Environmental impacts of eco-nutrition swine feeding programs in spatially explicit geographic regions of the United States

Gerald C Shurson; Rylie E O Pelton; Zhaohui Yang; Pedro E Urriola; Jennifer Schmitt

doi:10.1093/jas/skac356

. 2022 Oct 28;100(12):skac356. doi: 10.1093/jas/skac356

Environmental impacts of eco-nutrition swine feeding programs in spatially explicit geographic regions of the United States

Gerald C Shurson ^1,^✉, Rylie E O Pelton ², Zhaohui Yang ³, Pedro E Urriola ⁴, Jennifer Schmitt ⁵

PMCID: PMC9733525 PMID: 36305772

Abstract

This study was conducted to determine greenhouse gas (GHG) emissions, water consumption, land use, as well as nitrogen (N), phosphorus (P), and carbon (C) balance of five diet formulation strategies and feeding programs for growing-finishing pigs (25–130 kg body weight) in the three spatially explicit geographic regions where the majority of U.S. pork production occurs. Feeding programs evaluated consisted of 1) standard corn-soybean meal (CSBM) diets, 2) CSBM containing 15% corn distillers dried grains with solubles (DDGS), 3) CSBM with 8.6% thermally processed supermarket food waste (FW), 4) low crude protein CSBM diets supplemented with synthetic amino acids (SAA), and 5) CSBM with phytase enzyme (PHY) added at 600 FTU (phytase units)/kg of diet. An attributional Life Cycle Assessment approach using a highly specialized, spatially explicit Food System Supply-Chain Sustainability (FoodS³) model was used to quantify GHG emissions, water consumption, and land use of corn, soybean meal, and DDGS based on county level sourcing. The DDGS, FW, and SAA feeding programs had less estimated N and P intake and excretion than CSBM, and the PHY feeding program provided the greatest reduction in P excretion. The FW feeding program had the least overall GHG emissions (319.9 vs. 324.6 to 354.1 kg CO₂ equiv./market hog), land use (331.5 vs. 346.5 to 385.2 m²/market hog), and water consumption (7.64 vs. 7.70 to 8.30 m³/market hog) among the alternatives. The DDGS feeding program had the greatest GHG emissions (354.1 kg CO₂ equiv./market hog) among all programs but had less impacts on water consumption (7.70 m³) and land use (346.5 m²) per market hog than CSBM and PHY. The SAA feeding program provided a 6.5–7.4% reduction in land use impacts compared with CSBM and PHY, respectively. Regardless of feeding program, the Midwest had the least contributions to GHG emissions and land use attributed to feed and manure among regions. Water consumption per market hog associated with feeding programs was much greater in the Southwest (59.66–63.58 m³) than in the Midwest (4.45–4.88 m³) and Mid-Atlantic (1.85–2.14 m³) regions. Results show that diet composition and U.S. geographic region significantly affect GHG emissions, water consumption, and land use of pork production systems, and the potential use of thermally processed supermarket food waste at relatively low diet inclusion rates (<10%) can reduce environmental impacts compared with other common feeding strategies.

Keywords: amino acids, environmental footprint, feed formulation, food waste, life cycle assessment, swine diets

The addition of thermally processed supermarket food waste to swine diets has a greater impact on reducing greenhouse gas emissions, water consumption, and land use compared with corn-soybean meal diets without or with phytase, corn DDGS diets, and low protein corn-soybean meal diets supplemented with crystalline amino acids in feeding programs for growing-finishing pigs.

Introduction

Reducing the carbon (C) footprint and nitrogen (N) and phosphorus (P) waste in animal production systems is urgently needed to ensure global food security and sustainability. The earth’s planetary boundaries for N and P waste and recovery have been exceeded (Li et al., 2019; Sutton et al., 2019), which requires implementing practices that improve N (Uwizeye et al., 2020) and P (Oster et al., 2018) utilization efficiency, and reduce the C footprint of animal production systems (Gerber et al., 2014). Within agricultural systems, livestock production has been shown to be a major contributor to environmental pollution and land-use change because it requires significant amounts of feed, energy, and water; produces greenhouse gases (GHG) including carbon dioxide, methane, and nitrous oxide; and increases pollution risks from inefficient manure management practices (McAuliffe et al., 2016).

The environmental impacts of livestock and poultry production have been extensively evaluated in European countries but not in the United States where types and sources of feed ingredients, manure management practices, and production systems are substantially different. The U.S. Environmental Protection Agency (EPA, 2022) estimated that the agriculture sector contributes about 11% of the total GHG emissions, with livestock contributing about 3% of this total. However, these estimates are based on inventory values that only account for on-farm emissions from nitrous oxide and methane, and carbon dioxide associated with land use change. In contrast, European estimates are based on a Life Cycle Assessment (LCA) that accounts for embedded environmental impacts of supply chains upstream and downstream of livestock production. Life Cycle Assessment has become the international framework for determining the environmental impacts of agricultural production systems (Caffrey and Veal, 2013), and involves compiling and evaluating inputs, outputs, and environmental impacts of the system used to produce a product through its life cycle (van Middelaar et al., 2019). Therefore, by using an LCA approach, about 81% of global warming potential impacts in agriculture have been estimated to be associated with livestock production (Leip et al., 2015).

Globally, pork supply chains contribute about 9% to the total GHG emissions from livestock production, with swine feed production being the largest (worldwide) or second largest (United States) contributor (after manure) to these emissions (MacLeod et al., 2013; Pelletier et al., 2010). The major contributors to GHG emissions from swine feed production are nitrous oxide released from synthetic and organic fertilizers used in crop production (17% of the total feed emissions contribution); carbon dioxide released from energy used in field crop operations, crop transport and processing, and manufacturing fertilizer and synthetic feed materials (27%); and land-use change resulting from increased demand for feed crops (13%; MacLeod et al., 2013).

Because of the significant contributions of swine feed to the overall environmental impacts of pork supply chains, multi-objective feed formulation is an emerging approach being implemented in the global animal industry that uses LCA environmental impact data for feed ingredients to formulate least-cost, nutritionally adequate, low environmental impact diets (Mackenzie et al., 2016a; Garcia-Launay et al., 2018; de Quelen et al., 2021; Méda et al., 2021; Soleimani and Gilbert, 2021). The Global Feed LCA Institute (GFLI; https://tools.blonkconsultants.nl/tool/16/) has developed the largest database (962 feed ingredients) with the most LCA indicator variables (n = 18) using standardized guidelines and methodologies (LEAP, 2015). However, most LCA data in this database are not representative of ingredients used in U.S. swine diets and are based on country averages that do not account for regional or local differences (Notarnicola et al., 2016).

As a result, a limited number of studies have been conducted to evaluate LCA environmental impacts of feed ingredients and feeding programs in U.S. pork production systems. Most of these studies have focused on some of the environmental impacts of using corn distillers dried grains with solubles (DDGS) in swine diets but the results reported have been inconsistent (Lammers et al., 2010; Stone et al., 2012; Haque and Liu, 2019; Benavides et al., 2020). Furthermore, there are limited LCA data on the environmental impacts of feeding reduced crude protein (CP) diets supplemented with synthetic amino acids (Lammers et al., 2010; Benavides et al., 2020) or phytase enzymes (Lammers et al., 2010), which are common feed formulation practices used in U.S. swine feeding programs to improve dietary N and P utilization efficiency and reduce their excretion in manure. No LCA studies have been conducted to evaluate the potential for upcycling thermally processed pre- and post-consumer food waste sources into commercial swine diets in the United States which can significantly reduce the environmental footprint of the U.S. food system by preventing GHG emissions resulting from disposal in landfills (Shurson, 2020).

The environmental impact of corn and soybean production varies across states and regions in the U.S. (Smith et al., 2017; Pelton, 2018; Brauman et al., 2020; Pelton et al., 2021), and must be considered in LCA assessments of feed ingredients used in commercial swine feeding programs. The use of a highly specialized, spatially explicit Food System Supply-Chain Sustainability (FoodS³) model is an emerging LCA approach that can estimate commodity crop flows and quantify the environmental impacts of crop and livestock production at the county scale (Smith et al., 2017; Pelton, 2018; Brauman et al., 2020; Pelton et al., 2021). Spatial variation involving feed sourcing region and the associated life cycle environmental impacts have never before been considered in studies examining environmental implications of alternative animal feeding programs and diet formulations. Therefore, the objectives of this study were to conduct a streamlined LCA using the FoodS³ model to determine and compare the embedded (feed and manure) environmental impacts (GHG emissions, water consumption, land use; N, P, and C utilization efficiency) of feeding growing-finishing pigs fed corn-soybean meal-based diets without or with the addition of corn DDGS, synthetic amino acids, thermally-processed supermarket food waste, or phytase enzyme in three primary pig production regions in the U.S (Midwest, Mid-Atlantic, Southwest).

Material and Methods

Diet formulations and feeding programs

The system boundary used in this study was limited to examine only the impacts of diet composition of feeding programs and associated effects on manure production (excluding hog farm energy use, transport, feed milling, etc.) because these are the primary hotspots responsible for the majority of GHG emissions, land use, and water consumption impacts and are most directly affected by diet composition. Such an approach is consistent with other previously streamlined comparative LCA approaches (e.g., Hotspot Scenario Analyses; Pelton and Smith, 2015; Pelton et al., 2016).

