I agree with Chris, and would just like to add that you also should just give a small sprinkle of mixed corn as a treat occasionally, and as their main diet they should have whatever complete pellets are appropriate for game birds. (What kind of game birds for you have?) Corn, scraps and fruit give a very unbalanced diet for any kind of poultry and the maize in mixed corn is also very fattening, sometimes even with fatal consequences when the fat obstructs the hens' ovaries. As well as the danger of sour crop from human scraps, they may contain what to birds are high levels of fat, sugar and salt, all potentially bad for birds, though they do love what to them is junk food. A good specialist brand of pellets will provide all the vitamins and minerals they need, and a deficiency might possibly be the cause of their present problems. I don't know whether layers pellets for chickens would be better for them, but I expect your local agricultural store could advise, or someone on here will have the answer.