Hi, Irish : )
Sorry to hear your mare is uncomfortable. My knee-jerk reaction would be to check stifles and specifically hocks next. A flexion test might help pinpoint the area of concern, enough to allow for a progressive chat with your vet. After chatting with a vet for more definitive diagnostics, MSM, tho can take anywhere from 2 weeks to 6 months to show effect, can be an inexpensive yet effective way to go to start. Be advised, however, that any products might have their short-comings as well as their positives. All depends on the horse, of course ; )
My mare would buck going into canter due to arthritic hocks. The diagnostics were pricey but the specific diagnosis gave us a cheap, long-term fix since I knew EXACTLY what I was dealing with, to what degree and where. This made the trial and errour of supplements far less expensive and the repair more timely. Knew specifically what I wanted for product instead of running thru the expansive gamut of just inflammation supplements to find the ONE that works best.. Hope this helps you/makes sense, been battling a truly nasty cold for three days, not thinking all that clearly yet, sorry : )
Sure there's right and wrong but mostly there's just a whole lotta different.