How old is your horse?
I changed my horse's name for protection reasons. He's in the horsey witness protection program now so his previous abusers don't come looking for him
I have a tendency to give my horses a million nicknames anyway, so I never bothered changing their "real" name. The horse we have now, though, we have no idea what her name is/was so when we got her my daughter renamed her. We haven't had any major injuries, but she is the most clumsy/accident prone horse I have ever had and constantly finds new ways to give herself minor boo-boos -- I don't think that has anything to do with the name change, though.