Breyer horses are considerably more lucky than real horses in the case of broken legs. (Although this is a debatable point. For one thing, a real horse's leg is unlikely to break OFF. For another thing, real horses aren't as prone to broken legs from falling off shelves or being dropped.) While we all know what cowboys do to horses with broken legs, a Breyer horse's broken leg can simply be glued back on.
The first task, of course, is to find the other piece of the leg. This can be tricky, since the broken bits can be vacuumed up unnoticed, or skitter under the couch. Read more