My RIRS roo is twice the size of his hens..they are the same age 5mo. I also have cemanis..and thier roo is twice thier size. Roos are naturally bigger. I think they should be fine. Often..roos will have a favorite hen..u can usually tell who she is because she will be missing feathers. U have a pretty good amount of girls for him..so I wouldn't worry...they will keep him busy. Not all roos are rough on thier hens..just depends on the roo..Thank you for the welcome. I separated him from the rest because of his size; 12-14#. 8 of the girls are 20 week old pullets and the rest are smaller ISA browns. I didn't know if his mating would hurt them.
