You are correct in thinking it will hurt the rooster over a longer period of time. But what is a long period of time? 50 lbs last my few silkies a couple of months or longer and that would be too long. If your chickens are free range then they are getting something other than just the mash and the laying mash is not likely to hurt your rooster. But as the only source of food-I am not sure just how long it takes to effect body systems. Our pet red squirrel is affected by calcium overdose within a few weeks. Be careful.