The role of feed in sustainable pork production: 2023

August 2023

Lee Johnston1, Zhaohui Yang2, Pedro Urriola3, and Gerald Shurson3

1West Central Research and Outreach Center, Morris, 2Nutribins, and 3Department of Animal Science, St. Paul

Nitrogen (protein) and phosphorus are the second and third most expensive components of swine diets, respectively, after energy. However, the cost of these essential nutrients is much greater because only 10 to 44% of nitrogen and 34% of phosphorus in swine diets is converted into boneless edible lean pork. Similar inefficiencies also apply toward producing meat, milk, and eggs from other food producing animals, and are the main reason why the global livestock and poultry industry contributes about one-third of total human-induced nitrogen emissions. As a result, implementing practices that improve nitrogen and phosphorus utilization and reduce the carbon footprint of animal production systems are necessary to improve the sustainability of pork production.

About 68% of nitrogen emissions and 47% of greenhouse gas (GHG) emissions, which include carbon dioxide, methane, and nitrous oxide from livestock farms, are associated with feed production. Traditional approaches to swine diet formulation have focused on minimizing cost while meeting energy and nutrient requirements to achieve acceptable growth performance and carcass characteristics.  But, often little regard for minimizing environmental impacts of pig feeding has been considered in diet formulations. 

Types and sources of feed ingredients, approaches to diet formulation, and feeding practices affect the pig’s efficiency in gaining lean tissue (meat) and the environmental impacts of pork production. Precision diet formulation and feeding programs can reduce cost of production by more than 8%, diminish protein and phosphorus intake by 25% and excretion of these nutrients by 40%, and drive down GHG emissions by 6% through improved efficiency of nutrient use on commercial pig farms.  In an effort to learn how Midwestern pig farmers could improve the environmental sustainability of pig feeding, we conducted a series of studies (funded by the United Soybean Board) to determine the nitrogen and phosphorus use efficiency of different pig diets formulated to precisely meet the pig’s dietary nutrient requirements.  The standard diet was made with ground corn and soybean meal which is typically how pigs are fed in the Midwest.  We formulated three different experimental diets that contained reduced protein content, or distillers dried grains with solubles (DDGS, a by-product left over from making ethanol from corn), or reduced protein and DDGS with specific nutrients included.  All diets included an enzyme additive to help pigs completely digest nutrients present in the feed. 

From the results of these experiments, we learned that pigs grew similarly regardless of the diet they consumed.  This result told us that we satisfied the pig’s nutrient requirements using four different approaches to formulating the diet.  This was good news!  Next we considered the pigs’ growth performance, the amount of pork produced by those pigs, and the environmental impacts of the four different diet formulations we tested using a Life Cycle Assessment (LCA).  Life cycle assessment is a systematic analysis used to measure the environmental impacts of inputs and outputs of products during their entire life cycle.  LCA approaches have been used to evaluate a range of products from cars to building materials to clothing to food, in our case, pork.  Our results showed that the standard feeding program based on corn and soybean meal was projected to have the lowest GHG emissions, and least impact in the areas of marine eutrophication, freshwater eutrophication, and fossil resource use.  The reduced protein feeding program had the least impact on acidification, terrestrial eutrophication, and water use among the four feeding programs evaluated.  The feeding programs that used DDGS demanded the lowest amount of land use. 

Our results demonstrated that the “best” feeding program for reducing environmental impacts can change depending on which measure of environmental impacts one uses.  None of the four feeding programs we evaluated were best in every category of environmental impacts.  Results from this study demonstrate how the use of LCA data for assessing various environmental impacts of feed ingredients, diets, and feeding programs can provide important information that enables pork producers to choose feeding programs that meet specific sustainability goals.

Moving forward, sustainable swine feeding programs must be based on using multi-objective feed formulation that establishes targets for high priority LCA environmental impact measures that involve nitrogen and phosphorus use efficiency, GHG emissions, water consumption, and land use in addition to meeting nutritional requirements to optimize pig performance and carcass composition at a reasonable cost.  The ultimate goal is to “get the right feed to the right pigs at the right time”. 

Adapted from the National Hog Farmer magazine July/Aug. 2022.