I checked on Faith every couple of hours last night, and her attitude and behavior did not seem to change. Her temp remained consistent and her sweating ended. She finished the rest of her grain around 2am, but still has not touched any of her hay. I pulled it out of her stall and gave her some "fresh" stuff to entice her, but she's not interested. I'll keep monitoring her throughout the day.
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TBDancer made a comment last night that this may be to her being in season - thanks for bringing that up! We had a new horse arrive thjs past weekend and he was successful at licking her face over the fence and getting her to come into heat. (Apparently it doesn't take much these days...) This could definitely be why her attitude has changed, but I've never had a mare that has altered their eating habits so drastically due to a hormonal change. Have any of you experienced this? I'm keeping my fingers crossed that this is the cause of her recent behavior and discomfort.
Thanks for everyone's advice and well wishes! It means a lot!