Greetings and welcome to BYH. That doesn't sound "normal" to me... I always understood that pigs are actually quite "clean" animals and tend to relieve themselves in one spot far from where they normally hang out. Is it possible that you've placed their shelter on top of an area that was previously used by pigs as their bathroom area? Anyway, I'll tag a few folks who might be able to help: @misfitmorgan @NH homesteader @Mini Horses @purplequeenvt and there are quite a number of others as well. Hope you'll stick around and share some pics of your animals with us. We're a bunch of shameless pic addicts. There's quite a bit of info an d knowledge in the pig section. Browse around and make yourself at home!
Just haven't had much need or anything of value to add to existing posts. Still try to earn my greeter's badge and say hi/welcome the newcomers 
They wouldn't even root it up, save one very neat corner scoop out where they slept, even tho they rototilled all around it outside!