My 5 month old Boerboel is limping?

Being a boerboel (South african mastiff), he is very large for a puppy, but that is normal for his breed. He is about 70 Lbs. and right on track. This morning I noticed him limping and he didn't want to climb the stairs to come into the house after going potty. He sleeps with us in the bed and has plenty of room. I know being a puppy he is clumsy, but he hasn't fallen or hurt himself that I know of. Can it be just his leg is asleep or could it be something else?

I'm always worried when a giant breed puppy starts limping (I had an Irish wolfhound who had a problem with his back legs). I'd be either contacting the breeder, who should be thoroughly familiar with his line and problems that might crop up - maybe too much exercise, maybe the food, or something else. Or take him to his vet to be checked out.

Just a suggestion: Call you vet and ask him to explain Pano to you. Very common in large breed dogs of this age.