Pig feed is built on a foundation of cereal grains for energy and soybean meal for protein, with added vitamins, minerals, and sometimes enzymes or agricultural by-products to round out the nutrition. The exact recipe shifts depending on the pig’s age, size, and purpose, but a typical commercial pig diet in the United States is roughly two-thirds ground corn and one-quarter soybean meal, with the remaining fraction made up of mineral and vitamin supplements.
Grains: The Energy Base
Corn is the dominant energy source in pig feed across the U.S. and most major pork-producing countries. It’s high in starch, relatively cheap, and pigs digest it efficiently. There’s no upper limit on how much corn you can include in a swine diet, which is why it often makes up 65 to 85 percent of a finished feed by weight, depending on the growth stage.
Other grains can substitute for corn partially or completely without hurting growth. Wheat and grain sorghum (also called milo) are nutritionally close to corn and are common replacements, especially in regions where they’re cheaper. Barley works too, though it contains more fiber and about 5 to 10 percent less energy per pound than corn. Oats have the highest fiber content of any cereal grain used in pig feed, so they’re typically capped at around 30 to 40 percent of the diet for older pigs and used sparingly for young ones.
A major grain co-product in modern pig feed is distillers dried grains with solubles, or DDGS. This is the leftover material from ethanol production, usually from corn. It’s packed with protein, fiber, and fat, making it a useful and affordable addition. Growing and finishing pigs can eat diets with up to 30 percent DDGS without any drop in performance, and gestating sows can handle up to 50 percent. DDGS has become so widely used that it’s now a standard ingredient rather than a niche by-product.
Protein Sources
Soybean meal is the most common protein ingredient in pig feed worldwide. It supplies the amino acids pigs need to build muscle, and it pairs well with corn because each compensates for the other’s nutritional gaps. In a starter diet for young pigs (20 to 50 pounds), soybean meal might make up about 30 percent of the feed. By the time pigs reach finishing weight (120 to 230 pounds), that drops to roughly 12 to 15 percent because older pigs need less protein relative to energy.
Several other protein sources can replace some or all of the soybean meal. Field peas are a cheap source of amino acids with fewer anti-nutritional compounds than some alternatives. Fava beans are protein-rich at about 28 percent and also supply potassium, phosphorus, iron, and zinc. Lupin seeds range from 32 to 52 percent protein depending on variety. Rapeseed meal (canola meal) contains around 35 percent protein and is particularly high in sulfur-containing amino acids and phosphorus. In some operations, fish meal or other animal-derived protein is used in small amounts, especially for very young pigs.
Why Amino Acids Matter
Pigs don’t just need “protein” in general. They need specific amino acids, and the most critical one is lysine. It’s called the first limiting amino acid because it’s the one most likely to fall short in a grain-based diet. A growing pig (around 65 to 130 pounds) needs about 0.81 to 0.94 percent lysine in its diet. A finishing pig heading toward market weight needs only about 0.53 percent. Two other amino acids, threonine and methionine, are kept in a fixed ratio to lysine, typically around 61 to 63 percent and 28 to 29 percent of the lysine level respectively. When the natural ingredients don’t supply enough, synthetic amino acids are added directly to the feed to hit these targets precisely.
Vitamins and Minerals
Every commercial pig diet includes a vitamin and mineral premix, a concentrated powder blended into the feed at a few pounds per ton. The major minerals are calcium, phosphorus, and salt. Calcium carbonate and dicalcium phosphate are standard ingredients that supply the first two. Trace minerals like zinc, iron, copper, manganese, and selenium are also included in small amounts.
On the vitamin side, the premix typically provides vitamins A, D, E, K, several B vitamins (riboflavin, niacin, pantothenic acid, B12), choline, folic acid, and biotin. Because vitamin levels in natural feedstuffs like corn and soybean meal are unpredictable, nutritionists generally ignore whatever vitamins the grains contribute and formulate the premix to supply the pig’s entire requirement. The cost of doing this is low relative to the risk of a deficiency.
Enzymes and Other Additives
Phytase is one of the most widely used feed additives in modern pig production. Plants store a large share of their phosphorus in a molecule called phytate, which pigs can’t digest on their own. The phosphorus passes right through them and ends up in manure, creating both a nutritional waste and an environmental problem. Phytase breaks down phytate in the gut, releasing phosphorus, calcium, and other minerals so the pig can absorb them. This means farmers can add less supplemental phosphorus to the feed and produce less phosphorus-heavy waste.
Other common additives include organic acids to support gut health, probiotics (beneficial bacteria), and in some countries, low-dose antibiotics as growth promoters, though regulations on antibiotic use have tightened significantly in recent years.
How Feed Changes by Growth Stage
Piglets, growing pigs, and finishing pigs eat noticeably different diets. The youngest pigs need the most nutrient-dense feed, and the formula simplifies as they grow.
Prestarter diets for baby pigs just after weaning are the most complex. They often include dried milk products like whey and lactose to ease the transition from sow’s milk to solid feed. These ingredients are highly digestible and palatable, which helps piglets start eating sooner. Starter diets for pigs up to about 50 pounds contain around 20 percent protein and 1.1 percent lysine, with soybean meal making up a large portion alongside corn.
By the finisher stage, when pigs weigh 120 to 230 pounds, the diet shifts heavily toward corn. A typical finisher feed is about 85 percent ground corn and only 12 to 13 percent soybean meal, bringing the protein level down to around 13 to 14 percent and lysine to 0.6 percent. Vitamin and mineral premixes are also reduced. The goal at this stage is cheap energy for the final push to market weight, not rapid muscle building.
Feed Efficiency in Practice
All of these ingredients come together to produce one of the more efficient livestock systems. The U.S. industry average feed conversion ratio for finishing pigs in 2023 was 2.82, meaning it took 2.82 pounds of feed to produce one pound of weight gain. Measured from weaning all the way to market, the average was 2.61 pounds of feed per pound of gain. The top 10 percent of operations achieved a wean-to-finish conversion of 2.43, showing how much diet formulation and management can move the needle.
What’s Prohibited
Federal regulations restrict certain materials from pig feed. The most notable rule bans specific cattle-derived materials to prevent the spread of mad cow disease (bovine spongiform encephalopathy). Brains and spinal cords from cattle over 30 months old, carcasses of cattle that tested positive for BSE, and certain processed beef products derived from these tissues are all prohibited from any animal feed. The FDA also bans specific chemical substances, like the dye gentian violet, from animal feed when they haven’t been proven safe. Beyond federal rules, many feed mills follow additional quality and safety protocols set by industry organizations.