I have a flock of 21 chickens. I have 4 that are coughing(?). They have a bit of a runny nose/beak and one has watery eyes. I got some antibiotics from the vet. I am treating the individual chickens with a syringe. However, this "cold" seems to clear with one chicken and then pop up in another. What can I use to treat the whole flock at once so I'm not spending too much time driving back and forth to the vet for more stuff? My feed store guy (also raises chickens) suggested Corid. Is that good? Will it work? I need some help here.