Dane not eating enough

Question
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Followup To
Question -
I have a 4.5yr old black great dane.  He has always been a light eater and has not been very heavy.  We liked the fact that he was thin since it is better to have him lean when growing, but now he is almost two thin.  He is abmormally tall and only weighs 128 lbs.  He has been to the vet serveral times and nothing can be found.  He is so skinny that we have had animal control called--but he is still very healty and active.  They just laughed that someone called.  I still feel he should be somewhat heavier but he will only eat 5 to 6 cups of food per day.  He has unlimited access to his food but just chooses not to eat.  However if he smells or sees people food he acts as if he is starving.  He has been this way for almost his whole life.  Is there anything I can do?
Thank You, Ron Swiger
Answer -
What do you feed him on?

When do you feed him?

What is his exercise regime?

We feed a good 20% protein dried food containing oil, mixed with raw minced tripe.  We wet the food with gravy made from OXO, Bovril or Gravy Ganules.  Try mixing the dry food with some very cheap, therefore smelly, dog food mixed with hot water to make the gravy. (Make sure it is cool first.)

Don't feed immediately after exercise, let him cool down for 20 minutes.  Don't take him more than 1/2 mile, the more you exercise the thinner he will be if he doesn't eat.

**We feed him Pro Plan giant breed.  He eats from a raised bowl and has food left in his bowl constantly.  Everytime it is low we fill it up.  As far as exercise he gets a 15min walk daily.  I haven't tried the gravey idea and probably will now.  
Thanks, Ron Swiger


Answer
You should feed two meals a day at about 08:00 and 18:00 or whatever fits your lfe style.  Snacking through the day spoils his appetite.  If he leaves some take it away he will soon get the idea that he eats when you tell him and there is nothing, I MEAN NOTHING, in between.  No treats or snacks.  Its like children, if you let them eat treats between meals they will not eat their proper meal.  If you are going to let him snack constantly feed him fattening foods like crisps, chocolate, burgers, fries etc.