fcsantos..... How much protein is it in the food you are giving? I was assuming your dog is an OEM based on the weight lol.... The mastiffs and even the danes and other giant breeds for that matter, sometimes grow a bit too fast, not overweight just grow too fast. And sometimes knockel over a bit. We have never had Galahad on over 21% protein, and when he was about hmmm 4 and a half months I think, he started to knockel a bit and we decided to bring him down on no more than 17-19%. I agree with Rachel that giant breeds do very well on an all stage dog food even as puppies, actaully better most times, since the protein is often lower.
The amount you feed sound like a very "normal" amount. since it is a giant breed puppy you have you might want to concider adding some kind of joint supplement and antioxidants, like someone posted here 3 months is a bit fluent, it is easier to compare if you use weeks, just because 2 weeks more or less is making such a big difference. But if Zoe is actually 3 months = 12-13 weeks she is definately not on the small side. Also matters the size the dogs mostly end up as for that particular bloodline, so how big is her mom and dad?
There are many good food out there, personally I prefer the holistic kinds, they are a little more expensive than some but you get "real" food rather than fillers and can most often lower the daily intake.
Good Luck and keep us posted
Marit