my 13.2 pony has started to misbehave

Question
hi i have had my pony for about 7 months now and so far have got on with him quite well apart from the usual bad days that all of us sometime have. but just recently his behavior has become bad and hes started to rear up when im leading out of the field and sometimes go under the electric fence in his field and gallop all the way back to the yard also hes started biting and stomping and fidgeting about whenever i go to groom or touch his tummy and he does the same when having a rug put on. also when i ride him and i kick him on he tosses his head up and puts his ears flat back. at first i thought he might have been kicked under his tummy but when we asked an older person on the yard she said he was just being grumpy .another thing is he is in a mobile stable next to a grumpy mare that always goes for him , whether hes paranoid about this i don't know. please can you help me. thanks grace x

Answer
Grace I think it might pay for you to get a vet out to your horse, don't want to scare you but bad behavior like this can be from medical problems like a tumour or grass staggers. Your horse may also just be lacking in something so your vet may be able to advise you better than me as I can't actually see the horse. If he was just doing one or two things wrong then yes he is probably being naughty but to be doing all these things all of a sudden makes me think there may be more to it. good luck and let me know haw you get on. Karen