Feel free to post other links. These are just starters:

http://www.vet.cornell.edu/pain/

"Pain management in animals is now recognized as an integral aspect of veterinary practice that offers many advantages to patients."

http://www.caberfeidh.com/Pain1.htm
http://www.caberfeidh.com/Pain2.htm
http://www.caberfeidh.com/Pain3.htm

paige is now on Dermaxx and it is very helpful

One aspect I didn't see mentioned yet is the ability for the animal to simply scratch her/himself for an itch.

A stiff, painful spine disables the dog/cat from doing so, as does hip pain, or missing and dysfunctional hind limbs. Imagine what it is like when it itches and you cannot scratch.

So regularly offering a good neck, ear, all over face scritch and scratch is one of the chores I included in keeping an animal friend comfortable.

Feli with her spinal issues needed scratching, and so does my cat Captain Jack who has incomplete hind legs, incl. missing paws.

Feels so good!