"my roosters eat layer feed and they haven't started laying eggs "
ChicknGurl: first of all, roosters DONT lay eggs! Second of all, even though most people feed roosters layer feed, it is not the proper diet for them. They make rooster feed with the proper nutrition for them. And as far as cats go....they have nothing to do with chickens. If someone wants to change between feeds, they do not need to mix it with the old food to prevent stomach problems.
Jeaucamom: I applaud all your efforts with everything you have done so far. Just please be careful when asking for help that you research the treatments you are given, please just dont go 'do it' to your chicken because someone says to. Some people dont know and are guessing, however, there are some very knowledgable people on here that give great advice, you just need to know which ones these are. I dont mean to put down any person who means well and is just trying to help, I 'm just saying, be careful with all the different 'solutions' that all the different people come up with.
Dlhunicorn posted a great article about the sulmet, if you have followed the directions on administering this drug and it has been the proper amount of days, take her off of it. She can be fed layer feed at anytime you want to give it to her. It is not going to hurt her if she is not on layer feed and happens to lay an egg. As far as the oyster shell, if when she starts to lay eggs again, you find the shells are very thin, then supply the oyster shell. If she never has access to outside, then you can add grit to the food.
Best of luck to you.