I have 12 chickens that are approx. 11 weeks old. they have been on purina mills start and grow the entire time (medicated w/ amprolium, 18% protien) I was getting low on feed, and wasn't going to the town where it is sold, so I went to the local co-op and got some starter/grower. it has the amprolium and 16% protein, but it also has bacitracin methylene disalicylate in it. should I give this to my chickens or just take it back and make a special trip into the other town to get the other? it says start at hatching and continue until laying age, would it hurt to start it now?