In 2024, the National Pork Board (NPB) initiated an unprecedented effort to better understand the efficiency of nutrient utilization in swine. Understanding how nutrients flow, from feed, through the pig’s body to manure to crops and back again, provides accurate Life Cycle Assessments (LCAs) and carbon footprint calculations – as well as insights into how these footprints can be reduced through changes to farming practices. And while feed is where there’s the most opportunity for pig farmers to reduce their footprint (it represents 70-80 percent of the production footprint for monogastric animals like pigs and chickens), manure practices also makes a difference.
NPB wants to encourage their members to complete a voluntary LCA, and to make that easy, NPB created the ‘Nutrient Flow Consortium’ of experts from five institutions, across soil science, agronomy, economics, animal science, systems modeling and agricultural engineering. The Consortium is partnered with Institute for Feed Education & Research (iFEEDER), established in 2009 by the American Feed Industry Association and its associates to support research and education towards a more sustainable feed and pet food supply chain.
LCA framework
Completion of an LCA involves a lot of data, including calculations of the carbon involved in the transport of feed ingredients, whether they are grown on farm (using pig manure or not using pig or other manure, and how), how crops are grown, where crops are processed and so on. Data from research into the flow of specific nutrients is needed in an LCA, flowing from grain and other raw feed ingredients to the growth of pigs to their manure and what happens to these nutrients in the field (e.g. emissions) when that manure is applied. This research is ongoing.
In addition, feed and additive manufacturers continue to help farmers reduce their farm footprints (through higher feed efficiency) through innovations in processing and product development, and farmers can also tweak their feeding strategies. For example, farmers who grow corn for their own pigs will have a lower LCA than if they sell it for ethanol production and the distillers grains co-product is then transported back to their farm for pig feed.
In the area of manure management, pig farmers can shrink their footprints by changing manure storage, processing or field application strategies. “What you can economically pick and what makes the most difference vary by region and the manure systems you are currently using,” explains Daniel Andersen, a Consortium member and associate professor of Manure Management and Water Quality at Iowa State University. Farmers must obviously also follow their state’s regulations on manure application, and soil nutrient level restrictions. There are also state differences in on-farm funding schemes, differences among farmers in their capacity to invest in their farms, and so on.
Overall, Andersen stresses that “with manure systems, it really comes down to what we can do to limit methane and ammonia emissions from collection and storage, and how we can improve nutrient recovery and use in the field. Thinking of it as a system that needs to minimize losses and maximize the fertilizer value of the manure will continue to drive us forward.”
Footprint impact
Obviously, farmers want to spread their pig manure on their own farms or nearby fields. But both Andersen and Mahmoud Sharara, Consortium member and director of the Animal & Poultry Waste Management Center at North Carolina State University, stress farmers need to capitalize on all nutrients in the manure. “The opportunities to lower the farm LCA through manure management vary with farm context but always point to full valuation of manure components, macro and micronutrients (N, P, K, Mg, Ca, S, B, etc.) as well as carbon,” says Sharara. Andersen notes, “while we’ve often made decisions based on N needs, we have to keep N, P and K in balance to maximize the value of the manure, and thereby achieve the greatest replacement value for the emissions saved by not producing commercial fertilizers.”
In areas with insufficient acreage for manure application, Sharara and Andersen note the priority becomes implementing technologies to conserve and transform nutrients into transportable form. Sharara points to solid-liquid separation for transportation of the nutrient-rich stream as a recommended strategy. He also reminds farmers that reducing emissions during storage and treatment should be a priority, so consider installing covers for lagoons and slurry storages to limit ammonia loss, or adding acids to reduce methane/ammonia emissions. Digestion as a key practice to reduce methane emissions, which could take the form of heated, mixed anaerobic digestion tanks. “The choice for any particular operation will depend on farm size, project costs and potential economic returns,” says Andersen, “from the generated methane or electricity.”
Controlled aeration of manure storages is another opportunity to reduce methane and odorous emissions without increasing ammonia losses. In this area, Andersen calls for more research into the potential of low-rate aeration to reduce electricity costs during treatment, and to help find the best places for implementation. On that note, Andersen says that for operations using in-barn manure treatment and where constructing a digester and a new manure storage may not be cost-effective, aeration and acidification may be the best methane mitigation options.
More frequent emptying of storages also holds potential to minimize emission of methane. “But we need to make sure we aren’t just getting the manure out of the storage and getting rid of it. We have to be using the manure to support crop production and replace commercial fertilizer.”
Next steps
Andersen, Sharara and Erin Cortus University of Minnesota have, in a new paper, identified gaps in knowledge in mass and energy balances in four manure processing technologies (anaerobic digestion, aeration, solid-liquid separation and acidification), with these balances serving as the basis for LCAs and the holistic evaluation of various manure management scenarios. “Through this effort, we synthesized the literature into estimates of the fate and form of manure nutrients resulting from each technology,” says Andersen. “We also provide recommendations for adopting these technologies across different swine manure storage systems as well as opportunities to stack technologies to realize additional benefits.”
This work will help farmers and crop consultants understand how changes in one part of a farm system ripple through the rest of the operation, Andersen explains. An impermeable manure storage cover will influence the manure’s fertilizer value, or changes in pig diet might alter the number of acres that can be sustainably supplied with nutrients. “To support these decisions, we’re developing data and tools that allow farmers to evaluate ‘what-if’ scenarios and see how management changes affect whole-farm outcomes,” says Andersen. “These tools are designed to make trade-offs more visible, capturing impacts on nutrient use efficiency, emissions and overall system performance.”
Looking forward, the team aims to help farmers and advisors better understand and apply these tools in real-world decision-making. “Second, we are working to integrate this science into existing greenhouse gas accounting and LCA frameworks,” says Andersen, “so farmers can receive appropriate credit for the manure management decisions they make, whether that’s reducing methane and ammonia emissions through treatment technologies or more fully capturing the fertilizer value of manure nutrients.”
EXTRACTION OF NUTRIENTS FROM SWINE MANURE: NEW RESEARCH
Consortium members Dr. Priscila Cruz, Sailesh Menon and Dr. Charles Rice at Kansas State University just published a new brand new review of how manure management and cropping practices can reduce swine farm environmental impact. In the area of making nutrients transportable and easier to use within today’s more-precise fertilizer programs, they mention “advanced manure treatment technologies” such as struvite precipitation (SP). Struvite is a stable mineral composed of magnesium ammonium phosphate.
A few years ago, a group in Korea used SP to remove N, P, copper and zinc from swine manure (digester effluent). At an optimum pH, mixing intensity and mixing duration, they achieved removal rates of NH4-N and PO4-P of 74% and 83%, and for copper and zinc, 74% and 79%.
In 2025, a team in Thailand recovered over 85% of P in swine wastewater using SP, and a cumulative phosphate release from struvite of 51% by day 30. In their economic assessment for four struvite production scenarios, they pegged the cost of struvite production at $6.56 USD/kg of P.
Also in 2025, a team in Vietnam used a novel fluidized-bed homogeneous crystallization (FBHC) process with SP for single-step co-recovery of PO43− and NH4+ from swine manure. Under optimal conditions (pH 9, reaction time of 24 minutes, etc.) removal efficiencies reached 97% and 87% respectively, with recovered struvite achieving 94% purity. This prompted the team to conclude that their strategy is effective “for simultaneous nutrient removal and production of a value-added fertilizer.” Companies in Spain are also evaluating FBHC-SP through Spain’s Cartif Research Center, with funding from the European Union’s Nutriman Network.
