why a horse would suddenly turn on its field mates (V. aggressive)- horse has been moved yards recently and has never been violent towards other horses before - no other apparent changes to management???
Only other thing I can think of is if horse is feeling unwell (they can genuinely get over-sensitive & defensive - presumably a survival thing so as not to show a weakness) OR horse is being over-fed & under-worked - we have a problem on our yard at the moment with a horse being fed competition mix to be ridden 2/3 times a week, poor bloody horse is acting like a hyper-active child & other horses are suffering for it (problem will soon be solved I think).