hi , i would not be overly worried sometimes its quite beneficial to keep growing pups lean rather than obese, that way joints are less likely damaged. not that pictures are perfect tool to use but his bone size is not massive, thats to say he probably wont make a huge specimen, as previous posters have noted they do grow at awkward stages and its always best to make the frame first then hang the meat as a farmer friend remarks.
is he kc registered ? there have been a lot of reputed full mastiff litters advertised on the internet in uk but the parents were crosses or extremely poor examples and should never been bred, during the period of your dogs birth only 5 litters were registered with the kc and only 3 apricot dog puppies out of 2 litters , both from very successful show kennels.
what certainly would not have helped your pup is the poor nutrition in his formative weeks, wagg dog food is definately not the food for giant breed pups , but atleast you have got him on the better stuff now, my boy was on r/c for his first year (70kg @8 mths) then moved over to raw feeding as was my bitch , at 3 yrs theres still bit more scope for size although not height at 32 in he is just above average for most uk bred dogs and his present weight is 96 kgs
certain mastiff bloodlines do mature very slowly and pups can look like dane crosses for over 18 mths then they start to beef up and can be considered not finished till around 3/4yrs and what ive noticed is to get a good idea of the finished dog look at the grand parents your see more of them in your dog than mum or dad .
some of my boy from 4 mth to 2 yrs
