For chickens Plumbs Veterinary Handbook says that 10-40mg per Kg 2-3 times a day is acceptable. That is 5-10mg per pound. In each Tylan 50, each ml equals 50mg. Some people give it orally if they are not comfortable with injections. It is thick, so if giving injections into the muscle, I would use a 22 gauge. If givng it orally, I would use a 20 gauge or even an 18 gauge to withdraw it from the vial. Then remove the needle to give it orally. Do you know how much your hen weighs? If you don't have a kitchen or postal scale, you can hold them while weighing yourself, then subtact your weight to get  rough estimate. For a 5 pound chicken I would give 1 ml twice a day at least, and increase it by 0.50 ml for every 2.5 pounds.