there's plenty of brush in my grandparents' pasture in the summer but do I have to feed in the winter? They have 13 acres and I'll only have 8-12 boer goats.
They do need a good loose goat mineral no matter what. If you get cold and snow, you will have to provide them with something. Plus if you are planning to have kids, then you will need to feed the moms so they produce good milk. And they will need some sort of shelter from the elements.