I'm on year three with my pigs. I started out copying Sugar Mtn Farm's pig feeding program pretty closely - pasture/hay + whey as the source for the vast majority of the calories my pigs ingested (we even went so far as to buy our boar from Sugar Mtn!). I couldn't make that hog ration work though. The pigs grew slowly (taking 12 or so months to reach a market weight of 300 lbs), and a few of them didn't finish well enough to sell. Last year we fed the piglets a fully balanced corn/soy ration until they weighed about 100 lbs (approximately 14 weeks) and then changed them over to the hay and whey diet for the most part. This winter some of them "fell apart" though and we are now of the opinion we need to take them to an even bigger size on a fully balanced ration before changing them over to a low grain ration. As pigs get bigger their ability to digest roughage improves. Mature boars and sows of the right lineage can do fine on pasture alone. The smaller digestive tract and greater relative-to-body-weight nutritional needs of little pigs makes them perform poorly on a diet with inadequate energy in it. I am sure it would be possible to breed pigs that could survive, nay thrive, on pastures with minimal supplementation. I don't think many farmer's can make money selling them for meat though. The time it takes to grow out a mostly grass-fed pig is too great (or the price of pork is too low).
The new plan is to take the pigs up north of 200 pounds on a non-GMO corn/soy blend with ad lib hay and whey. Then we'll wean away the high octane fuel and let them finish on hay, whey, and a limited ration of barley or other non-GMO grain. With adequate time on a very forage rich diet the flavor and quality of the pork will continue to be superior. Bland modern pork is the largely a product of the bland corn/soy that goes into hog feed. By continuing to feed "alternative" rations during finishing our pork will still retain its exceptional quality. The quick push through the lower weights with high density feed will allow me to finish whole groups of pigs simultaneously so that I can gain a little bit of efficiency on the trucking to/from the butcher. The small pigs will also be happier since their voracious appetites will be better sated by a "regular ration" while they're growing at peak rates.
The sows will stay on the hay/whey diet during gestation. While they're lactating I feed them so a grain ration so they have the energy they need to make milk for their young. Sows are pretty incredible in their ability to ramp up their metabolisms for a sharp spike in milk production. I've read that at peak lactation a 400 pound sow can make as much (or more!) milk as a 1200 pound cow. The sow only keeps that up for about 2 weeks though. Cows keep going for months. The sows in this video are about ready to pop - in farmer parlance "they're bagging", meaning their teats are swelling up in preparation for the milk they're soon to produce. The big black pig center-right is a boar, not a sow. Look closely as his mouth and you can see his tusks beginning to push his lips into a permanent snarl.
Since I wrote this blog post the sows have all farrowed. We're swimming in piglets (pictures and post next week). If you want to raise your own, we'll have weaned pigs ready to go the first week of June.