Crushed shells will not encourage egg eating. Did that for many years. Lack of protein in the diet would be a more likely cause. As far as layer rations, my roosters eat what my hens eat. My two longest lived roosters so far were a Delaware and a Blue Orpington, both ate layer feed all their lives after chick starter. They lived 6 yrs 7 mos and 5 yrs 8 mos, respectively. Neither had issues with the calcium. I have had a few other roosters, currently my oldest two are Belgian D'Anvers (very small bantams) who are 6 yrs and 5 yrs old. Neither has issues with the layer feed. When I had a rooster who was crippled and lived in his own cage and had food to himself, he ate the 12 grain scratch mix, but all roosters I've had here for the past 12 years have eaten the layer feed with no known ill effects. I am not sure when you'd see those unless the rooster was slightly unhealthy in the first place and the calcium had an adverse effect, but I have never noticed anything.