My Rottweiler was diagnosed with Hip Dysplasia and tendenitis, so of course she has horrible secondary arthritis. I have been successfully helping her with the following supplements. I found a wonderful liquid Glucosamine supplement at a tack shop it contains Glucosamine Sulfate, Glucosamine HCL,Chondroitin Sulfate, MSM, Manganese Ascorbate, Vitamins A,C, and natural mixed tophererols -Vitamin E. The liquid is easy to add to her food, and it gives you the amount to give for the weight of the pet. I also make sure she gets plenty of Omega 3, 6 and 9 fatty acids, the best oil I found is Hemp seed oil which can be found in most health food stores. I also give her canned sardines packed in water, Canned wild Alaskan Salmon, ground flax seeds, flax seed oil, I have also given her Fish body oil, never fish liver oil or cod liver oil (if you are feeding kibble it is not advisable to give fish liver oils). I give her yucca root (I order from Solid Gold dog foods), I give Yucca to her 4 days on 3 days off this is for the inflammation from the arthritis. I will take her off Yucca for about 3 months each year and supplement with either ginger, turmeric, Bromelain or Boswellin.
I also make sure I feed her a few raw meals each week, usually for supper. I add digestive enzymes to her raw meals and live active bacterial cultures or organic plain yogurt with active bacteria cultures. I add a raw egg shell and all and put it in the blender with different veggies, garlic cloves, etc.
I never feed her any veggies from the nightshade group which would be veggies like white potato's, tomatoes etc they increase inflammation.
I also made sure she is on a good dog kibble, I give her a few turkey necks and raw bones with cartilage on them to give her back the cartilage she requires.
For exercise, I make sure it is consistent. There are no long hikes on one day then a short one the next day. All her walks are the same, if I want to increase the hikes for summer I do it gradually. Swimming is wonderful exercise for a dog with arthritis as there is no impact on the joints.
Good luck to you, my Rottweiler is now 7 and she is in great shape. Even the vets are amazed at how well she is doing. You would never know by looking at her that she is in such rough shape
Here are a couple of websites to check out as well
http://www.solidgoldhealth.com/products/showcat.php?cat=3
http://www.activexamerica.com/syn-flex/index.php