Environmental impacts of five feeding programs for growing-finishing pigs were assessed using an attributional LCA approach which provided spatially explicit, regional estimates of feed commodity flows and environmental impacts of each alternative. Standard corn-soybean meal

(CSBM) diets containing 0.15% synthetic lysine and without feed additives or co-products served as the standard baseline feeding program. Four other iso-nutritious feeding programs consisted of CSBM containing 15% corn distillers dried grains with solubles (DDGS), 8.6% thermally processed food waste (FW), low CP and synthetic amino acids (SAA), or phytase enzyme (PHY; added at 600 phytase units [FTU]/kg diet to release 0.11% P). The DDGS feeding program was chosen because corn DDGS, which is a co-product of the United States ethanol industry, is the most abundant alternative ingredient that serves as a partial replacement for corn, soybean meal, and inorganic phosphate in commercial swine diets. According to the Renewable Fuels Association (RFA, 2022), 18% of the approximately 33 million tons of DDGS produced in 2021 was fed to swine in the United States In contrast, very little FW is currently used in commercial swine feeding programs, but it represents a significant opportunity to reduce diets cost and environmental impacts in pork production systems because of its widespread abundance and high nutritional value. Low CP diets containing adequate amounts of supplemental synthetic (crystalline) amino acids have become a popular feed formulation strategy to reduce diet cost and N excretion in manure while providing improved gastrointestinal health of pigs. Similarly, the addition of phytase enzymes and formulating swine diets on a digestible phosphorus basis has become a common and effective strategy for improving phosphorus utilization efficiency and reducing phosphorus excretion in swine manure.

A total of 20 diets were formulated to simulate the five 4-phase feeding programs for growing-finishing pigs from 25 to 130 kg body weight (BW). We chose to focus our analysis on the growing-finishing phase of production because it represents about 75% of the total feed consumed in a commercial farrow-finish operation. Nutrient requirements were determined using the swine NRC (2012) model for each of the four dietary phases (phase 1 = 25–50 kg BW; phase 2 = 50–75 kg BW; phase 3 = 75–100 kg BW; phase 4 = 100–130 kg BW). Diets within each phase were formulated to contain equivalent metabolizable energy (ME), standardized ileal digestible amino acids (SID AA), and standardized total tract digestible (STTD) of P using ingredient composition tables from NRC (2012) for all ingredients except FW. The ME, SID AA, and STTD of P for FW were obtained from Fung et al. (2019b). A linear least-cost diet formulation model (NSNG, 2010) was used to formulate each diet based on nutrient requirements and ingredient composition data from NRC (2012). A summary of the overall weighted average diet composition of feeding programs is shown in Table 1.

Table 1.

Weighted average of overall ingredient and nutritional composition (as-fed basis) of the growing-finishing pig diets used in each 4-phase feeding program

	Feeding program^a
Ingredient, g/kg	CSBM	DDGS	FW	SAA	PHY
Distiller dried grains with solubles (DDGS)	0.0	150.0	0.0	0.0	0.0
Food waste	0.0	0.0	85.9	0.0	0.0
Soybean meal (SBM)	192.0	64.9	110.4	126.8	191.6
Choice white grease	29.5	26.0	0.0	28.1	27.6
Calcium carbonate	9.8	11.0	10.3	9.9	12.5
Monocalcium phosphate	6.6	5.8	6.9	7.5	0.7
Sodium chloride	3.5	3.5	3.5	3.5	3.5
Vitamin-trace mineral premix	3.0	3.0	3.0	3.0	3.0
L-Lysine-HCl	1.5	4.8	3.5	3.5	1.5
L-Tryptophan	0.0	0.4	0.2	0.2	0.0
L-Threonine	0.1	1.2	0.7	1.0	0.1
DL-Methionine	0.0	0.3	0.5	0.4	0.0
Phytase	0.0	0.0	0.0	0.0	0.5
Total	1,000	1,000	1,000	1,000	1,000
Calculated values
Metabolizable energy, kcal/kg	3,440	3,440	3,440	3,440	3,440
Crude protein, %	15.53	13.80	14.18	13.23	15.55
Standardized ileal digestible amino acid, %
Lys	0.76	0.76	0.76	0.76	0.76
Thr	0.48	0.48	0.48	0.48	0.48
Met	0.23	0.25	0.25	0.24	0.23
Trp	0.15	0.13	0.13	0.13	0.15
Crude fat, %	5.86	6.57	5.36	5.84	5.69
Crude fiber, %	2.24	3.03	1.96	2.11	2.25
Total Ca, %	0.54	0.54	0.57	0.54	0.54
Total P, %	0.47	0.45	0.46	0.46	0.34
Available P, %	0.23	0.23	0.24	0.23	0.22
Standardized total tract digestible P, %	0.25	0.25	0.26	0.25	0.25

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^aCSBM = corn-soybean meal diets containing 0.15% synthetic lysine and no feed additive or co-products; DDGS = CSBM + 15% corn distillers dried grains with solubles diets; FW = CSBM + 8.59% thermally processed and dried supermarket food waste diets; SAA = corn-soybean meal diets with reduced crude protein + supplemental synthetic amino acids; PHY = corn-soybean meal diets containing 600 phytase units [FTU]/kg diet to release 0.11% standardized total tract digestible P.

Estimates for average daily BW gain from NRC (2012) were used to calculate the length of the feeding period (126 days), and average daily feed intake in each phase was used to calculate the total feed consumed per pig (294.4 kg; Table 2). Using the average diet composition (Table 1) and the feed consumption (Table 2), overall ingredient consumption per pig from 25 to 130 kg BW was calculated (Table 3) and used in the LCA.

Table 2.

Predicted average daily growth rate, feed intake, and days on feed of growing-finishing pigs in each growth phase from the NRC (2012) model

Measure	Phase 1	Phase 2	Phase 3	Phase 4	Total
Body weight, kg	25–50	50–75	75–100	100–130	–
Average daily gain, kg	0.759	0.900	0.917	0.873	–
Average daily feed intake, kg	1.583	2.230	2.637	2.916	–
Days on feed, day	34	29	28	35	126
Total feed intake, kg/pig	53.8	64.7	73.8	102.1	294.4

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Table 3.

Overall feed ingredient intake (kg) per growing-finishing pig^a during the 126-day feeding period.

Ingredient	Feeding program^b
Ingredient	CSBM	DDGS	FW	SAA	PHY
Corn	222.0	214.7	228.2	240.2	223.4
Distillers dried grains with solubles (DDGS)	0.0	44.2	0.0	0.0	0.0
Food waste	0.0	0.0	25.3	0.0	0.0
Soybean meal (SBM)	56.5	19.1	32.5	37.4	56.4
Choice white grease	8.7	7.7	0.0	8.3	8.1
Calcium carbonate	2.9	3.2	3.1	2.9	3.7
Monocalcium phosphate	1.9	1.7	2.0	2.2	0.2
Sodium chloride	1.0	1.0	1.0	1.0	1.0
Vitamin and trace mineral premix	0.9	0.9	0.9	0.9	0.9
L-lysine-HCl	0.4	1.4	1.0	1.1	0.5
L-Tryptophan	0.0	0.1	0.1	0.1	0.0
L-Threonine	0.1	0.3	0.2	0.3	0.1
DL-Methionine	0.0	0.1	0.1	0.1	0.0
Phytase	0.0	0.0	0.0	0.0	0.1
Total	294.4	294.4	294.4	294.4	294.4

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^aAssumed a pig needs to consume 294.4 kg of feed in 126 days to grow from 25 kg to 130 kg as predicted from the NRC (2012) model.

^bCSBM = corn-soybean meal diets containing 0.15% synthetic lysine and no feed additive or co-products; DDGS = CSBM + 15% corn distillers dried grains with solubles diets; FW = CSBM + 8.59% thermally processed and dried supermarket food waste diets; SAA = corn-soybean meal diets with reduced crude protein + supplemental synthetic amino acids; PHY = corn-soybean meal diets containing 600 phytase units [FTU]/kg diet to release 0.11% standardized total tract digestible P.

Estimation of nitrogen, and phosphorus excretion, and manure volatile solids production

The NRC (2012) growth model was used to estimate growth performance (average daily gain, average daily feed intake, and gain:feed), carcass composition (percentage of fat-free lean, carcass yield), and N, P, and C intake, retention, and excretion based on diet composition in each feeding program scenario. Estimated gross energy (GE) and ash content of each diet, along with the digestible energy (DE) coefficient (Noblet, 2007) and urinary energy (UE) as a fraction (assumed to be 0.02) of GE, were used to calculate the volatile solids (VS) produced in manure using the following equation (IPCC, 2019):

\begin{array}{l} V S = & [G E \times {(1 - D E % / 100)}_{} + (U E \times G E)] \\ \times [(1 - A S H) / 18.45] \end{array}

where VS = volatile solids excretion per day (on a dry organic matter basis); GE = gross energy intake (MJ per pig); DE = dry matter (DM) digestibility of the energy in the diet (%); UE = urinary energy expressed as a fraction of GE (assumed to be 0.02); ASH = the ash content of manure calculated as a fraction of the DM feed intake; 18.45 = approximate conversion factor for dietary GE per kg of DM (MJ/kg). The DE was calculated based on the ratio between the estimated value of GE and DE, which corresponds to the digestibility coefficient of energy (Noblet, 2007).

Spatially explicit regions

We chose to evaluate the diets using the same feeding programs in the three different geographic regions (Midwest, Mid-Atlantic, and Southwest) where most of the pork production occurs in the United States (Figure 1) to objectively compare spatially explicit environmental impacts among regions without the confounding effects of using diets with different ingredient composition and environmental impacts. Although the types, quantities, and cost of feed ingredients vary among geographic regions in the United States, and significant differences in diet composition occur among regions when formulating least-cost diets, we chose not to formulate regional diets in this study on a least-cost basis because of the added complexity and lack of spatially explicit price data for all ingredients used in the diets. The Midwest is the predominant pork production region in the United States with 54.95 million hogs (76%) marketed annually, followed by 11.03 million hogs (15%) marketed in the Mid-Atlantic region, and 4.66 million hogs (6%) marketed in six states in the Southwest region, which collectively represent 97.65% of all U.S. pork production. The gray shaded states in Figure 1 represent the “Other” region where the remaining 1.74 million hogs are produced (2% of total) in the United States

Figure 1. — States comprising different geographic regions used in LCA determinations of feeding programs.

