Now that is a VERY DANGEROUS thing to do. The broilers are not so aggressive but the layers and similiar birds are. I have done that very thing in the past. In fact if you read the chicken manuals by the experts they do not recommend it at all. I have personally seen a large hen peck the guts out of a younger hen. Very dangerous. I suggest you download the Ross 308 Parent Stock manual and see what they have to say. Check out the LOhmanns Parent Stock manual as well. Careful. My advice with all my experience is do not evens try to attempt it. The bigger birds will KILL the smaller ones.
I agree. I had some meaties in with layers of the same age and as soon as the meaties were about twice their size they started pecking the smaller birds. I didn't let it get far enough to loose any but it could very easily have gone that way if I hadn't seperated them.