Bingo!
It's been a while since I spent time near a pig farm, but my recollection is that the general stench of a typical pig farm is well-nigh unbearable!
Shouldn't the issue be zoning, rather than what pig-feed you use?
I suppose, although I'm philosophically opposed to zoning laws as well. If someone built a hog farm next to your property and the stink lowered your property values, I think you could easily make a civil case however.
On the other hand, if the hog farm was there first, the type of feed being used wouldn't help you case in the slightest, at least with me.