I've given a bunch of different supplements over the years. Currently I am giving the girls (8 & 10) Springtime's Joint Health and Fresh Factors, as a support/preventative. Neither one has any arthritis or other health issues, but both raced before they became broodies, so I figure it can't hurt Fletcher (10) has pretty bad arthritis, and started having problems starting about 6 yrs old. Currently he is on Arthrisoothe Gold and Fresh Factors. I switched to the Arthrisoothe Gold because it has Green Lipped mussels, Boswellia, and Yucca as well as the usual stuff. I get it from Amazon. I have arthritis myself, and know that boswellia, at least, does help.
btw, Fletcher is a racing school drop out, never raced
edited to add, Arthrisoothe Gold: (per tablet, he takes 2/day)
glucosamine 500 mg
msm 500 mg
chondroitin 200 mg
green lipped mussel 200 mg
boswellia serrata 90 mg
yucca schidigera 90 mg
vitamin C 60 mg
type II collagen 32 mg
zinc 7 mg
hyaluronic acid 6 mg
vitamin E 60 IU