My mare started this kind of behaviour around 6 months after I bought her.....she was horrible - ears back, trying to nip a lot (even when being brought up from the field), not nice to catch, and bargy and rude in the stable. I found out that she has arthritic changes to hocks and grade 3-4...
My mare has recently scoped clear of grade 3-4 squamous and glandular ulcers - still on 1/4 dose gastroguard to wean her off....I also feel hind gut issues may be involved too, so have started her on yea saac which is relatively cheap - I noticed a difference in her poos straight away. Also...