How quickly do American Mastiff puppies grow?

American Mastiff puppies grow very quickly.  You will notice that they eat and then sleep A LOT.  On average, puppies gain between three and five pounds per week for their first eight months or so.  Because they can't possibly eat enough at one sitting to sustain themselves for more than one hour at a time, it is recommended that they be free-fed so they can eat throughout the day. 

Because American Mastiff puppies grow so very quickly, great care must be taken to ensure that their joints and bones are protected from injury.  American Mastiffs puppies must not be over-exercised. This means no jumping off anything higher than 12 inches or so, no major "rough-housing" with people or other pets, and no excessive running or quick turns. 

It is a good idea to train your American Mastiff puppy while relatively young to use a ramp to get in and out of your vehicle.  Once they become too large to safely lift, it will become potentially dangerous for both you and your American Mastiff to try to lift him/her into your vehicle.   

After the first year, their growth rate begins to slow down.  You will notice growth spurts in your American Mastiff by the sudden increase in appetite.  American Mastiffs grow "up" (tall) for the first two years and "out" (fill out) for the next two years.  American Mastiffs are not fully grown until four years of age.