I have a 19 year old TB mare who started to get arthritis last year. She is no longer able to canter, and can't trot that much. She is on Actiflex 4000, which is pretty good, but she still can't do much. I have heard some people use the Smartflex Senior and it has worked for them. Actiflex 4000 has more of every ingredient the Smartflex Senior has, but I would like to know about peoples experiences with both of them. Any info on effectiveness would be greatly appreciated!!!