Environmental impacts of dietary ingredients

Corn, soybean meal, and DDGS were the main ingredients of interest for assessing the environmental impacts of swine feeding programs in this study because they are the most used in United States swine diets and are the major contributors to GHG emissions, water consumption, and land use associated with commercial pork production systems. The environmental impacts of these ingredients were based on a spatially explicit, FoodS³ model of corn, soybeans, DDGS, and soybean meal movement in the United States (Smith et al., 2017; Brauman et al., 2020). This FoodS³ model links counties of feed production to counties of animal production, directly or indirectly via intermediate feed processors, through a least cost transport optimization model which enables more detailed and accurate estimates of feed flows compared with more general estimates used in other LCA studies (Smith et al., 2017; Brauman et al., 2020). Furthermore, the FoodS³ model includes county-level GHG impacts from cradle-to-feed gate (i.e., from raw material extraction of all inputs through feed production) for corn and soybean production (Pelton et al, 2021; Brauman et al., 2020). Environmental impacts from the dietary inclusion of DDGS were based on accounting for the emissions produced in the ethanol production process; emissions, water consumption and land embedded in corn production and allocated to DDGS (based on relative energy content of ethanol and DDGS co-products of approximately 40.1%); and the emissions from the additional energy required to dry the distiller grains with solubles. Environmental impacts from the production of soybean meal were similarly considered and based on the relative energy content of soybean oil and soybean meal co-products of about 62.6%. For FW, emissions were estimated based on the assumption that the food waste was processed in the United States using an average mix of dehydration processes, including steam heating and drying, based on inventories provided by Ogino et al. (2007),Ogino et al. (2007). The LCA impacts of the crystalline amino acids, phytase, and other micro ingredients used in diets were not considered in this analysis because these ingredients were expected to be minor contributors to environmental impacts compared with the primary ingredients of corn, soybean meal, and DDGS that make up about 95% of the diet. In addition, there were minimal differences in dietary inclusion rates of each of these micro ingredients across feeding programs (Table 3), thereby allowing their exclusion from the comparative analysis.

In addition to GHGs, the FoodS³ model was used to estimate water consumption from irrigated water use attributed to corn and soybean production (Brauman et al. 2020), and land use at the county level using the inverse of the average yields from 2007 to 2017 for each crop (USDA NASS, 2018; Pelton et al 2021). The embedded land use and water consumption impacts associated with crop inputs were not included in these analyses because their contributions are relatively small compared with cropland requirements per unit of output. These production-based impacts of feed were connected to county hog production demands based on total quantities sourced between origin and destinations.

Environmental impacts of manure management

In addition to feed inputs, manure management is another major contributor to GHG emissions. To account for manure management at a county scale, we used the methodology described by Pelton (2016) where it was assumed that county-level manure management reflected state-level manure management types due to data availability limitations at more granular scales. Manure management distributions were altered to account for counties that have documented usage of anaerobic digesters and are operationally based on information provided by the EPA’s AgSTAR Livestock Anaerobic Digester Database (https://www.epa.gov/agstar/livestock-anaerobic-digester-database). For the anaerobic digester systems, the methane captured was assumed to be either flared (i.e., combusted without energy recovery), converted to thermal energy and/or electricity typically for use on the farm with excess sold to the grid, or upgraded to renewable natural gas for pipeline injection, and were dependent on overall collection and destruction efficiency assumptions (Pelton 2016).

Emissions for manure were calculated based on N and VS concentrations of diets in each feeding program evaluated using a LCA approach. The quantity of VS and N produced throughout each successive feeding phase during the entire 126-day grower-finisher period was integrated to represent a market hog mass of 130 kg (Thoma, et al., 2011). Total VS excreted over the lifetime of the hog was then combined with average county ambient temperatures, the maximum methane generation potential (assumed to be 0.48, and 0.432 for digesters), the altered-county manure management system distributions, and associated methane conversion factors to estimate total methane emissions. Direct and indirect N₂O was also estimated based on total N excreted over the lifetime of the market hog, and direct and indirect emissions rates associated with each management system and region (in the case of indirect leaching-related N₂O). In addition, following best practice methods, a portion of the manure emissions generated over the lifetime of breeding sows was allocated to each market hog produced based on the average number of litters per sow per year and state-specific average number of piglets per litter, which were assumed to be approximately 3.5 litters and U.S. average of 10.6 (range from 5 to 11.6) piglets per litter, respectively (Thoma et al., 2011; USDA NASS, 2018). Due to the lack of data regarding inter-county transport of pigs within different growing stages, all total lifetime manure production was assumed to be handled in the county in which the hog was finished prior to transporting to slaughter facilities.

Avoided impacts

In this assessment, along with the avoided impacts from energy production from anaerobic digestion of manure, where avoided marginal grid emissions and natural gas emissions were considered for counties utilizing biogas, GHG emissions avoided from the prevention of food waste in landfills were also considered. Food waste disposed in landfills is one of the primary contributors to waste-related GHG emissions. By utilizing the food waste as a feed ingredient in our LCA analyses, a portion of these emissions would be prevented by diverting food waste away from landfills. However, because of limited spatial information on how landfilled food waste emissions vary across regions, we instead rely on the U.S. EPA WARM model assumptions of a landfilled composite food waste mix (meats and other foods) to estimate a net avoided the emission of 700 kg CO₂ equivalent per short ton (907 kg) of food waste diverted from landfills (EPA, 2020). This estimate includes the transportation of food waste to the landfill, methane emissions from landfilling, and carbon savings from landfill carbon storage.

Various studies have considered the avoided emissions from the use of DDGS or other alternative ingredients in feed formulations to replace corn and soybean meal, assuming that avoided demand in feed results in less corn and soybeans produced. However, we used a more conservative approach and assumed that any shifts in U.S. domestic feed demand for corn and soybean meal would likely not displace actual production, but rather lead to greater U.S. exports of these commodities.

Results

Feed formulation

The relative amounts of corn and soybean meal used in diets varied considerably among feeding programs, with the greatest amount of corn expected to be consumed by growing-finishing pigs from the SAA feeding program, and the greatest amount of soybean meal expected to be consumed for the CSBM and PHY feeding programs (Table 3). The relative differences in total corn and soybean meal consumption among feeding programs were the main factors affecting GHG emissions, water consumption, and land use impacts attributed to feeding.

Estimated nitrogen and phosphorus intake, retention, and excretion

Estimates of N, P, and C intake, retention, and excretion from each diet in each of the five 4-phase feeding programs during the entire growing-finishing feeding period were obtained from the NRC (2012) model (Table 4). The amount of N intake per pig was less for DDGS (6.09 kg), FW (6.25 kg), and SAA (5.83 kg) feeding programs compared with CSBM (6.85 kg) and PHY (6.86 kg) programs. Because N retention among feeding programs was assumed to be equal in the model due to meeting amino acid requirements, the percentage of N retention relative to N intake was greater (42.2–45.3%), and N excretion was reduced (3.19–3.61 kg/pig) in the DDGS, FW, and SAA feeding programs compared with the CSBM and PHY feeding programs (38.5% and 4.21 kg/pig, respectively).

Table 4.

Estimated nitrogen, phosphorus, and carbon intake, retention, and excretion per growing-finishing pig from 25 to 130 kg body weight for each feeding program predicted from the NRC (2012) model^a

Measure	Feeding program^b
Measure	CSBM	DDGS	FW^c	SAA	PHY
Nitrogen
Intake and wastage, kg/pig	6.85	6.09	6.25	5.83	6.86
Retention, % of intake	38.5	43.3	42.2	45.3	38.5
Excretion, kg/pig	4.21	3.45	3.61	3.19	4.22
Phosphorus
Intake and wastage, kg/pig	1.381	1.315	1.347	1.352	1.001
Retention, % of intake	32.0	33.6	32.8	32.7	44.2
Excretion, kg/pig	0.939	0.873	0.905	0.910	0.559
Carbon
Intake and wastage, kg/pig	111.8	112.3	111.2	111.4	111.9
Retention, % of intake	30.1	29.9	30.2	30.2	30.0
Excretion, kg/pig	78.2	78.7	77.6	77.8	78.3

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^a NRC (2012) model assumed nutrient retention (kg/d or kg/pig) is only determined by nutrient requirements and is the same across all diets.

^cCarbon in supermarket food waste was calculated using and equation from NRC (2012) feed ingredient library where carbon = crude protein × 0.53 + crude fat × 0.76 + starch × 0.44 +(lactose + sucrose, raffinose + stachyose + verbascose) × 0.42 + (organic residue-raffinose-stachyose + verbascose) × 0.45; unknown nutrients were left as blank; organic residue was calculated as ADF + NDF.

