Thanks everyone! To answer some of the questions coming up...
Sandie is turned out every day from about 7am after her breakfast until 3pm to come in for her dinner. The pastures have SOME grass but are by no means lush...but the BO throws a TON of hay out in the pastures each day for the horses to eat so they are NEVER standing around not grazing.
When they come in, they each have a mountain of hay in their stalls to eat right away along with their grain, so I'm not sure it's that she isn't getting enough to eat....although perhaps the fiber intake is just not high enough? Is there such thing as a fiber supplement for horses??
She has a mineral block in her stall and definitely eats it. She also has toys -- empty milk jugs hanging on strings with treats in them, a Lik-It, and a jolly ball too. So I don't think she's bored...esp since she's out all day, then I come ride her after her dinner, so she's only really in her stall at night to sleep.
I put hot sauce all over where she has been chewing today to hopefully stop her from doing any more harm to the barn and to herself, but I need to get to the bottom of what is the root of the problem and take steps to fix it before I have a cribber on my hands too!!!
"The times when you have seen only one set of footprints in the sand, is when I carried you..."