Energy use and nutrient cycling in pig production systems

Final Report for GNC07-078

Project Type: Graduate Student
Funds awarded in 2007: $9,969.00
Projected End Date: 12/31/2009
Grant Recipient: Iowa State University
Region: North Central
State: Iowa
Graduate Student:
Faculty Advisor:
Mark Honeyman
Iowa State University
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Project Information

Summary:

This project quantified the energy use in the construction and operation of different types of pig production systems in Iowa. In general producing pigs in Iowa in 2009 requires nearly 85% less non-renewable energy compared to 1975. Using bedded hoop barns for gestating sows and grow finish pigs requires less energy to heat and ventilate buildings but more energy to grow and process feed than conventional systems. The total energy used for both housing systems is very similar. Energy use for pig production is influenced by crop sequence and diet strategy with nitrogen management being the major leverage point.

Introduction:

United States pig production is concentrated in the North Central Region, and is a major influence on the economic and ecological well-being of that community. Although often viewed as isolated entities at a macro-level, production of both crops and livestock are heavily influenced by each other. Recognizing influences between crops and livestock, and particularly utilizing complementary aspects of pig production and cropping systems is essential for achievement of greater sustainability within the North Central United States.

Energy is used in all aspects of pig production, from the manufacture of materials used in building construction to the cultivation and processing of feedstuffs. Historically the availability of fossil fuels has minimized pressure to critically consider all uses of energy in pig production. Interest in non-solar energy use for all sectors of society is increasing due to rising energy prices, uncertainty about access to fossil fuel reserves, and growing consensus about the deleterious implications fossil fuel use has for global climate. Comprehensive, accurate information is critical to informed decision making. However analysis of energy use by modern pig farms in Iowa, the region, and United States is lacking.

Life cycle assessment (LCA) is a technique used to quantify and compare environmental impacts of products or processes. Although most commonly applied to manufacturing processes, LCA is increasingly being applied to agriculture. Previous LCA’s of swine production have focused on European systems, particularly Denmark (Halberg, 1999; Zhu and van Ierland, 2004; Basset-Mens and van der Werf, 2005; Ericksson et al., 2005; Williams et al., 2006; Dalgaard et al., 2007; Meul et al., 2007). There are fundamental differences between European and United States swine production that limits the application of European results to inform decision making by pig producers in the United States. European swine diets typically include more variety of feed ingredients and often include high amounts of small grains such as barley. Peas, rapeseed cake, and soybean meal are all commonly used as protein sources in European swine diets. In the United States, swine diets are almost entirely comprised of corn and soybean meal. Growing pigs are usually limit fed in Europe but fed ad libitum in the United States. Feeding pelleted or liquid feeds is Europe is common while in the United States almost all diets are ground and fed dry. Some US farms provide water at the feeder, encouraging consumption of a wet-dry feed, but this strategy is very different from liquid feeding systems seen in Europe. Finally climate conditions and primary environmental concerns differ between Europe and the United States.

Broadly, a pig production system consists of three features: the buildings used to house pigs, the diets fed the animals, and the cropland used to produce the feedstuffs. The purpose of this project is to examine non-solar energy use of different facility type × crop sequence × diet formulation strategies. Greenhouse gas emissions are also estimated based on non-solar energy use.

Conventional farrow-to-finish swine facilities in Iowa are mechanically ventilated buildings with liquid manure handling systems. Pigs are born in farrowing crates and at weaning are moved to a heated nursery facility. As pigs grow, they are moved from nursery facilities to larger grow-finish buildings. Grow-finish buildings typically house 1,200 animals in pens of 30-60 animals. The entire floor space is slatted concrete. Gestation occurs in buildings similar to grow-finish buildings except pens are replaced with individual gestation stalls. Conventional housing for swine in Iowa and a hoop barn-based alternative have been detailed and examined (Lammers et al., 2009b; Lammers et al., 2009c). The hoop barn-based alternative uses similar farrowing and nursery facilities as the conventional system, but grow-finish pigs and gestating sows are housed in bedded hoop barns. Hoop barns in Iowa are 21.9 × 9.1 m QuonsetTM- shaped structures that have been previously described (Honeyman et al., 2001; Brumm et al., 2004; Harmon et al., 2004). Hoop barn sidewalls are approximately 1.5 m high and consist of wooden posts and sidewalls. Tubular steel arches are attached to the posts, forming a hooped roof. An ultraviolet light resistant, high-density polyethelyne tarp is pulled over the arches and fastened to the sidewalls. The floor is solid, usually concrete, with raised areas for eating and drinking. The rest of the floor is bedded with corn stalks or other plant materials. Buildings for grow-finish pigs are managed as a single pen with 180–200 animals per pen (Honeyman et al., 2001; Honeyman and Harmon, 2003). Gestating sows in hoop barns are managed in group pens with individual feeding stalls (Lammers et al., 2007; Lammers et al., 2008a).