Phosphorus intake per pig varied among feeding programs (Table 4) and was greatest for CSBM (1.381 vs. 1.001 to 1.352 kg/pig). Similar to N retention, equal P retention was assumed in the NRC (2012) model resulting in slightly greater P retention as a percentage of P intake for the DDGS feeding program (33.6%) compared with the CSBM (32.0%), FW (32.8%), and SAA (32.7%) feeding programs. The FW and SAA feeding programs also had slightly reduced (2.5 and 2.1%, respectively) P intake and excretion (3.6% and 3.1%, respectively) compared with CSBM. However, the greatest reduction in P intake (23.9% to 27.5%) and excretion (36.0% to 40.5%) was for PHY because of the increased contributions of digestible P from corn and soybean meal that occurs from the use of phytase to improve P digestibility. In contrast to the differences observed for N and P balance among feeding programs, there were no substantial differences in C intake, retention, or excretion (Table 4).

Estimated volatile solids excretion

Total VS excretion per growing-finishing pig was estimated to be the greatest when feeding the DDGS diets (42.71 kg/pig) and the least for feeding the FW diets (34.44 kg/pig) compared with the other feeding programs (Table 5).

Table 5.

Estimated volatile solid (VS) excretion per growing-finishing pig from 25 to 130 kg body weight for each feeding program^a

Measure	Feeding program^b
Measure	CSBM	DDGS	FW	SAA	PHY
VS, kg/pig/day	0.30	0.34	0.27	0.29	0.30
Total VS excretion, kg/pig	37.79	42.71	34.44	37.02	37.95

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^aAssuming a pig consumes 294.4 kg of feed in 126 days to grow from 25 kg to 130 kg predicted from the NRC (2012) model.

Environmental impact factors for feed ingredients among regions

Greenhouse gas emissions, water consumption, and land use were estimated for each major feed ingredient (i.e., corn, soybean meal, DDGS, and food waste) and for each geographic region. These impact factors represent embedded consumption-based environmental impacts consumed by the pork production sector and production-based impacts of swine feed ingredient production, both estimated using the spatially explicit database in the FoodS³ model (Table 6). The GHG emissions, water, and land use differed among feeding programs depending on the amounts of corn and soybean meal in diets (Table 3), with a regional average standard deviation across diet types of 8 kg CO₂ equiv, 0.8 m³, and 27 m² per market hog, respectively. In addition, differences in regional supply chains and associated variation in impacts from corn and soybean meal production had the greatest effect on GHG emissions, water consumption, and land use for each diet, with an average diet standard deviation across regions of 33 kg CO₂ equiv., 24 m³, and 174 m², respectively.

Table 6.

Consumption- and production-based Life Cycle Assessment environmental impact factors (per kg of feed ingredient) of major feed ingredients used in diet formulation of feeding programs ^a.

Region	Ingredient	GHG^b (kg CO₂ equiv./kg)	Water consumption (m³/kg)	Land use (m²/kg)
Midwest	Corn	0.507 [0.476]	0.017 [0.0004]	1.054 [1.031]
	Soybean meal	0.975 [0.948]	0.021 [0.033]	2.279 [2.357]
	DDGS^c	1.041 [1.010]	0.011 [0.020]	1.383 [1.419]
	Food waste	0.413	0	0
Mid-Atlantic	Corn	0.772 [0.864]	0.006 [0.001]	1.244 [1.318]
	Soybean meal	1.380 [1.776]	0.014 [0.025]	3.104 [3.832]
	DDGS	1.193 [2.151]	0.007 [0.0003]	1.578 [1.744]
	Food waste	0.413	0	0
Southwest	Corn	0.701 [0.539]	0.232 [0.210]	1.185 [1.086]
	Soybean meal	1.253 [0.995]	0.210 [0.265]	3.125 [2.596]
	DDGS	1.227 [1.326]	0.160 [0.189]	1.391 [1.969]
	Food waste	0.413	0	0
Other	Corn	0.775 [0.729]	0.046 [0.013]	1.313 [1.273]
	Soybean meal	1.211 [1.166]	0.095 [0.032]	2.616 [3.194]
	DDGS	1.380 [1.556]	0.042 [0.068]	1.712 [1.912]
	Food waste	0.4133	0	0
Total	Corn	0.571 [0.519]	0.029 [0.012]	1.101 [1.059]
	Soybean meal	1.062 [1.003]	0.033 [0.033]	2.469 [2.469]
	DDGS	1.087 [1.019]	0.020 [0.020]	1.425 [1.007]
	Food waste	0.413	0	0

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Consumption based estimates (top number) are for feed consumed by swine in the listed U.S. geographic region, while the bracketed numbers are the production-based emission factors associated with crop production in each region

^aEstimates for crop production region are shown in [].

^bGHG = greenhouse gases.

^cDDGS = corn distillers dried grains with solubles.

Compared with corn, soybean meal had the greatest GHG (0.571 vs. 1.062 kg CO₂ equiv./kg), water consumption (0.29 vs. 0.33 m³/kg), and land use (1.101 vs. 2.469 m²/kg) footprint across all regions, except for 9.5% less water consumption in the Southwest region (Table 6). Soybean meal also had a greater impact on water consumption and land use across all regions than DDGS, but GHG emissions for soybean meal were slightly less than for DDGS in the Midwest (0.975 vs. 1.041 kg CO₂ equiv./kg) and the Other minor pork production states (1.211 vs. 1.380 kg CO₂ equiv./kg). Food waste was estimated to have the least GHG emissions (0.413 kg CO₂ equiv./kg) due to the avoided emissions from landfill disposal, with no effect on water consumption and land usage in all regions (Table 6). Therefore, food waste had the least GHG emissions, water consumption, and land use than all other feed ingredients evaluated in this study.

The Midwest region had the least GHG emissions, water consumption, and land use for corn, soybean meal, and DDGS production (Table 6), which resulted in the least impacts from feed consumption from hogs produced in the Midwest because according to the FoodS³ model, >99% of the total demand of these three ingredients are sourced from the Midwest (Table 7). The Southwest region had less GHG emissions for corn (0.701 kg CO₂ equiv./kg) and soybean meal (1.253 kg CO₂ equiv./kg) compared with corn (0.772 kg CO₂ equiv./kg) and soybean meal (1.380 kg CO₂ equiv./kg) in the Mid-Atlantic region, but the Southwest had slightly greater GHG emissions for DDGS (1.227 kg CO₂ equiv./kg) than the Mid-Atlantic region (1.193 kg CO₂ equiv./kg; Table 6). Pork production systems in the Southwest region source 69% of total corn consumed from the Midwest region (30% from the Southwest; Table 7), while swine farms in the Mid-Atlantic region source only 39% of total corn used from the Midwest (47% from the Mid-Atlantic; Table 7). These differences resulted in less GHG emissions associated with corn used for feed in pork production in the Southwest region compared with those in the Mid-Atlantic region (Table 6). The Mid-Atlantic soybean production region has the greatest emissions from soybean meal (1.380 kg CO₂ equiv./kg) associated with the pork production sector (Table 6). Swine production systems in the Southwest source 100% of their soybean meal from Midwest soybeans, whereas swine operations in the Mid-Atlantic region source only 55% of their soybean meal from the Midwest (about 40% from the Mid-Atlantic), resulting in less overall GHG emissions for soybean meal in the Southwest states compared with Mid-Atlantic states (Table 7). For DDGS, swine farms in both the Southwest and Mid-Atlantic regions source about 97% of the DDGS used in swine diets from the Midwest, with the remaining 3% of the DDGS is sourced from within each of the respective Southwest and Mid-Atlantic regions (Table 7).

Table 7.

Proportion of corn, soybean meal, and corn distillers dried grains with solubles (DDGS) sourced from each region to produce market hogs in each region based on the FoodS³ model

Hog production region	Ingredient	Feed ingredient production region
Hog production region	Ingredient	Midwest %)	Mid-Atlantic (%)	Southwest (%)	Other (%)
Midwest	Corn	>99	<1	0	0
	Soybean meal	>99	<1	0	0
	DDGS	100	0	0	0
Mid-Atlantic	Corn	39	47	0	14
	Soybean meal	55	39	0	6
	DDGS	97	3	0	0
Southwest	Corn	69	0	30	<1
	Soybean meal	100	0	0	0
	DDGS	97	0	3	0
Other	Corn	28	16	4	52
	Soybean meal	73	8	11	8
	DDGS	77	2	1	20
Total	Corn	86	8	2	4
	Soybean meal	92	6	<1	1
	DDGS	99	1	<1	1

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The Southwest region had much greater water consumption attributed to corn (0.232 m³/kg), soybean meal (0.210 m³/kg), and DDGS (0.160 m³/kg) compared with the Midwest and Mid-Atlantic regions (Table 6). In contrast, the Mid-Atlantic pork production region had the greatest land use attributed to corn (1.244 m²/kg) and DDGS (1.578 m²/kg) compared with all other regions (Table 6).

Effect of feeding program and region on GHG emissions

The FW feeding program had the least GHG emissions from feed (175.2 kg CO₂ equiv./market hog), manure (144.6 kg CO₂ equiv./market hog), and overall impacts (319.9 kg CO₂ equiv./market hog), while the SAA program had the next least contribution to GHG emissions from feed (176.8 kg CO₂ equiv./market hog), manure (147.8 kg CO₂ equiv./market hog), and overall impacts (324.6 kg CO₂ equiv./market hog) compared with the other feeding programs regardless of region (Table 8). Reducing the CP content of diets by using synthetic amino acids to meet the SID amino acid requirements of pigs allows for a substantial reduction in soybean meal use which results in increased corn use (Table 3) that has less GHG emission intensity. In contrast, the DDGS feeding program resulted in the greatest GHG emissions from feed (190.9 kg CO₂ equiv./market hog), manure (163.2 kg CO₂ equiv./market hog), and overall average impact (354.1 kg CO₂ equiv./market hog) among regions compared with the other feeding programs. The CSBM and PHY feeding programs had intermediate and similar GHG emissions among feeding programs due to similar diet composition.

