" A brother sister mating or two..."
Is this meant as more than one cross between pairs of siblings in the same year? Or crossing brothers with sisters for more than one year. Would it be advisable to do it for more than one year? I would worry that they would become too close. My feather pen though, had a very distantly related male so it might be safe to try it. I don't want to lose size. I've got good size in my flock but last breeding season I had to use a male that had the bantam gene over my large fowl females and apparently he will pass that gene to all of his offspring. Getting that out of my large fowl flock will be an interesting challenge. I also had a male with no bantam gene so I have choices that I need to remember when it comes time to choose. Luckily, the no bantam gene male with the females I chose for him have given me some really really nice looking offspring. I can hardly wait for them to mature and fill out!
Unless there is a concern otherwise I would not be afraid of a brother and sister mating in a side pen. That is if you are trying to fix a trait, and if two siblings had what I wanted, I would use them together. There would be no faster way to fix it.
By two, I would mean in another generation if necessary, but once would generally be enough if it was followed by a mother x son, father x daughter that all had what you were looing for.
Keep in mind, I am discussing the topic of breeding especially tight for a reason. A single brother sister mating would not hurt you unless they already had problems or were already too closely bred. This is a hypothetical temporary pen where you will end up breeding back away and will have an increase of vigor in the initial outcross over than would you would have had otherwise.
It would not be advisable to make a practice of this in a family that you would continue with. It could however be a tool to fix something so that it had more influence when introduced to a family.
My thinking is based on the idea that not all traits are simple recessive or dominate traits. Some characteristics are a compilation of genes that have been accumulated by selection. A bird that has this characteristic(s) that comes from a family that is strong on this point will be more influential. In a rare breed that has no families strong on a particular point, possibly we could make a temporary one faster by this idea.
It is just a theory, but it is not without it's precedence. The commercial industry is built on a similar philosophy. To accumulate a compilation of genes related to production in a tightly bred group with the goal of crossing with another to gain the added benefit of hybrid vigor. Uniformity requires getting close, and close is more influential than random. We could get closer faster by incorporating a brother x sister mating into a side pen that is a terminal line anyways.
They say that it takes 5 years (generations) to breed back up to standard size. I have never done it myself. It sounds like that male may already be up to size.
I would like to see pictures of your birds when you are ready. I will send you a couple pictures of where I ended up this year.
