Its a goat thing!!!
Mine do it all the time. Perhaps it has something to do with shedding hair. If there is a fence they will rub along it putting a great deal if pressure against it. You have to have good strong fences for goats.
Maybe you should check for mites & lice, although lice dont tend to be a problem in summer.
I have seen a nifty scratching post for goats made from a sturdy upright pole with scrubbing brushes screwed onto it. Google ‘ goat scratching post’ & there are lots of photos.
Given a lovely rough surface to rub against it may stop them from using your fence. I have this image in my head of them queing up in an orderly fashion for their turn at it[size=78%] ......[/size]