I expect people who actually show their birds will have extra advice, but for any birds I would cut out the old bread completely, also any kitchen scraps apart from the fruit and veg. If they are eating an age-appropriate layers or growers feed and are in good health, not moulting, and not in the middle of winter, they shouldn't need any supplements as all the vitamins and minerals they need will be present in their pellets. If you cut out the bread, which is nutritionally useless, they will have more room and appetite for the good stuff, especially the growers.