for a giant-breed puppy, it’s VERY GOOD to be able to see a hint of bones. Skinny is best for those dogs. You need to be very cautious about stimulating growth of these giant dogs through adding foods willy-nilly.
Think of some skinny teenage boys you see- nothing but skin and bones. It’s normal during certain stages of growth for young animals to look thin.
That said, why did you select that particular food? the calcium may be too high for a giant-breed puppy (it says it’s not less than 1.2%- 1.2% is ok, but if it’s much higher than 1.2% it could cause some real problems).
The protein is barely high enough at 27%. It is also a fairly low calorie per cup food at only 400 kcal/cup.
If you’re concerned, your best best is to switch to a large-breed puppy food with more calories per cup and a known proper calcium level.
For example, look at Orijen large-breed puppy food. It provides a maximum amount of calcium (1.2 to 1.5%), necessary for proper bone growth in puppies- too high, you get serious problems.
It also has a more reasonable level of protein at 36%, and it has 456 kcal per cup so you’d feed less or feed the same and put weight on the dog.
Course you’d probably go broke trying to feed Orijen to a growing mastiff.