Raising pigs on pasture alone

One of the things that I get questions on from customers is what I feed my pigs.  A mixture of complete feed, produce from super markets, bread and other human food that is past its prime or there's been some sort of accident that makes it available to me.  (Accidents like spearing the side of a container of pumpkin pie filling with a forklift.  The pie filling is just pureed pumpkin, but they can't use it in the food production because it's punctured - but the pigs like it just fine. 

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There's a segment of the customers who are puzzled by that - why don't I raise my pigs on grass alone, like the guy in vermont?   Or on acorns like the farmers in spain?   It's happened often enough that I have a standard talk - "well, that guy in vermont who claims to raise pigs on pasture alone, I offered him $10,000 to raise pigs per his claimed standards, and he declined.  "

There's no question that you could raise pigs on forage alone; wild pigs manage to do that every year, and in warmer areas of the country they've been so successful that they have become pests and are basically hunted without restriction.  If that's true, why not raise my pigs on forage alone? 

The claim made was that you could keep 20 pigs on an acre of ground and have those 20 pigs grow from weaned pig size to market weight on the forage they got from that amount of ground alone. 

So lets put some numbers on that:  to grow from 40lb feeder pig size to finished pig size at 250lbs is 210lbs of weight gain.   In a heated barn with very good nutrition and no immune challenges like the common cold - that amount of weight gain would take 520lbs of feed (2.5 lbs of feed per pound of gain).   

There's a lot of research on what to feed pigs and their nutritional needs vary by the growth stage they are in, but in a general sense we can get close enough for discussion by using the calorie value of a pound of corn (1660) and a pound of soybeans (2030).  Pig feed is about 70% corn and 30% soybeans, so (.7 * 1660 + .3 * 2030 = ) 1771 calories per pound of feed.

To raise one pig from 40lbs to 250lbs takes a little under a million calories in perfect conditions - remember, these pigs are in temperature controlled barns and are protected from disease or anything else that would impede their growth. 

That's different than the environment when they are raised outdoors.  My experience with pigs raised on pasture is that they consume more feed; in the early parts of the year they're using the calories to keep themselves warm, in the later parts to keep themselves cool, and all of the time to fight off all of the small ailments that they're exposed to in nature.  Every time they get a sniffle it doesn't hurt them, but it does hurt the efficiency of gain. 

So for this hypothetical pasture I'd need to grow roughly 20 million calories worth of food at a minimum, with the real number probably being closer to 30, in order to meet the nutritional needs of the pigs. 

Lets take a look at how many calories per acre various crops produce: 

Corn:  15 million
Potatoes:  15 million
Rice:  11 million
Soybeans:  6 million
Wheat:  4 million
Broccoli:  2.5 million
Spinach:  1.7 million

To get 15 million calories of corn from an acre you can't keep the pigs in the same area.  The corn has to be planted, grow and mature in order to get the full calorie advantage.  That is not what the claim
is:  the claim is you can keep 20 pigs an acre and have them get all of the food they need from that acre while they live here.   Even if you reduced the number of pigs by half - 10 pigs per acre - you'd still need to have the entire acre covered with either corn or potatoes that grew unmolested and were harvested when maximum calories were available. 

That's why I don't believe the claims of having raised pigs on forage alone.  Not in the area described, and not at the speed claimed ("10% to 20% slower than on regular feed"). 

Now it's entirely possible to raise enough crops to feed pigs on your own.  I'm doing that on my farm now - I plant separate acreage with corn and harvest that corn to form the bulk of my pig feed.  My pigs are kept outdoors, on vegetation - mostly alfalfa, which they enjoy eating - and they're given a ration of last-years corn to grow on.   In the winter the pigs allowed out,but choose to spend most of their time in the barn, sheltered from the weather. 

What would it take to grow a pig on pasture forage alone? 

To raise 10 pigs on pasture you need an acre of corn somewhere to feed them, or you need to provide enough acreage so that each hog has multiple acres to forage from, as wild pigs often do.  And you'll get a result that is closer to wild pig than farm pig - a much leaner body, a much smaller body, and much less fat.   I am not aware of any commercial pig venture that is doing that now.  Even iberico pigs in spain are fed a grain ration: 

BLACK label (100% Jamón Ibérico de Bellota) – 100% pure-bred Iberian black pig / Purely acorn diet during the Montanera (natural grain for the rest of the year) / 100% organic free-range / Aged for minimum 3 years

RED label (Jamón Ibérico de Bellota) – 50-75% Iberian black pig genes / Diet of cereals & acorns / 100% organic free-range / Aged for minimum 3 years

GREEN label (Jamón Ibérico de Cebo de Campo) – At least 50% Iberian black pig genes / Diet of cereals and natural pasture / 100% organic free-range

WHITE label (Jamón Ibérico de Cebo) – At least 50% Iberian black pig genes / Diet of cereals / Commercially reared