broodiness, and so on. While anyone can replicate these specific crosses, they most probably won’t have the same efficiencies as those bred by the actual hatchery.
But we can at least see how the sex-linkages are likely to work.
Browns tend to have Rhode Island Red, and probably Rhode Island White, involved. The pullets will hatch with red/gold feathers and cockerels with white feathers. The hens become brown hens with white wing and tail feathers. There are other varieties that are brown-feathered with black highlights on neck and tail; I’m going to guess that some barred Rock is involved here, or maybe even Leghorn. There are a number of ways to produce sex-linked brown hens.
Whites almost certainly have white Leghorn involved, simply because Leghorns are the classic layer breed. The commercial cross would have pullets with long/irregular wingfeathers, and cockerels with short/regular length wingfeathers, growing into hens with white feathers and brown or black speckles through the feathers.
Blacks are variable. They can be RIR cockerel over Plymouth Rock hen, which will reliably produce pullets with black heads that grow into black hens with red chest/neck leakage. Note that this cross has no Australorp in it at all, even though everyone calls them “commercial Australorps”.
The Bond’s website says theirs are RIR roosters over Australorp hens; I can’t for the life of me see how that produces a sex-link cross, so it must be their own carefully-selected sex-linked line.
For more information
There are many, many resources out there on this topic. These are the ones that have specifically been mentioned or used in the production of these articles.
My other articles in the series
Part 1: Introduction (this article)
Discussions of actual sex-linked crosses
These are from the Australian Poultry by Backyard Poultry Facebook group.
Books and online articles
Backyard Poultry forums: sex-link cross breeds. The article that started it all, currently only available in the Web Archive.
Adelaide Chicken Sitting Services: Creating a Cross Breed.
Australian Poultry by Backyard Poultry: Sex-linked cross-breedings.
Backyard Poultry magazine: How to Sex Chicks: What Does and Doesn’t Work
Bond Backyard Layers: Our breeds
Kemp, Rick. Exhibition Poultry, pg 35-36.
Chickens in my garden: YouTube channel -
Chickens in my garden: Chicken Genetics 4 - sex-linked cross
Cluckin.net. Sexing chicks. 10 ways that work and 8 that do not.
Hendrix Genetics: Feather sexing in Day-Old chicks
Poultry Extension: Sexing Day-old Chicks
Poultry Keeper: Poultry Genetics: Black and White
Poultry Keeper: Sex-Linked Crosses and their Offspring
Thear, Katie. Incubation: a guide to hatching & rearing. pp 73-75. Broad Leys Publications, 2015.
University of Kentucky Department of Animal & Food Sciences: Sex-Linked Crosses