Make sure you give him enough. Do you have Tylan 50 or Tylan 200?
Note that Tylan needs to be given several times a day when used on poultry. Since it can cause severe injection site necrosis I recommend giving it orally 3-4 times a day.
There is one vet that says to give Tylan 50 at 0.2 ml per pound of body weight every 6-8 hours. If using Tylan 200 that would be 0.05 ml every 6-8 hours.
Elanco, the makers of Tylan, say when using Tylan Soluble Powder the turkey dose is 60 mg per pound per day and that is what I would do if treating one of mine.
These are the 60 mg per pound numbers I would go by if treating mine:
Tylan 200 - 0.1 ml per pound three times a day
Tylan 200 - 0.075 ml per pound four times a day
Tylan 50 - 0.4 ml per pound three times a day
Tylan 50 - 0.3 ml per pound four times a day
Does that help?