You probably notice that Lucah goes through lean and not-so-lean stages since he is growing so quickly. If he is looking too lean and you easily see his ribs, then give him more food! He's a big pup, he'll find places to put that extra food. I don't remember what amounts we fed Nola as a little pup, but when we stopped feeding Nola kibble (about 8-10 months of age) he was up to about 8-10 cups a day.
Is Cub a puppy formula? You need to be careful with puppy formulas and giant breeds. If they are getting more than about 24% protein, that is too much. The advise we were given when Nola was a puppy was to get off puppy food immediately and go directly to adult food. The protein level in adult formula is lower than puppy formula. A puppy can grow too quickly and wind up with joint problems.
Good luck