You should really only start to do distance when the Rottie is older than 2 years,, its bad for joint since the grow up to 2 years but you will know i see you have Rotties aswell. the max we have done was a 18km but that was too far If you do 2 or 3km runs say twice a week he can do a qucker 5km and a easy 8km would not do more than that if the dog is not super fit, we are runners and they spend a lot of time on the trails with us. when fit , 5km and no more would be safe, also make sure all xrays are done and you know there is no problems that you dont know of Give them little water not too muck straigh after that and leave it a good 30min before you feed them
