NR: Had a similar situation with an excellent mare that I used on community pasture for years. Never had this happen before. She started doing stupid things and became untrustworthy around the kids.Totally out of character as I raised her from a baby.Turned her into a broodmare. Found out years later that the probable cause was either a lack of manganese or magnesium, can't remember which. One of them has to do with the nervous system. Also had a group of cows from B.C. that were known to be severely lacking in (manganese or magnesium). This was when I was at the University of Alberta research station.These little black cows were totally nuts.They'd start crawling the fence if you walked by the pen. Dr. Gary Matheson had us put them on a special feed (trying to build their bodies and blood levels back up. In about 2-3 months, their blood levels were back too normal and they started to act like normal cows again. Maybe a blood check on these horses wouldn't hurt if there are no other apparent reasons. Oh Yeah, this was before EXT'S time.