You just reminded me of the Islamic anti-pig propaganda that they eat their own faeces and are filthy. Pigs are actually the only farm animals that separate their sleeping area (which they keep spotless) from their latrine areas. And they definitely don't eat their own faeces.
It's a well-known fact that pigs DO practice coprophagia - the eating of feces. They will eat it if there is enough plant contained in the feces to interest them. Just google "coprophagia+pigs" and you'll get reputable farm and animal sites that confirm this. It's not propaganda in the least. But it is true that chickens do it too.
Farm swine (as opposed to pigs that are pets)
are disgusting. When we visited my great-grandmom's farm in the deep country as a kid, I couldn't even get near the pig pen because it smelled so awful. All animals smell a little, but the pigs - woosh! - couldn't get within 10 feet of their living space. I spent my later summers working and riding at a stable with 50 horses in one place, and it didn't smell anything NEAR what 9 or 10 farm pigs smell like. I gag thinking about it.
Chickens also eat their own faeces.
This is true. But they are not half as offensive as pigs - who will eat most things given to them. There is a reason why many old farmers say "slop the hogs" instead of "feed the hogs".