Hello,
Well, that is great news he is eating vigorously right now, super!
I would start with 4-8mls, (depending on his body weight) daily, broken up into several feedings so he doesn't get overfull. How long have you had him for? How do his stools look? A good rule of thumb is usually .5ml per 50 kg of body weight, or 1ml per 100 kg. That is normally used to maintain body weight, so if he needs to gain weight, you can go as high as 1ml per 50 kg or 2ml per 100 kg.
Once he has had several normal looking stools with a good amount of soft urates included then you can increase some protein. That just ensures he is well
hydrated & his kidneys should be working pretty well. It is important for the kidneys because of his dehydration status it makes it harder on his system to break down uric acid being dehydrated.
I realize he is your neighbors, so is he getting any UVB lighting? How often are you giving him calcium? I just hope his jaw doesn't continue to deviate due to no UVB or calcium.
Keep us posted on him.
Tracie