Very interesting. On a similar note, even though my mare's IR/PPID is well-controlled right now, she still cannot handle even the tiniest amt of fats--I tried adding the recommended ground flax (just 1oz/day, to start) and within 36 hrs she was PU/PD, hard crest, etc. which resolved quickly w cessation of the flax. Even when she was in hard work last year (eventing) I could not feed any kind of fat/oils w/o similar reactions. Alfalfa, however, she is quite fine with. Fascinating stuff. I hope one day we'll all get to the bottom of these crazy phenomenons for the sake of future horses...

Thank you for your response!
Kerry