You should always draw back on needles on any injection, subcutaneous, IM, or IV, just to make sure you are not in a vein, since some drugs are not supposed to be given in the vein. Of course, that is how you tell if you are in a vein giving something IV, or if the IV is still working and not infiltrated. Most injections on chickens should be given into the breast muscle only 1/4 inch deep. Using the shortest needl possible is good, but it needs to be large enough gauge for the medicine (or thick medicine) to go through.
Ahh, yes, now I see what you meant.... excellent explanation that will help many, thanks.I meant that when giving an IM injection you should check for blood. IMs should not be given in veins.
My vet recommends giving antibiotics two days past cessation of symptoms.