#1 Why would one wish to breed sex link birds rather than purebred birds? Aside from the obvious advantage of being able to easily sex them at birth?
There is the obvious one, commercial egg laying operations do not want to feed cockerels to an age that they can tell the sex. Even a very unskilled low-wage person can separate sex linked male and female chicks at hatch.
Many people with a small backyard flock do not want males or cannot have them. Getting sex-linked pullets gets around that problem. Occasionally someone may want only males so they can raise them to butcher size. Some people just think it is neat or fun. If you are hatching chicks to sell, being sure which chicks are pullets can make that a lot easier and you can probably charge more per chick. I’m sure there are many other reasons.
#2 Is there a list of pros and cons to having sex link birds?
Other than being able to sex them at hatch, not really. There are a lot of misconceptions about that. Some people like to think that there are magical properties associated with sex links. There are not. One huge cause of confusion is that our sex links we can get here in the States from the hatcheries we normally use can be two different types. One type is based on the commercial sex-linked hybrid layers. There are egg laying machines. It doesn’t have anything to do with them being sex links, it has to do with being bred to lay a lot of fairly large eggs efficiently. The other type of sex links offered are crosses between standard dual purpose breeds. These sex links are like their parents, bigger and still good egg layers but not as good at egg laying as the hybrids especially bred to lay a lot of eggs.
I’ll give an example. If you cross a Buff Orpington rooster over a Silver Laced Wyandotte hen you will get a red sex link. The pullets and cockerels will have the characteristics of their parents. If the parents lay well, the pullets will lay well. If the parents make good meat birds the cockerels will make good meat birds. If you cross a Silver Laced Wyandotte rooster form that same SLW flock over a Buff Orp hen from that same BO flock, you will not get a sex linked chick but those chicks will have the same production characteristics as their sex linked cousins.
#3 I was reading that crossing two sex link birds does not lead to the babies being sex link chicks. In this case what are the babies, just mutts?
Correct, you cannot make sex links from sex linked chicks. To make sex links the parents have to be set up a specific way genetically. Once you make sex links you have lost that set-up in the chicks. Since sex links are crosses you can call them mutts if you wish. Their offspring are certainly mixes.
If you have not yet seen it, you might want to read the first post in this thread. It takes some study to understand but Tim gives a good scientific explanation in how you get sex links. He also gives charts that you can use to determine if certain breeds can be used to make sex links. Those chrts are not all-inclusive, there are combinations that work that are not in those charts, but they do cover a lot of common breeds and colors.
Tadkerson’s Sex Link Thread
#4 I was reading another thread, sex link information, and saw a list of chickens that will produce Red or Black sex link chicks but I don't know if that was complete so I was wondering if a sex link can be made from breeding a Buff Orpington roster over a Silver Laced Wyandotte hen? What about a RIR roster over a Dominique hen? I ask because between my mother and I these are the breeds we have and are curious about hatching some chicks in the future and was weighing the pros and cons of keeping them separate or mixing them.
A Buff Orpington rooster has gold, a SLW hen has silver, and you can see the reddish and yellow down in the chicks. You will get a red sex link.
A RIR rooster does not have barring, a Dominique hen does have barring. The black in the Dominique hen will override the red in the RIR rooster so you will be able to see the spot. You will get a black sex linked chick.