Table 8.

Weighted U.S. average greenhouse gas emissions (kg CO₂ equiv./market hog) from feed, manure, and overall impacts among swine grower-finisher feeding programs and swine production geographic regions

Region	Feeding program^a
Region	CSBM	DDGS	FW	SAA	Phytase
Feed
Midwest	166.6	173.5	157.8	158.2	168.2
Mid-Atlantic	247.9	244.9	231.6	237.1	250.4
Southwest	225.1	228.8	211.2	215.3	227.4
Other	238.9	250.5	226.7	231.5	241.5
Average	185.6	190.9	175.2	176.8	187.4
Manure
Midwest	115.4	121.9	108.1	111.1	115.7
Mid-Atlantic	305.0	325.1	288.5	290.0	305.8
Southwest	233.4	249.8	219.5	227.7	234.0
Other	196.9	208.9	185.2	189.6	197.4
Average	153.9	163.2	144.6	147.8	154.3
Overall
Midwest	282.0	295.4	265.9	269.3	284.0
Mid-Atlantic	552.9	570.0	520.1	527.1	556.1
Southwest	458.5	478.6	430.7	443.1	461.4
Other	435.9	459.4	411.9	421.1	438.9
Average	339.5	354.1	319.9	324.6	341.7

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There were substantial differences in GHG emissions attributed to feeding program and manure across geographic regions (Table 8). The feeding program contributed more to GHG emissions on average across the United States regardless of program type, compared with manure emissions. However, while the Midwest and Other regions reflect this relationship, Mid-Atlantic and Southwest regions conversely showed slightly greater GHG emissions contributions from manure across feeding programs. Swine farms in the Midwest region had both the least emissions from feed (157.8–173.5 kg CO₂ equiv./market hog), regardless of feeding program, and the least manure emissions per market hog (108.1–121.9 kg CO₂ equiv./market hog), which resulted in the least overall combined impact (265.9–295.4 kg CO₂ equiv./market hog) on GHG emissions compared with other regions. Manure emissions were much greater for the Mid-Atlantic region (288.5–325.1 kg CO₂ equiv./market hog) compared with all other regions.

Effect of feeding program and region on water consumption

Small differences in water consumption per market hog produced were observed among feeding programs within each region (Table 9). Water consumption per market hog was similar for the FW (7.64 m³/market hog) and DDGS (7.70 m³/market hog) feeding programs, which were slightly less compared with the other feeding programs (8.15–8.30 m³/market hog). The CSBM and PHY feeding programs had the greatest water consumption impacts because these diets contained the greatest amount of corn and soybean meal among the feeding programs.

Table 9.

Weighted U.S. average water consumption (m³/market hog) associated with production of feed ingredients used in swine grower-finisher feeding programs based on pork production geographic region

Region	Feeding program^a
Region	CSBM	DDGS	FW^b	SAA	Phytase
Midwest
Corn	3.67	3.58	3.80	4.00	3.72
Soybean meal	1.16	0.39	0.67	0.77	1.16
DDGS	0	0.48	0	0	0
Total	4.83	4.45	4.47	4.77	4.88
Mid-Atlantic
Corn	1.36	1.33	1.41	1.49	1.38
Soybean meal	0.76	0.26	0.44	0.51	0.76
DDGS	0	0.32	0	0	0
Total	2.12	1.91	1.85	1.99	2.14
Southwest
Corn	50.93	49.70	52.82	55.60	51.71
Soybean meal	11.88	4.02	6.84	7.87	11.86
DDGS	0	7.07	0	0	0
Total	62.81	60.79	59.66	63.47	63.58
Other
Corn	10.14	9.89	10.51	11.07	10.29
Soybean meal	5.37	1.81	3.09	3.55	5.36
DDGS	0	1.84	0	0	0
Total	15.51	13.55	13.60	14.62	15.65
Overall
Corn	6.32	6.17	6.56	6.90	6.42
Soybean meal	1.89	0.64	1.08	1.25	1.88
DDGS	0	0.89	0	0	0
Total	8.21	7.70	7.64	8.15	8.30

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^bNo water usage value was assigned to food waste in any region.

In contrast, there were dramatic differences in water consumption per market hog attributed to feeding program among geographic regions (Table 9). Water consumption per market hog from feeding programs in the Southwest region was more than 30 times greater than in the Mid-Atlantic region, and about 13 times greater than in the Midwest region. Water consumption attributed to a feeding program in Midwest states was 2.3 times greater than in the Mid-Atlantic states.

Effect of feeding program and region on land use

Feeding diets containing 8.6% food waste had the greatest impact on reducing land use per market hog (331.5 m²), followed by feeding the 15% DDGS diets (346.5 m²/market hog), regardless of geographic region (Table 10). The SAA feeding program also resulted in less land use per hog marketed (356.8 m²) compared with the CSBM (381.7 m²/market hog) and PHY (385.2 m²/market hog) feeding programs. Land use impacts for corn, soybean meal, and DDGS were the least in the Midwest region, with Mid-Atlantic and Southwest regions having an average of 22.8% and 18.7% greater impact, respectively, compared with the Midwest states (Table 10).

Table 10.

Weighted U.S. average land use (m²/market hog) associated with feed ingredient production that were used in swine grower-finisher feeding programs based on pork production geographic region

Region	Feeding program^a
Region	CSBM	DDGS	FW^b	SAA	PHY
Midwest
Corn	231.9	226.3	240.5	253.2	235.5
Soybean meal	128.7	43.5	74.1	85.2	128.5
DDGS	0	61.1	0	0	0
Total	360.6	330.9	314.6	338.4	364.0
Mid-Atlantic
Corn	273.7	267.2	283.9	298.9	278.0
Soybean meal	175.4	59.3	100.9	116.1	175.1
DDGS	0	61.5	0	0	0
Total	449.1	396.2	384.8	415.0	453.1
Southwest
Corn	260.7	254.4	270.4	284.7	264.8
Soybean meal	176.5	59.7	101.6	116.9	176.2
DDGS	0	75.6	0	0	0
Total	437.3	375.6	372.0	401.5	441.0
Other
Corn	288.8	281.9	299.6	315.4	293.3
Soybean meal	147.8	50.0	85.0	97.8	147.5
DDGS	0	75.6	0	0	0
Total	436.6	407.5	384.6	413.2	440.8
Overall
Corn	242.2	236.4	251.2	264.4	245.9
Soybean meal	139.5	47.2	80.3	92.4	139.3
DDGS	0	63.0	0	0	0
Total	381.7	346.5	331.5	356.8	385.2

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^bNo land usage value was assigned to food waste in any region.

Discussion

General overview

The U.S. ranks among the top six countries responsible for most of the global environmental impacts from agriculture (West et al., 2014; FAO, 2022). Therefore, if intervention opportunities can be identified in key agricultural commodity supply chains such as corn, soybeans, and pork, effective mitigation strategies can be implemented to minimize these impacts. Unfortunately, only a few peer-reviewed LCA studies have been conducted to assess the environmental impacts of pork production in the United States (Halberg et al., 2010; Pelletier et al., 2010; Stone et al., 2012), and all were conducted more than a decade ago.

Andretta et al. (2021) conducted a recent comprehensive literature review of 55 published LCA studies involving pork production systems in various countries that at a minimum, estimated climate change impacts. Results from these studies confirmed that swine feed (including crop cultivation, manufacturing processes, and transportation) was the primary contributor to the environmental impacts of pork production systems around the world. However, although feed is the most important contributor to the total environmental impacts of pig production, detailed descriptions of LCAs of feed ingredients were presented in only 9% of the publications, specific diet formulations were provided in 38% of the publications, and nutritional composition of diets was provided in only 29% of the papers reviewed. This information is essential for accurately comparing LCA results across studies and alternative feed formulations. Therefore, a detailed description of diet composition and feed ingredient LCA assumptions used in this study were provided in Tables 1 and 3. The focus of the LCA evaluation in this study was on three core environmental impacts: GHG emissions, water consumption, and land use in the grower-finisher phase of production (25–130 kg BW) because this phase represents about 75% of total feed usage in farrow-to-finish swine operations. The N, P, and C utilization efficiency estimates of diets and feeding programs were also provided because planetary boundaries of these nutrients have been exceeded (Gerber et al., 2014; Sutton et al., 2019; Li et al., 2019), and identifying feeding programs that contribute the least to N, P, and C waste can reduce these negative impacts.

Corn DDGS is the most abundant and widely used co-product in U.S. swine diets where it partially replaces a portion of corn, soybean meal, and inorganic phosphate to reduce diet cost while supporting satisfactory growth performance and carcass characteristics at dietary inclusion levels up to 20% (Jang et al., 2021; Buenavista et al., 2021). However, the relatively high CP content (27%) relative to the standardized ileal digestible lysine content (0.55%), and amino acid imbalances in DDGS diets require supplementation of several synthetic amino acids including L-lysine HCl, L-threonine, L-tryptophan, L-valine, and L-isoleucine to achieve optimal growth performance and carcass composition while minimizing excess N excretion in manure (Cemin et al., 2019; Wellington et al., 2018; Kwon et al., 2020; Kerkaert et al., 2021). The relatively high standardized total tract digestible P content (DM basis; NRC, 2012) in DDGS (0.44%) compared with corn (0.10%) and soybean meal (0.38%) reduces the need for supplemental inorganic phosphate in swine diets which can reduce P intake and excretion in manure.

