I find keeping the pigs on pasture leaves almost no smell, and we get a bumper crop of wheat or corn silage when we move them. It is always a good policy to source as much feed as possible on site or from free sources such as restraunt or school canteen waste food (local health laws permitting!)
I also run some pigs in the woods from September to November to clean up the acorns, crab apples, beech nuts etc, then sell them on the Christmas market at a premium as organic acorn fed pork (mostly oak smoked)>