Rats do get arthritis(I have a dwarf blue hooded female who has arthritis in all of her joints), but they mainly get paralysis, and supplements won't help that. At least with paralysis, it's not painful, and they do ok with it. Just make sure their feet don't have problems and they can clean themselves. My little girl with arthritis gets glucosamine/chondroitin supplements as well as anti-inflammatories when she needs them.