Good comments above, but with any heavy breed need to watch they don`t get too much, what i call heavy exercise out with the bike etc, as the dogs growth plates may not have finished closing over you could do some damage for later on that cant be put right, mooching round the farm is one thing but too much sustained hard running is not so good. My 10mnth old bull/fell/grey is getting similar exercise to your minus the bike work, hes fit as f**k, but i would like to give him another 5-6mnths before hammering him! It is hard coz hes keen to do more, just my experience