A lot depends on diet. If you are feeding a laying ration to your whole flock, the roosters may not continue to be fertile past three years. To much calcium is bad for a rooster and can cause health problems. Many people who raise show quality flocks use a flock raiser ration and supplement with oyster shell free choice. The chickens will eat what they need. I have never seen any of my roosters dip into the oyster shell. I have found the Flock Raising ration to be hard to find around here so I use the unmedicated starter grower and mix in a a 16 percent scratch grain feed.