Boredom. My mare went to a new boarding home.. plenty of pasture available. Instead they kept her and her pasture buddy locked in a small corral because they wanted to be able to sit on their deck and look at the pretty green pasture once the snow was gone and spring grass came in??!! (My mare is a TB 16.2). She was accustomed to 20 acres. She was there 2 months, April and May. By beginning of May she was chewing on wood fencing, the barn.. gates, anything to relieve boredom. Her personality changed too. Got her out of there as soon as the snow stopped long enough to drive safely. On 6 acres… whole different horse.