To shed some more light on this topic since I am the owner of this mare.........the vets can find nothing wrong with her! We have done everything under the sun to figure this out. Yogurt, Probiotics, everything, to make a long story short. We tried pulling her off grain and she is fine, we tried putting her a on special low carb grain, worked great for about 6 weeks, then the diarhea came back again. Had someone suggest it was not the carbs she was not tolerating but the starch/corn so we put her Vintage Performance LS, low starch, Again, worked for about 6 weeks and the diarhea is back. We have tried everything for over a year and a half! NOTHING works. And to top it off, her filly we have here hit 6 months old and guess what? SAME THING! She is now on the low starch grain and doing fine. But now the vet is even more stumped as it seems to be a metabolic disorder that now seems to be hereditary! So, I give up! We have yet again pulled her completely off grain and have put her up for sale!