exercising and suppliments

Optimus- Prime

Barked: Tue Dec 4, '12 9:14am PST 
Optimus prime is 6 months old now and about 80lbs. I have been taking him on walks a lot. I stated to up the distnces and making the terrain more difficult about 2 months ago.

My question is with saint Bernard being known for hip problems, what it pushing him too far?
I took him to the mountains last week and we did 14 miles. That was about 8 more miles than he has ever done. He seemed fine just exhausted.

Also I shoulda like to know if it's to soon to get him to carry his own pack, not too much weight just his water and food.

Last question is about supplements. Is it ever too soon to get him started on joint support and other multi vitamins?