No 9month old pup should not be pulling much weight ESPECIALLY not a 9 month old mastiff puppy ;) At the kennel, we dont start training pupsuntil they are about 8 months old BUT they are put in large teams so they really arnt pulling much weight at all. By the time time they start figuring themselves out in a large team and really know what is expected of them and how to do it properly so they "graduate" to smaller teams, they are a year old if not more. Mastiffs shouldnt be expected to pull weight until at least a year since they are so slow to mature. Too much weight too early is hard on the developing joints and could lead to problems later on that may not have otherwise occured...