I wouldn't feel comfortable just me around a pitbull at any time let alone leave a small yorkie in their vicinity. It only takes a second for them to grab and kill a small animal. No dog is going to be in good humor 100% of the time so who knows when a pitbull could turn on you and especially a small, active yorkie?
I don't know one pitbull owner who doesn't think their pitbull is "safe" and would never attack anyone or anything. Right. You can watch the news almost daily with owners of pitbulls getting attack and they're family members.
Could you sleep at night? I know I never would if one of my yorkies was anywhere near a pitbull.
__________________  Toby, Shelby Rose, Kasey & Oliver's Mom |