The Isa Browns is a production breed and will out lay the Barred Rocks in the first 1 1/2 to 2 years years and then slack off, but still lay for several years, just not near as good. Production breeds peak in a shorter period then heritage breeds. The Barred Rocks being a heritage breed, will lay good for a about 2 1/2 to 3 years before they slack off, but may lay eggs for 5 or 6 years. It all depends on the breed. I have hens that are still laying eggs at 7. Not many, but an egg here and there. It all comes down to do you want your eggs all up front with a short laying cycle, or a heritage breed that won't burn out and lay eggs longer.