It might be a respiratory virus such as infectious bronchitis, or possibly a mycoplasma (MG) infection. Usually many chickens will become affected at the same time with bronchitis. You may want to separate him in a warm place to observe him for a day or two. Here is a good link to read about the common diseases: http://edis.ifas.ufl.edu/ps044
- Monkey Lookout
Viruses won't respond to antibiotics, but if there are any bacterial infections or secondary infections, those can respond. Typical feed store antibiotics added to the water for respiratory diseases are Tylan, oxytetracycline, Duramycin 10, and Gallimycin (erythromycin.) Those are added to the water, and Tylan 50 injectable can be given orally to just the sick rooster. For a 5 lb bird, give 1 ml orally twice a day for 5 days. For a chick give 1/4 ml, and for a bird under 5 lb, give 1/2 ml.
Yes, and that is the key, is getting them through it without having it morph into pneumonia and secondary bacterial infections. As long as it's just clear runny nose and sneezing you can probably hold off an antibiotics. If you start to hear coughing, rattling or wheezing breathing then you need to start the meds. They also need to be kept warm while they are sick.
That is true for the sick ones showing symptoms. They can get chilled easily and have trouble maintaining temperature. Be very careful with heat lamps, especially the 250 watt ones. Make sure it is secure. Sometimes it can be easier to bring in one sick bird inside a house or heated basement.