
I also feed AG puppy, however have a large breed. The recommended daily amount for me is between 400-800grams (the top end of that seems a lot to me) so maybe just check the recommended daily amount for your pups weight... I am guessing 200-500grams of AG/day? Also, if you can, check with your breeder and see what they recommend and also what they think the ideal weight for your boy at his age is.
As mentioned before, it's normal for pups to pick up all sorts of different things, the more disgusting the more they like it! However if he is actually searching out grass, leaves, sticks and just munching them down as though they were food, I might be inclined to bump up his food a bit.
If you still have no joy, maybe speak to your vet and see what they think. No doubt they will advise you start feeing a different brand (the one they promote) - but if they confirm he is in good shape/weight then maybe he just loves his food!!
I am sure there are other Staff owners who will pitch in some ideas too... best of luck!