I have noticed that a lot of folks will run several roos with their hens. I have heard of very few problems with flocks using this method of breeding. I think the biggest problem would arise to someone trying to improve a flock by breeding out imperfections. If you dont know which roo is the daddy or which hen is the mother, it would be hard to guess which bird is throwing the imperfections you wish to get rid of. I only run one roo with just a few hens in each coop. While i am just getting into raiseing buckeyes, I feel being able to know without a doubt which roo and small group of hens are the parents of the chicks, will enable me to cull much more efficiently. This method also allows me the opportunity to swap roos among the different flocks to see which roo/hen combinations produces the best offspring. It also allows me to basicly keep 4 flocks for the price of two. I also run extra roos with other breeds of birds until the time that they are needed. If needed, I can pretty much guarantee that there are no brother to sister, father to daughter, mother to son breeding taking place in my pens. ( Lots of cousings breeding). Notice, I said "if needed", there is a lot to be said for line breeding and it is a common practice to breed father to daughter/grandaughter and mother to sons/grandsons. I am sure someone could also make a good argument for breeding brother to sister, altho I try not to with my birds.