I've heard that bears don't come near horses.  Not sure how much I believe that.

Dogs are an iffy situation.  Depends on the bear.  Depends on the dog.  I've heard anecdotes of dogs chasing bears away and dogs leading bears back to camp.

My favourite bear/dog story can be found on myccr, if it's still there.  Going back near a decade.  Samsman is the poster.  Sam is the dog.  Here's a quick synopsis, but the full read is much better.  Bear comes charging down the trail.  Sam (a bull terrier type dog less than 1 foot tall at the shoulder) charges the bear.  Bear attacks Sam.  Samsman attacks bear with a knife. 

Highlight to the yellow to see the outcome.  Better yet, track down the myccr thread and read the full account.  Bear dies.  Sam & man are ok.