dog nipping

Question
i have a 12 1/2  yr old chocolate lab,who up until just recently was a wonderful dog,now she bites tires and grabs and nips men's legs but not all the time,can't exercise her alot because she has bad arthritis in back legs but does walk each day but not far.she's normally a very sweet dog and has never had a prey drive problem,is this what it is and how can i help her.

Answer
Often when an older dog develops a problem behavior there is a physical cause behind it.  I would suggest a vet visit explaining the problem.  The vets have some very good pain remedies.  It is possible somehow she is associating her pain with tires and men.  It is was some sort of a bad experience, it will be harder to work out.  I would schedule a vet appointment.  Be thinking of any possible incidences and get back with me if the vet doesn't solve the problem.  

You might try having men offer her treats.