My youngest will be 20 weeks old sunday and I want to let them in with the big birds this weekend when I'll be home to supervise. I have almost a whole bag of purina medicated grower/starter feed left. Can I mix it in with the layer food and let them all eat it without causing any of them any problems? Also if I have hens not laying because they are too old will the calcium in layer food hurt them? I have some hens from people giving them away and no clue of their ages, but am letting them live until they die from old age.... I don't know who is laying and who isn't.