Elf On A Shelf
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In most racing yards horses are only dealt with in their stables to either be tacked up or groomed down. A lot of yards tie them up for everything they do - muck out, tack up, groom etc. So he may not be used to you doing things loose. They would also anticipate being ridden when people are around if they haven't already been out thay day. His stable is also his place. His sanctuary away from the world. Give him time to adapt. You've not had him long. Treat him for ulcers, it certainly wouldn't hurt.