Upcycling pre- and post-consumer food waste into animal feed using dehydration and proper thermal processing is an emerging opportunity in a circular food system to recapture and repurpose carbon (energy), N, and P for productive purposes while also reducing the negative environmental impacts from disposal in landfills (Shurson, 2020). Results from a recent study (Fung et al., 2019b) showed that dehydrated and thermally processed food waste containing fruit, vegetables, meat, and dairy products from supermarkets can provide ME (4,922 kcal/kg DM) concentrations greater than found in corn (3,875 kcal/kg DM), standardized ileal digestibility (87–96%) of indispensable amino acids comparable to that of soybean meal, and a substantial amount of standardized total tract digestible P (0.31%, as-fed basis). Additional studies also showed ME, digestible amino acids, and digestible phosphorus concentrations comparable to concentrations found in common corn-soybean meal diets fed to growing-finishing pigs (Fung et al., 2019a; Jinno et al., 2018). Thermal processing of food waste at 100 °C for 30 min is required before feeding to swine in the United States, which has been shown to be effective in destroying parasites (Trichinella spiralis, Toxoplasma gondii), bacteria (Salmonella, Escherichia coli), and viruses (African swine fever virus, Classical swine fever virus, highly pathogenic avian influenza virus H5 and H7, Newcastle disease virus, Foot-and-mouth disease virus). Unfortunately, because of historical experiences of feeding uncooked “garbage” to pigs and disease outbreaks associated with that practice, the adoption of this high impact, environmental sustainability strategy has been slow due to current federal and state regulations, and the lack of education, acceptance, and industry infrastructure to support the adoption of this practice in the United States (Shurson, 2020; Dou et al., 2021).

Nitrogen, phosphorus, and carbon balance

Quantitative estimation of nutrient balance in feed and animal production systems is necessary to determine the extent of nutrient cycling and identify areas on various spatial scales where interventions are needed (Sharara et al., 2022). Nutrient balance accounting can be conducted in any system with defined boundaries and where nutrient imports and exports can be measured at any level of scale (e.g., field, whole farm, watershed, and state) to assess imbalances (Sharara et al., 2022).

Nitrogen utilization efficiency

The DDGS, FW, and SAA feeding programs had less than expected N intake per market hog than the CSBM and PHY programs because all diets were formulated on a SID AA basis that reduces dietary CP concentrations and increases the use of supplemental crystalline amino acids to meet the essential amino acid requirements of pigs in each diet phase. In general, for each one percentage unit decrease in dietary CP concentration, N excretion is decreased by about 10%, assuming that adequate synthetic amino acids are supplemented in the diet to meet the amino acid requirements of pigs (Kerr, 2003). The addition of synthetic amino acids to swine diets is a common feed formulation approach to reduce the amount of CP (N) content resulting from using reduced amounts of high protein feed ingredients (e.g., soybean meal) to meet the digestible amino acid needs (NRC, 2012), while reducing diet cost, N excretion in manure (Cappelaere et al., 2021), and potentially improving gastrointestinal health of pigs (Luise et al., 2021).

About 54% of nitrogen present in swine diets is not utilized for growth and lean deposition and is excreted in feces and urine (Millet et al., 2018). Equal N retention among diets and feeding programs was assumed in the NRC (2012) model because all nutrient requirements were met, and no excesses or deficiencies of N were expected relative to pig requirements. As a result, the percentage of N retention relative to N intake was improved, and N excretion was reduced for the DDGS, FW, and SAA feeding programs compared with CSBM and PHY feeding programs. Although it may seem counterintuitive that the CSBM and PHY feeding programs had less N retention as a percentage of intake compared with the other feeding programs, this occurred because of greater amounts of synthetic amino acids added to DDGS, FW, and SAA diets which reduced N intake.

Although LCA impacts of some synthetic amino acids, such as L-lysine HCl, L-threonine, and DL-methionine have been estimated (Marinussen and Kool, 2010), LCA estimates have not been determined for L-tryptophan. Therefore, because of the lack of LCA data for L-tryptophan and the minor contributions provided by small amounts of supplemental synthetic amino acids toward GHG emissions, land use, and water consumption, these LCA impacts were excluded in the analysis of feeding programs in this study.

Phosphorus utilization efficiency

The use of highly digestible sources of P, formulating swine diets based on STTD of P requirements, and adding phytase are common strategies used to reduce P concentration in swine manure. Estimated P intake per pig varied among feeding programs and was greatest for CSBM diets. All diets evaluated in this study were formulated using STTD of P values for corn, soybean meal, DDGS, and food waste to meet the digestible P requirement of pigs in each diet phase, which resulted in differences in total P intake among feeding programs. Because DDGS contains a greater concentration of total and digestible P than corn and soybean meal (NRC, 2012), diets in the DDGS feeding program contained less monocalcium phosphate, less total P intake, similar P retention, and less P excretion in manure than when feeding CSBM diets. However, Hanson et al. (2012) reported that although feeding CSBM diets containing 20% or 30% DDGS resulted in decreased DM digestibility and fecal P concentration compared with feeding CSBM diet with no DDGS, total P excretion and retention was not affected by dietary DDGS inclusion rate.

As expected, the greatest reduction in P intake and excretion was observed for the PHY feeding program because of the substantial reduction in supplemental monocalcium phosphate added to diets resulting from phytase release of a significant proportion of P bound to phytate in corn and soybean meal to meet the P requirement while also reducing P excretion. The addition of phytase to swine diets has been shown to increase P digestibility by 20–50% which subsequently reduces P excretion in manure (Selle and Ravindran, 2008; Humer et al., 2015; Lautrou et al., 2021). The use of Ronozyme P5000 CT phytase to reduce the amount of inorganic phosphate supplementation in swine diets has been shown to reduce GWP by 17%, acidification potential (AP) by 110%, and eutrophication potential (EP) by 700% (Nielsen and Wenzel, 2007). Although AP and EP were not estimated in the current study, the dramatic reduction in EP is consistent with the estimated reduction in manure P excretion per grower-finisher pig from adding phytase to CSBM diets in the current study.

Kebreab et al. (2016) conducted an LCA to determine the environmental impacts of three swine diet formulation scenarios including standard base diets without or with supplemental synthetic amino acids, and a standard base diet supplemented with synthetic amino acids and phytase used in large-scale production systems in Europe, North America, and South America. System boundaries included all processes up to the farm gate on a live body weight basis. Eutrophication potential was reduced by 35% by feeding synthetic amino acids and phytase, but the contribution from phytase was minimal (3%) because nitrogenous compounds dominated the contribution to EP and the assumption that soil P content did not exceed the capacity for crop uptake and the reduction of P in manure would be compensated using inorganic fertilizer. Kebreab et al. (2016) also reported that feeding the amino acid supplemented diets with or without phytase also provided significant benefits for reducing AP.

Carbon utilization efficiency

Assessing carbon balance and diet digestibility in animal feeding programs is important because it relates to carbon dioxide and methane emissions and the need to find strategies to sequester carbon and reduce these emissions. In the current study, dietary C concentrations were similar (average of 38%), resulting in similar C intake, retention, and excretion estimates among feeding programs. These results are similar to those reported by Trabue et al. (2022) where no differences were observed in dietary C concentration (39.0–40.3%) or mass balance (98–113% of C consumed) between pigs fed low fiber diets consisting of CSBM and high fiber diets containing 28% DDGS. However, swine diets containing high-fiber ingredients, such as DDGS, have less dry matter digestibility compared with low-fiber diets (Agyekum and Nyachoti, 2017). As such, Trabue et al. (2022) showed that pigs fed the high fiber diets had greater excretion of total solids, C, N, and organic N in manure, and greater concentrations of ammonia, sulfide, volatile fatty acids, and phenols in manure than pigs fed low fiber diets, all of which have negative environmental consequences.

Environmental impact factors for feed ingredients among regions

The GHG emissions, water consumption, and land use differed across feeding programs depending on the amounts of corn and soybean meal used in diets. Soybean meal had the greatest GHG, water consumption, and land use footprint across all regions, except for slightly less water consumption in the Southwest region because of the comparatively reduced yields for soybeans associated with the pork production sector (2007–2017 average of 3,060 kg/ha for soybeans versus 9,445 kg/ha for corn), the relatively high land use change compared with corn (Pelton et al., 2021), and the additional processing required to produce soybean meal feed from soybeans. Soybean meal also had a greater water consumption and land use impact across all regions than DDGS due to reduced yields of soybeans compared with corn used to produce DDGS.

Food waste was estimated to have the least GHG emissions of all major ingredients due to the avoided emissions from landfill disposal, with no effect on water consumption and land usage in all regions. Although water consumption and land use can be estimated for thermally processed food waste, it was excluded from the scope of this study because water consumption and land usage that can be attributed to food waste use in diets are negligible compared with water consumption associated with crop production (i.e., corn and soybeans), which represents 92% of global water consumption (Hoekstra et al., 2012). As a result, food waste had the least GHG emissions, water consumption, and land use than all other feed ingredients evaluated in this study.

As expected, the Midwest pork production region had the least GHG emissions, water consumption, and land use for corn, soybean meal, and DDGS because of the high yields and efficient crop production. Furthermore, our FoodS³ model is based on Midwest pork producers sourcing nearly all of their feed ingredients from the Midwest, which is a major benefit from co-locating pork production systems near efficient crop production. Our model also indicates that pork production systems in the Southwest region source 69% of their total corn from the Midwest region, while the Mid-Atlantic region (which has the greatest GHG intensity for corn production) sources only 39% of total corn from the Midwest. Consequently, overall GHG emissions were less for hogs produced in the Southwest region compared with those in the Mid-Atlantic.

