You need to give these birds four drops of POLYVISOL Enfamil formulation into their beaks for a week immediately. This will take care of the most common deficiencies especially vit A which is commonly present with respiratory ailments.
They sound really too ill for terramycin to be effective...I am posting here below instructions for the use of tylan50 (injectible) ... this will allow you to give electrolytes/vit in the waterer which is necessary for all your birds that are panting (which in itself will induce a condition called acidosis which recquires electrolytes > you can get the electrolytes at your feed store and if the sotre does not have the tylan50 injectible then you can purchase that and the syringe/needles ata place like JEFFERS)
http://www.afn.org/~poultry/newsletr/1996/psep96.pdf
Chicken Medications
by Dr. James Barton and Clarence Gillihan
(excerpt)
".....Bacterial Diseases:
Purchase a bottle of Tylan 50 and several 3cc
syringes with 25 to 30 gauge 1/2" needles. Give yourhen 1 to 1 1/2 cc. of Tylan under the skin of the neck .........Continue daily injections for three days but not more than five. Withdrawal time is one month...... it is very good against Mycoplasma bacteria which is responsible for some respiratory diseases.
To inject Tylan 50, pull the hens feathers back
to reveal the skin on base of the the neck on her back.
Lift the skin up and insert the needle gentlty but firmly into the skin just far enough to allow the Tylan to be injected. You will be able to feel it. Be careful that you do not inject yourself. Make certain that you do not push the needle through the skin and out again not injecting
at all...........................
Because Tylan is so powerful, it is recommended
that you purchase some Beneficial Bird Bacteria
and feed it to your chicken after she recovers.
Tylan wipes out all the benficial bacteria that is normally present in a chickens digestive system. Also, Tylan can kill skin cells near the site of the injection so you should not use anything stronger than Tylan 50 - a stronger variety, Tylan-200 is also available at your local feed store, but this will likely do more harm than good.
When purchasing syringes, get them from a
local drug store. The 'human' grade needles are a little sharper than the vetrinary grade. The cost is about the same and your hen will thank you...."