Switching out Breeding roosters, from an American Bresse to a Cornish Cross

To order American Bresse chicks https://therecreationalhomestead.com Order a Surehatch incubator and other chicken supplies. Use promo code RecHomestead https://indivfarmsupply.com/ Get a discount on anything on the site and it also gives us a kickback!Thank you!!! If you are in south west Michigan check out our herd share and pasture raised meats https://therecreationalhomestead.com I am trying to develop my own breed of chicken by crossing the American Bresse ( the best tasting chicken in the world that also lays 250 eggs per year) with the Cornish Cross (the fastest growing chicken with the best feed conversion) to do this I slowed the growth of 3 Cornish Roaster roosters so they would be at a healthier weight for breeding and then put them in with my American Bresse hens. Keep in mine when switching out roosters how long it take for the old rooster to stop fertilizing eggs and how long it take for the new rooster to start fertilizing eggs