I had to get 9 of my BO roos butchered at 5 months because they were tearing up my hens. Now I have 1 BO roo, and 1 RIR roo. They free-range and breed with both other breeds. What's happened is that now I have mixed chicks and some purebred ones, which is fine for my purposes. But I like to keep at least some purebreds around in case I want to make sure I get purebreds.
