I am just not following the reasoning on this. How many eggs are you going to hatch? Personally, while all the sperm of one rooster may not be perfectly cleared out, adding the other rooster will get his share in. It is not that you don't want chicks from both roosters. And it is not like the sperm will mix, or kill off the other. It will just be luck who's sperm gets it done. And while you might get considerably more of one rooster's chicks than the other, I don't think you will.
Really I think it would be very upsetting to your hens to do the flipping out of a rooster, and adding another rooster, and that WILL effect fertility. You could just put 3 of each kind hen in with one rooster, 6 hen, 3 BO and 3 barred rocks, and the same with the other rooster. And you would have both crosses done without flipping roosters at all. A lot less commotion.
Perhaps there is something special about the 12 girls, that you want each hen covered by each rooster? But truthfully, it would be a lot less stressful on your birds, and a lot easier to set up, if you just create a breeding pen, with a mixed breed hen flock and single rooster. In 2 days, there will be as many eggs as 12 will lay in one day. Two days is nothing when considering fertility. Anything under 10 days is pretty reasonable, unless they get frozen or something.
Mrs K
Really I think it would be very upsetting to your hens to do the flipping out of a rooster, and adding another rooster, and that WILL effect fertility. You could just put 3 of each kind hen in with one rooster, 6 hen, 3 BO and 3 barred rocks, and the same with the other rooster. And you would have both crosses done without flipping roosters at all. A lot less commotion.
Perhaps there is something special about the 12 girls, that you want each hen covered by each rooster? But truthfully, it would be a lot less stressful on your birds, and a lot easier to set up, if you just create a breeding pen, with a mixed breed hen flock and single rooster. In 2 days, there will be as many eggs as 12 will lay in one day. Two days is nothing when considering fertility. Anything under 10 days is pretty reasonable, unless they get frozen or something.
Mrs K