It started with one hen a couple weeks ago who would do what sounded like a hiccup or at times, and extended crow. Then, I noticed last week a different hen with what sounded like a congested chest, bubbled type sounds when breathing and now yesterday have 3 hens and 1 turkey with the congested sounds. From reading other posts on here, it sounds like it might be CRD or maybe worms could be causing it. I initially thought my first hen had crop issues so I gave her olive oil and massaged the crop for two days but it did not seem to help. After the other hens and turkey got the congestion sound (my first hen does not have that, just still the long crow), I read some more and thought maybe the worms or CRD. I cannot see any worms anywhere by their run. They free range all day and go in by themselves to roost at night before I close them safely in their run/roost which is about 17 feet wide and 20 feet long (not counting their actual 10x12 house). I bought some Duramycin-10 (tetracycline hydrochloride soluble powder) when I was at the local farm store the other day because it says it treats CRD in chickens and turkeys but I have not seen anyone else post on here that they have used that. I thought I would put it into the drinking water for all my birds (41 of them -31 chickens and ten turkeys) because I am afraid it may be spreading. I assume I should treat all of my birds. Should I try de-worming at the same time I try the medicine for the CRD or would that hurt them somehow? For the Duramycin, how do I give the dosage? Based on the directions, I think it should be about 1 1/2 teaspoons per gallon of water but by the instructions, it looks like I add it to the water and just let them drink it as needed. Does this sound correct to just let them have as much of the antibiotic as they can drink? Some of my chickens are only 3 months old and I don't want to overdose them-none of them are showing the symptoms, only my 18 month old chickens are.