I have an 11 year old Rottweiler, named Belle, and recently she’s been quite grumpy. Normally she is pretty mellow and puts up with quite a bit. However, as of late, she’s been growling at the cats, and even at my smaller dog, Trixie.

Belle does have arthritis, but she’s been put on Deramaxx and morphine for the pain. What could be causing her to be so grumpy?