yes, i have lots of experience! I had a mare with PSSM and she was really well on Triple crown lite. But not only the grain is important, a hay low in NSC , also the additional supplements and an alternative energy source. I gave my mare flax seed 0,5 cups 2x a day and also Magnesium and Vit. E, VERY important. Also as an energy source ALCAR ( acetlyl l- carnitine) you can buy on ebay for example, 1 gr per 100 pounds body weight. ( 1200 pounds - 12 gr.) That made a HUGE impact on my mare. Also know that exercise is the key!
Definitely look into senior feeds. Not sure what's available in your area. Triple Crown Senior is pretty low.