
Naturediet feeding guides are notoriously on the high side and are the recommended
maximum that should be fed daily. You need to use your knowledge of your dog to determine how much to feed. If he seems stuffed after his meal then cut back a bit (many pups are greedy and would eat til they burst). If he still seems hungry and is scavaging for food, then increase it a bit. It's not an exact science as every dog is different, has different activity levels etc. You also need to adjust amounts to take into account any extras the dog might get throughout the day in treats etc. If I had fed my pup the amount recommended by Naturediet, she'd have been a right pudding. I started with about half the recommended amount and worked from there.
You'll know if he's getting enough by feeling his ribcage. If the ribs are nicely covered but you can still feel them easily then he's about right. If you can see the ribs easily then he's too skinny and needs a bit more. If you need to dig around to even find his ribcage, then you need to cut his food back a bit. It is better for dogs to be on the lean side without being to skinny. You see far too many fat dogs waddling around these days (almost every CKCS I see is way too heavy) and there is a danger that people will begin to think that is what a dog should look like :(
HTH