My horse did the same thing with his flax that your horse did.  He suddenly refused anything with flax it in it.  He started eating it again when I bought bulk flax seeds from the feed store that I grind fresh myself.  I can only think that the "fresh" ground packaged flax (it was human grade) that I had previously fed must have been off.  They are far more sensitive to smell and taste than we are.  Now my horse happily eats his bucket of supplements with a cup of ground flax 2x per day. 

It's worth a shot to try and it is much, much cheaper.  Good luck, I hope it works!  (fingers crossed on the blood work for your mare - and curb chain jingles for luck!)


--
Joy and Willie (PPID/IR)
Nevada County, CA - 2019

Case history:  https://ecir.groups.io/g/CaseHistory/files/Joy%20and%20Willie
Willie's photo album:  https://ecir.groups.io/g/CaseHistory/album?id=242526