You CAN give it orally. It's seems just about as effective, maybe not quite as quick... and I'd give it for a minimum of 5 days.
Of course, it can be given IM injection, too... but DO keep in mind that it's meant to be injected into the muscle of a LARGE animal... it does cause some muscle damage, which can vary. The damage it may cause in a very large animal is insignificant due to the SIZE of the muscle/animal. There isn't as much muscle in a WHOLE chicken as there is in just a very small area on either of those other animals.
IF given in the muscle, don't go deep at all. AND, change injection site every time. The birds don't seem to react much when actually injected, but it does burn/sting very much, and I've had some act very, very tender at the injection site for a few days.
You can inject it sub-Q, too... and in the neck... but again, they can be sore. I had some that didn't want to move their neck, stood with their neck "in their shoulders" for a day starting the morning after the first injection sub-Q'd in the back of their neck...