Similarly, for soybean meal, the relatively less GHG emission intensity from Midwest soybean production and high within region feed sourcing resulted in the least GHG emission intensity from soybean meal in the Midwest. Our FoodS³ model shows that pork production systems in the Southwest source 100% of their soybean meal originating from Midwest soybeans, whereas swine operations in the Mid-Atlantic region source only 55% of their soybean meal from the Midwest. As such, the net result was reduced overall GHG emission values for soybean meal in the Southwest states compared with those in the Mid-Atlantic region.

For DDGS, our FoodS³ model indicates that the Southwest and Mid-Atlantic regions source about 97% of DDGS from the Midwest, with only 3% of DDGS sourced within these respective regions. Although corn production in the Mid-Atlantic has the greatest GHG emission intensity for DDGS, it has less electricity grid emission intensity compared with the Southwest region which results in the Mid-Atlantic states having reduced overall emissions from DDGS compared with those in the Southwest.

The significantly greater water consumption observed for the Southwest pork production region compared with the Midwest and Mid-Atlantic regions was due to the greater proportion of corn and DDGS feed ingredients coming from arid production regions in the Southwestern states of the United States, and a greater proportion of soybean meal was estimated to be sourced from more arid areas of the Midwest (e.g., Nebraska) where larger quantities of irrigation water are used. The Mid-Atlantic region had the greatest land use attributed to corn and DDGS compared with all other regions due to the comparatively reduced yields of corn produced (7,595 kg/ha) compared with the other regions (7,846–9,729 kg/ha), and the relatively high portion of these ingredients sourced from this region.

GHG emissions from feeding program, manure, and overall

The DDGS feeding program resulted in the greatest GHG emissions from feed, manure, and overall impacts compared with all other feeding programs. This occurred because of the greater quantity of high emission-intensity feed ingredients (DDGS and soybean meal) used in diets compared with the other feeding programs, and the greater VS production rate responsible for methane production. However, the impact of feeding DDGS diets to swine on GHG emissions has been inconsistent among published studies. Trabue et al. (2022) reported that feeding a CSBM diet to finishing pigs resulted in less carbon dioxide, methane, and ammonia emissions, but greater nitrous oxide emissions per pig per day than when feeding a CSBM diet containing 28% DDGS. Mackenzie et al. (2016b) determined the environmental impacts of growing-finishing pig diets containing 26% DDGS in a multi-phase feeding program similar to the approach used in the current study, except for using carcass weight rather than live weight at the farm gate as the functional unit and reported a 16% increase in GWP compared with feeding corn-soybean meal diets.

Due to the greater GHG emission intensity of soybean meal compared with corn in all pork production regions, use of the SAA feeding program resulted in the second least GHG emissions from feed, manure, and overall compared with the other feeding programs. Compared with the CSBM feeding program, we estimated a 4.3% reduction across all regions in overall GHG emissions for the SAA feeding program. Kebreab et al. (2016) reported that supplementing diets with synthetic amino acids, with and without phytase, resulted in a 17% reduction in GHG emissions in North America, which was less than the reduction in Europe (56%) and South America (33%) compared with the unsupplemented diets. European and South American diets containing synthetic amino acids with or without phytase had a much greater impact on GWP with land use change than in North America because of the negative environmental impacts associated with using soybean meal produced in deforestation regions in South America.

As expected, the FW feeding program had the least contribution to GHG emissions from feed, manure, and overall impacts compared with the other feeding programs regardless of region. Based on the high nutritional value of the thermally processed supermarket food waste used in diets in this study, upcycling food waste into swine feed, even at a relatively low diet inclusion rate (8.6%), can substantially reduce GHG emissions by about 6% from feed and manure in U.S. pork production systems relative to feeding conventional CSBM diets due to avoidance of GHG emissions produced from landfill disposal of food waste. The use of a greater diet inclusion rate for food waste was considered to achieve a greater reduction in GHG emissions, but it was not possible due to the high crude fat content of the specific supermarket food waste source chosen for this analysis because it was a diet formulation constraint limiting greater inclusion rates. If government programs, policies, or economic incentives existed that encourage entrepreneurs to develop the collection, sorting, and processing strategies to better control the nutritional composition of sources of supermarket food waste for specific animal feeding applications, greater diet inclusion rates would be possible and more significant GHG reductions could be achieved.

Swine farms in the Midwest region had the least GHG emissions attributed to the feeding program and manure across geographic regions, regardless of the feeding program. Midwest pork production systems mainly use deep pit manure storage systems compared with the widespread use of uncovered lagoons and liquid/slurry storage systems on swine farms in the Southwest and Mid-Atlantic regions which have relatively high GHG emission intensity compared with deep pit storage.

Water consumption from feeding program, manure, and overall

Although there were small differences in water consumption per market hog produced among feeding programs within each region, the slightly less water consumption for the FW and DDGS feeding programs was a result of partial attribution of water use to ethanol in the DDGS production process, and assigning no water use to upcycling food waste into animal feed. The CSBM and PHY feeding programs had the greatest water consumption impacts because of the high corn and soybean meal usage rates among the feeding programs. In the United States, about 75% of corn and 52% of soybean production is used in domestic meat and ethanol production (NCGA, 2018). Furthermore, 80–90% of water use in the United States is attributed to agriculture, with most of the consumption in the production of crops used in animal feeds and biofuel production (Brauman et al., 2016). Matlock et al. (2011) found that about 83–93% of the water footprint in U.S. pork production systems was attributed to feeding, with only 9% attributed to drinking water, and about 75% of total water consumption was used during the growing-finishing phase of production. Furthermore, water footprints from the production of feed crops varied more than 100 times in magnitude from one region to another based on whether irrigation is used (Matlock et al., 2011). This high degree of spatial variability is why it is important to incorporate information from the subnational sourcing region for feed ingredients with the corresponding region where they are consumed by each livestock sector.

In our study, we used the FoodS³ model to estimate the potential county-level regions of feed ingredient production supplying pork production systems in the United States This approach enables a better understanding of how spatially varied impacts aggregate across pork production supply chains lead to differences in the environmental impact of feed inputs consumed in different regions. While soybeans have greater embedded water use/kg of ingredient compared with corn, the greater dietary inclusion rates for corn relative to all other feed inputs result in the greatest overall embedded water consumption across all diets coming from corn. Because water consumption was similar across feeding programs, our results indicate that feed ingredient sourcing matters more than swine diet composition when considering water impacts.

Land use emissions from feeding program, manure, and overall

The reductions in land use observed for the FW, DDGS, and SAA feeding programs compared with the CSBM and PHY programs can be largely attributed to the relative quantity of soybean meal used in diets because soybean meal has the greatest impact on land use/kg of ingredient among the major ingredients used in diets evaluated in this study. Soybean yields per hectare are much less compared with corn. However, although land use impacts for corn, soybean meal, and DDGS were less in the Midwest than Mid-Atlantic and Southwest regions, due to the comparatively greater yields from quantities sourced from the Midwest, average land use impacts were 22.8% and 18.7% greater in the Mid-Atlantic and Southwest regions, respectively, compared with the Midwest.

Thoma et al. (2016) conducted a LCA of U.S. swine production (1 kg of pig live weight at the farm gate) to quantify land use requirements and impacts associated with feeding various diets containing different feed ingredients in the three greatest production regions representing 86% of total pigs produced. In their study, feed contributed 96.7% to land occupation, 80.3% to water consumption, and 61.4% to the carbon footprint associated with pork production. In the current study, the carbon footprint associated with feed was similar to that reported by Thoma et al. (2016), with an average of 59%, but ranged from 36% to 66% depending on the feeding program and region. Thoma et al. (2016) reported that the average land occupation to produce 1 kg of pig live BW in the United States was 4.22 m²a but ranged from 4.11 m²a/kg live BW in region 7 (NE, IA, KS, MO) to 4.59 m²a/kg live BW in region 4 (KY, TN, MS, AL, GA, NC, SC, and FL). These regional differences were a result of differences in corn and soybean yields and climate, with pigs produced in regions with warmer climates having reduced feed intake which subsequently results in reduced growth rates and extended feeding periods to reach market weight. Thoma et al. (2016) also estimated that the land occupation required to produce 4 oz (113 g) of lean, boneless pork in the United States was 0.906 m²a. Although it is difficult to compare the results from Thoma et al. (2016) with our results due to different systems boundaries, it appears that our estimate for land use for the CSBM feeding program across all regions was about is 3 m²/kg live BW, which is slightly less than suggested by Thoma et al. (2016).

Pelton et al. (2021) estimated that 53% of U.S. pork production companies could reduce their GHG emissions associated with corn, soybean meal, and wheat consumption by more than 20% through the prevention of direct land use change. Results from the current study indicate that widespread implementation of DDGS, FW, and SAA grower-finisher swine feeding programs across all major U.S. pork production regions could reduce land use by 9.2%, 13.2%, and 6.5%, respectively, compared with using a traditional CSBM feeding program. If these types of diets were also fed to sows and weaned pigs to include all other stages of production, or if greater diet inclusion rates of DDGS and food waste were used, reductions in land use attributed to pork production systems could approach the 20% reduction as suggested by Pelton et al. (2021). While changing feed formulations to include ingredients requiring less land use can help alleviate land use conversion pressures, such outcomes rely in part on the assumption of maintaining a relatively stable swine population. If the U.S. pork industry were to significantly expand, there would likely be increased pressure to convert less productive land into corn and soybean production to meet increasing feed demands if commensurate increases in yields do not simultaneously occur (Beyer et al., 2022) and land use change moratoriums are not implemented.

