I have a 5 year old OTTB. Back in June she tyed up. I was wondering, did they test your horse’s vitamin E and selenium levels? A deficiency can cause issues and my mare was slightly deficient in both. To be safe I placed her on a low starch food and did a lot of research around it. Pyro a Ultium is an excellent high fat low starch food. My mare was on it but it got to be quite pricey. I did further research and found that Blue Seal sentinel LS had almost everything the same as the purina and was approximately $7 less a bag. My horse seems to be doing well! On top of a feed change I dad vitamins E, selenium, and magnesium to her diet through a supplement that is meant for horses that tie up. So far so good! Best of luck!