By Alice Rocha 

Of all the livestock animals raised in agriculture, swine are the ones that are the most similar to humans, genetically and in what they eat and how they digest food. They differ significantly from other animals found on farms such as ruminants like cattle, goats, and sheep.

Unlike ruminants, swine are categorized as monogastrics. This means they have “simple stomachs,” much like humans do. They are omnivores, capable of consuming animal and plant matter as part of their diets.

Ruminants, on the other hand, have a more complicated digestive tract. While they still only have one stomach, it contains four unique chambers each with a specialized function. The first chamber is called the reticulum, which is characterized by a honey-comb pattern in the tissue. This chamber is involved in particle sorting. Particle sorting is part of rumination, which gives ruminants their name. Rumination involves regurgitation, re-mastication, and reingestion of feedstuffs. And this process only happens when feed particles are too large to be properly digested by the microbes. The next chamber, the rumen, is the largest and is the primary site of digestion and where the majority microbes responsible for feed breakdown reside. Feed then travels to the omasum, which has book page like layers of tissue that help with water reabsorption. The final chamber is called the abomasum. This chamber is the glandular stomach of a ruminant and much like monogastric stomaches, releases secretions to continue digestion before feed reaches the small intestine.

Hogs’ simple stomachs are acidic and are the primary site of digestion, allowing for nutrients to be broken down before heading to the small intestine for absorption (or further digestion in the case of things like fat). However, this means that they are not designed to digest fibrous plant matter because they lack the same symbiotic relationship with bacteria and other microbes as ruminants have in their digestive tracts. Therefore, we must feed swine (and other simple-stomached animals) differently.

What do Pigs Eat?

A common swine diet can be composed of a wide variety of ingredients. The types of feeds found in swine diets can vary depending on the location of the pig farm. Soybean meal, barley, corn, oats, and wheat are all commonly used feed ration ingredients. There is a common misconception surrounding swine that these animals only eat waste. These animals consume whole grains and byproducts, which are commonly used in many livestock diets. Byproducts are not waste, but rather coproducts coming from the production of materials for human consumption, like cotton for clothing, soybeans for oil, and wheat for flour. The byproducts coming from these primary crops, for example the wheat grain, are otherwise still edible and useable. Feed availability is not the only thing that varies across swine diets. Just like a child has different nutritional needs compared to a mature adult, growing pigs have different requirements compared to pregnant or lactating sows. Each diet is designed to meet the specific needs of those animals. A young piglet will need protein to support growth, whereas a lactating sow will need sufficient energy to support milk production for her litter.

Swine diets are high in caloric energy, coming predominantly from carbohydrates and fat, compared to ruminant diets, which are higher in fiber. Grains such as corn are a good source of energy and make up most swine diets. Another important consideration in swine diets is protein. Like in people, protein is essential to growth and reproduction and is vital to raising healthy pigs. Soybean meal, this is a byproduct from soybean oil production, is an excellent source of protein and is a common feedstuff for swine. Amino acids, the building blocks of protein, also need to be balanced in swine diets. All animals have requirements for specific essential amino acids, which are needed to support normal growth and development but cannot be synthesized by the animal itself or are synthesized in insufficient quantity. The amino acid composition of proteins being fed to swine also requires thorough assessment to ensure the health of the animals.

What is the Environmental Footprint of Swine?

Like with cattle, we are able to measure the environmental impact of swine production by tracking the resources needed to produce a specific quantity of pork. The carbon footprint of swine production was estimated to be about 2.5 kg carbon dioxide equivalents (CO2e) per pound of dressed carcass in 2012. Another life cycle assessment from 2015 estimated the carbon footprint to be 2.85 kg CO2e per four ounces of boneless pork. While it looks negative that the carbon footprint is increasing overtime, the differences in functional unit between the studies leads to such differences (i.e., dressed carcass = post-harvest, prior to processing; boneless pork = post-harvesting, post-processing). However, both studies and others concluded that feed production is the main contributor to the environmental impact of swine production, due to the reliance on land, artificial fertilizers, fossil fuels, and water associated with cultivating grains.

Given the high environmental impact of feed production for swine, this becomes an area of interest that has potential to help reduce negative impacts. As byproduct feeds are equally nutritious compared to other feedstuffs, increasing their use in swine diets can help reduce the overall environmental impact of feed production.

Do People and Pigs Compete for Food?

In addition to environmental factors associated with feed production, there are social implications too. Corn is considered a human-edible grain, meaning it could be consumed by people, unlike other feedstuffs like soybean meal. The reliance on grains like corn can, lead to feed-food competition, which is defined as the tradeoffs associated with using human-edible crops and other resources to feed people directly or to feed livestock. This calls to question how to best use resources that are valuable to both the human food chain and the livestock production chain. Even so, swine are also capable of consuming byproducts (I.e., leftovers from crop harvest, processing, etc.) like ruminants do. The inclusion of byproducts into swine diets is limited by the nutritious quality of the feeds. Ingredients like alfalfa meal can only be used in limited quantities due to high levels of fiber.

Despite the tensions caused by feed-food competition, there is still plenty of opportunity to develop alternative feed sources for pigs. A feed company in The Netherlands called Nijsen/Granico has created swine and poultry feed from human food surplus from factories and bakeries. They source breads, other baked goods, and chocolate from 70 different facilities across the country, transforming food that would otherwise end up in a landfill into dry feed. While such a facility does not exist within the United States yet, it offers a potential source of inspiration for local feed companies to explore the potential that food surplus and food waste holds when it comes to feeding livestock like swine. About 40% of all food is wasted in the US and if we are able to put this waste to use, we are making swine production more sustainable.

The CLEAR Center receives support from the Pork Checkoff, through the National Pork Board.