The big difference between a pig and a cowOne thing I'm very proud of is how much time my pigs spend out on pasture, eating grass, digging up roots, and generally being pigs. They're happier and healthier for it, and I believe the pork that comes from them is better in every way. But despite this, I never claim to sell grass fed pork, because my pigs are always eating grain along with pasture. So why can I feed cows and sheep nothing but grass and have them thrive, while pigs (and chickens) require grain? The answer is digestion.
Cows are ruminants, which means they have complicated stomachs that have an incredible capacity for breaking down cellulose, the tough fiber in which grass locks up protein and energy. Cows chew it multiple times, and they also have symbiotic bacteria in their stomachs which further break down the plant matter. Pigs, on the other hand, have a single stomach. Rather than being grass specialists, like cows, they are generalists. While they will eat plenty of grass and get some good nutrition from it, they are not efficient enough at digesting it to live on grass alone.
So no grass fed pork? What about acorns?No, as I just mentioned, all the pork I sell comes from pigs that have been fed grain as well as grass. While I'm comfortable saying no one raises pigs that are grass fed the way cows are grass fed, it's true that pigs' metabolic flexibility means they're capable of thriving on a varied diet. On my farm they love scarfing down apples in the fall, clover, roots of all sorts, and even expired bread or produce from the local health food store.
The most famous example of this is the Iberico pigs of Spain, from which comes the legendary Jamon Iberico. Even these pigs are started on a grain ration before being turned loose in oak groves, and even then only a very few are finished without any grain at all. Hams from these are labelled Jamon Iberico de Bellota, which, if you google it, you will see costs well over $100 per pound. So be careful when you see claims about "acorn fed" pigs. Any farmer with a few oak trees could claim to sell "acorn fed" pigs and not be telling an outright lie, but there's a world of difference between a pig that eats a handful of acorns and one that lives in an oak forest.
Theoretically, grass fed pork is possible, or at least not grain fed porkEven if it's not practical, it's possible to raise pigs without any grain supplements. There are millions of wild pigs in America, mostly in the south though at various times there have been small colonies in New York. (In fact, one of my neighbor's pigs got loose and roamed the land for the better part of a summer a few years back.) These are mostly the descendants of escaped wild hogs, though some of them have crossbred with escaped wild boar. They are certainly capable of surviving without direct grain supplements, though they are fond of corn fields, much to the chagrin of farmers.
And going further back, it used to be common to let pigs run at least somewhat loose in the woods, then to round them up once they'd fattened. Presumably these pigs ate little grain. But they ate lots of other stuff, from roots to the eggs of ground-nesting birds,, and they would take a huge amount of space to forage, while not doing anything particularly good for the environment. Managing pigs responsibly requires carefully channeling their potentially destructive behaviors like rooting and wallowing into the areas of a farm that need this very particular sort of disruption. Feeding grain allows them to grow well while ensuring the remain a net positive for the ecosystem of which they are a part.