Carol you just reminded me - when my mare needed to be switched to different feed she threw a huge hissy fit (and she was always fussy).  We ended up doing a thin layer of the regular sweet feed on top of her grain to get her to eat it.  Fortunately she didn't have an issue with the ESC+starch in that feed in that amount but the list of things she stopped eating for no apparent reason stretched back much further than her diagnosis with PPID.