[ChrisD]

Thanks for the replies. He will not be going on trail rides with us until he is at least 18 mo and his OB is solid, I agree you have little control when on horseback, but that is the long term goal.
Right now we are working on manners around the horses and he gives them a wide berth. Our friends Weimeraner pup had his foot stepped on 2 weeks ago, not pretty, so he is closely supervised around the horses.

The exercise amounts I was looking for were regarding walks/play with me, not trail rides, just some general amounts while he is growing.