My chicks that are in question here are 4 wks. old now and I thought they were over the infectious coryza. I switched their starter food this morning to the Dumor brand chick starter/grower, which is bigger than the co-op chick starter I was feeding them. I didn't think there would be any issue here because it is supposed to be chick starter. Well, I have gone to check on them and 2 of them looked like they were gasping for air. I opened one of the BR's beaks and noticed that it had food stuck in the back of its throat. One of the d'Uccles is doing the same thing. I managed to get d'Uccle to throw up (don't ask how!) and he still seems to be gasping a bit. There also seems to be a lot of mucus in their mouths and throats. I am at my whit's end with these chickens! I feel like we get one problem taken care of and now another pops up. Please HELP!!!