Future considerations

While we considered the variability in environmental impacts associated with crop production and the variability in the proportion of corn, soybean meal, and DDGS sourced from various regions via supply chains, we did not consider the variability in growth performance and carcass composition responses from feeding diets in these feeding programs. Meta-analysis studies have shown that pig responses from feeding increasing dietary inclusion rates of DDGS (Jang et al., 2021), and feeding low protein diets supplemented with crystalline amino acids (Wang et al., 2018; Cappelaere et al., 2021) can vary. Furthermore, the accuracy of the estimates for N, P, and C intake, retention, and excretion derived from the NRC (2012) model used in the current study need to be validated to ensure that they reflect actual growth performance and carcass composition of pigs in U.S. production systems. Future studies should also utilize stochastic models instead of deterministic models (i.e., NRC, 2012 model) to account for the inherent variation in the nutritional quality of feed ingredients and its effects on swine growth performance as well as carcass characteristics and manure composition.

Results from our study indicate that changing swine diet composition from conventional corn and soybean meal diets to alternative diets can change GHG, water consumption, and land use by +5.4% to −6%, +1.1% to −12.9%, and +1.0% to −14.9% depending on the type of diet and corresponding feeding program chosen. Future studies are needed to determine the additional environmental benefits and profitability that can be achieved by using precision feeding programs where a specific amount of the “right feed is provided to the right pigs at the right time” (Andretta et al., 2018; Pomar and Remus, 2019; Pomar et al., 2021). Studies have shown that the use of precision feeding approaches in conventional pork production systems can reduce the cost of production by more than 8%, protein and phosphorus intake (25%) and excretion (40%), and GHG emission by 6% through improved nutrient utilization efficiency (Pomar and Remus, 2019). Further consideration of the tradeoffs between these environmental impacts is critical. Even within our study, none of the feeding programs evaluated was the “best” across N and P utilization efficiency, GHG emissions, water consumption, and land use, with results being more disparate when considering the best two feeding programs within each environmental impact category. For example, the DDGS diet had the second least N, P, water consumption, and land use impacts, but the greatest GHG impacts. More work is needed to assist farmers and downstream companies in deciding among these tradeoffs.

Our analysis focused on conventional intensive pork production systems which dominate the U.S. pork industry. However, future studies are needed to compare the potential advantages and disadvantages of conventional systems with organic, natural, and other alternative pork production systems to evaluate profitability and tradeoffs for meeting environmental, animal welfare, and pork quality goals similar to studies that have been conducted for contrasting pork production systems in Europe (Dourmad et al., 2014).

Swine farms in the United States have historically been located where abundant and low-cost feed resources (corn and soybean) and slaughter facilities exist. More recently, states where modern swine confinement facilities could be constructed and located long distances from other farms (e.g., Oklahoma, Texas, Utah) became major pork production regions because of greater biosecurity to reduce the risk of disease transmission necessary for maintaining high health status to optimize productivity. Future research should consider whether this biosecurity advantage outweighs the environmental footprint of transporting feed resources the additional distances to those locations (which may be marginal), and the potential increase in emissions from transitioning corn and soybean production to marginal lands nearer to these distant pork production locations. Growing feed crops in more marginal areas would increase the GHG, water, and land impacts resulting from requiring more fertilizer, irrigation, and reduced yields.

Climate change will also cause the need to adapt and shift optimal cultivation geographies northward in the United States for corn, soybeans, and other major crops (Burchfield, 2022), which will have multiple impacts on the environmental footprint of feed ingredients used in livestock production systems. Some of these effects have been characterized including mycotoxin contamination (Yu et al., 2022), which reduces nutrient utilization efficiency and productivity, and decreased soybean yields (Landau et al., 2022), which will increase the GHG emissions, water consumption, and land use footprints in most regions beyond current levels.

However, deglobalization and disruptions in global feed ingredient supply chains could become an advantage for U.S. pork production and environmental footprint of exported pork if multiobjective feed formulation were to be used to include LCA impacts of feed ingredients as formulation constraints and if precision feeding practices become more widely implemented. A recent study conducted in France (de Quelen et al., 2021) showed that the use of multi-objective feed formulation in precision swine growing-finishing feeding programs using local feed ingredients or reduced environmental impact diets resulted in the same growth performance and carcass composition compared with conventional diets including imported soybean meal.

Crop and livestock production systems are the greatest contributors to undesirable global N and P nutrient flows (Bouwman et al., 2013), and the amounts and forms of N, P, and GHG emissions associated with crop production and conventional swine confinement operations in the United States have changed significantly in recent years (Glibert, 2020). Solutions for improving N and P utilization efficiency must include feed production, animal production, and manure management (Liu et al., 2017; Metson et al., 2020). Although a few studies have been conducted to evaluate N (Dattamudi et al., 2020; Correndo et al., 2022) and P (Margenot et al., 2019) flows for U.S. corn and soybean production, they have not been spatially linked to acidification and eutrophication potential associated with N and P utilization efficiency of various swine feeding programs like those evaluated in the current study. However, the emergence of spatialized data that estimates global warming potential, eutrophication, and acidification impacts in U.S. crop (soybean) production (Romeiko et al., 2020) could be applied to assess N, P, and C flows of ingredients used in swine diet types in each U.S. region in future studies as more of these data are generated for other common feed ingredients.

In conclusion, GHG emissions, water consumption, and land use footprints of corn, soybean meal, and DDGS vary substantially among U.S. regions, which subsequently result in major differences in environmental impacts from feeding programs and manure between major pork production regions in the United States Using spatially explicit, county-scale LCA data for sourcing corn, soybean meal, and DDGS, along with multi-objective feed formulation to include LCA data of feed ingredients, can substantially reduce the environmental footprint of U.S. pork production. However, pork production systems outside of the Midwest region, which have the greatest feed, manure, and pork production environmental footprint, have a distinct disadvantage in reaching the same environmental sustainability goals if they cannot source and use large quantities of corn, soybean meal, and DDGS from the Midwest. As a result, there are greater incentives for pork production systems in the Mid-Atlantic and Southwest regions to use alternative feed ingredients with less environmental impact such as thermally processed supermarket food waste, bakery by-products, and rendered animal by-products in swine diets. In the long-term, pork production systems should explore potential partnerships and contractual arrangements with corn and soybean farmers that use more sustainable crop production practices (e.g., cover crops, no-till, no irrigation) to reduce the environmental footprint of corn, soybean meal, and DDGS use in swine feeding programs. In addition, the widespread adoption of precision feeding technologies is essential for improving nitrogen, phosphorus, and carbon utilization in pork production, and further evaluation of the tradeoffs between the environmental impacts of feed ingredients and feeding programs needs to be addressed. Finally, renovating manure collection, storage, and application practices in pork production systems in the Mid-Atlantic and Southwest regions to include anaerobic digesters for biogas production and use of greater amounts of renewable energy are needed to further improve the environmental sustainability of U.S. pork production.

Glossary

Abbreviations

AP: acidification potential
BW: body weight
C: carbon
CO₂ equiv.: carbon dioxide equivalent
CP: crude protein
CSBM: corn-soybean meal
DDGS: dried distillers grains with solubles
DE: digestible energy
DM: dry matter
EP: eutrophication potential
EPA: Environmental Protection Agency
FTU: phytase units
FW: food waste
GE: gross energy
GFLI: Global Feed LCA Institute
GHG: greenhouse gases
GWP: global warming potential
LCA: Life Cycle Assessment
ME: metabolizable energy
MJ: megajoules
N: nitrogen
N₂O: nitrous oxide
P: phosphorus
PHY: phytase
SAA: synthetic amino acids
SID: standardized ileal digestibility
STTD: standardized total tract digestible
UE: urinary energy
U.S.: United States
VS: volatile solids

Contributor Information

Gerald C Shurson, Department of Animal Science, University of Minnesota, St. Paul, MN 55108, USA.

Rylie E O Pelton, Institute on the Environment, University of Minnesota, St. Paul, MN 55108, USA.

Zhaohui Yang, Department of Animal Science, University of Minnesota, St. Paul, MN 55108, USA.

Pedro E Urriola, Department of Animal Science, University of Minnesota, St. Paul, MN 55108, USA.

Jennifer Schmitt, Institute on the Environment, University of Minnesota, St. Paul, MN 55108, USA.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Conflict of Interest Statement

The authors declare no competing interests.

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PERMALINK

Environmental impacts of eco-nutrition swine feeding programs in spatially explicit geographic regions of the United States

Gerald C Shurson

Rylie E O Pelton

Zhaohui Yang

Pedro E Urriola

Jennifer Schmitt

Abstract

Introduction

Material and Methods

Diet formulations and feeding programs

Table 1.

Table 2.

Table 3.

Estimation of nitrogen, and phosphorus excretion, and manure volatile solids production

Spatially explicit regions

Figure 1.

Environmental impacts of dietary ingredients

Environmental impacts of manure management

Avoided impacts

Results

Feed formulation

Estimated nitrogen and phosphorus intake, retention, and excretion

Table 4.

Estimated volatile solids excretion

Table 5.

Environmental impact factors for feed ingredients among regions

Table 6.

Table 7.

Effect of feeding program and region on GHG emissions

Table 8.

Effect of feeding program and region on water consumption

Table 9.

Effect of feeding program and region on land use

Table 10.

Discussion

General overview

Nitrogen, phosphorus, and carbon balance

Nitrogen utilization efficiency

Phosphorus utilization efficiency

Carbon utilization efficiency

Environmental impact factors for feed ingredients among regions

GHG emissions from feeding program, manure, and overall

Water consumption from feeding program, manure, and overall

Land use emissions from feeding program, manure, and overall

Future considerations

Glossary

Abbreviations

Contributor Information

Funding

Conflict of Interest Statement

Literature Cited

ACTIONS

PERMALINK

RESOURCES

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