The most common crop sequence in Iowa is a corn-soybean rotation. This sequence is highly productive in terms of starch and amino acids produced, but is heavily reliant on fossil fuels to provide fertility and has been associated with a number of undesirable ecological impacts. For this analysis, an alternative of corn-soybean-corn-oat under-seeded with a leguminous cover crop was examined.

Two diet formulation strategies are also considered. The first formulation strategy (SIMPLE) does not include synthetic amino acids or phytase. The second (COMPLEX) reduces crude protein content of the diet by using L-lysine to meet SID lysine requirements of pigs and includes the exogenous enzyme phytase. Use of synthetic amino acids and exogenous phytase is common practice in modern pig production based on economics and environmental regulation. The industrial processes for manufacturing L-lysine and exogenous phytase is energy intensive. The two formulation strategies were selected in order to evaluate the systemic effectiveness of substituting synthetic amino acids and exogenous enzymes for more basic feed ingredients in terms of non-solar energy use.

This project summarizes the non-solar energy use of pig production systems in Iowa. The baseline system—pigs housed in conventional confinement facilities and fed complex corn-soybean meal diets produced on land cultivated in a corn-soybean sequence—is representative of how the majority of pigs in the Midwest United States are produced. Selected combinations of facility type × crop sequence × diet formulation strategies were compared to the baseline system. Greenhouse gas emissions are also estimated based on non-solar energy use. This project provides a current analysis of modern pig production systems and identifies leverage points for minimizing non-solar energy use and associated greenhouse gas emissions by pig production systems.

Project Objectives:

Three expected outcomes were identified in the proposal of this research project for the short, intermediate, and long term. They are as follows:
1. Short term: quantification of energy use in pig production systems.
2. Intermediate term: objectively evaluate energy use choices and alternatives in pig production systems.
3. Long term: practice and policy enhancing the sustainability of the region and nation.

Research

Materials and methods:

Process analysis methodology was used to calculate direct and indirect energy inputs into and through pig production systems based on physical material flows (Jones, 1989). Similar to previous assessments (Meul et al., 2007) a cradle-to-gate approach of LCA that included embodied energy one step before the farm was used. Consistent with process analysis methods, we did not include solar energy and human labor inputs (Jones, 1989). Managing pigs in hoop barns requires a different set of skills and proficiencies compared to managing pigs in conventional systems but labor is generally assumed to be similar for both types of housing systems.

Resources such as energy and carbon are categorized as embodied or operating based on how they are used. Embodied energy refers to the quantity of energy required to manufacture, provide, or supply a product, material, or service (Hammond and Jones, 2008b). In pig production, energy used to produce facility components such as concrete, steel, plastics, and lumber are examples of embodied energy. Operating energy is the energy required for a system to function on a daily basis—electricity for ventilation systems and energy in feed consumed by pigs for example. Embodied carbon is the amount of greenhouse gases released during the production of a product (Hammond and Jones, 2008b) and represents the initial global climate change associated with a product. Emissions of compounds associated with global climate change are often expressed in terms of carbon dioxide equivalents. The operating carbon is simply the carbon dioxide equivalents released through consumption of operating energy inputs associated with pig production.

Three non-solar energy sources were considered: diesel fuel, liquefied petroleum gas, and electricity. Consumption of each fuel source results in emission of different amounts of greenhouse gases (IPCC, 2006, 2007; EPA, 2008). Global warming potential (GWP) is a measure of how much a given mass of greenhouse gas contributes to global climate change over a set period of time. Reporting greenhouse gas emissions in terms of 100-yr GWP relative to carbon dioxide is standard international practice (IPCC, 2006, 2007).

Simplified design models of buildings used for each stage of pig production were generated and used to estimate building material use (Lammers et al., 2009c). The amount of pig spaces needed for a given level of production was first determined based on industry surveys and databases (USDA, 2007; PigCHAMP, 2008). Modeled building dimensions, layout, and material choices were determined based on interviews with construction firms, facility managers, and industry consultants. Five primary building materials were estimated: concrete, steel, lumber, insulation, and thermoplastics. The mass of each type of building materials used was then multiplied with reference values for construction materials (Hammond and Jones, 2008a) to calculate the embodied energy and carbon of materials present in a newly constructed pig facility complex. Energy use for site preparation was estimated based on construction estimating references (RES, 1990; Mossman and Plotner, 2006).

Energy use for one 365-day period was modeled for each phase of pig production (Lammers et al., 2009b). The analysis includes energy used for thermal environment control (heating and ventilation), pumping water, cleaning facilities, and providing illumination, as well as feed consumption and bedding use as appropriate. Historic hourly temperature data for North Central Iowa (Kjelgaard, 2001) was combined with pig flow assumptions to model energy use for heating and ventilating each type of pig facility.

Different crop production scenarios, processes for preparing diet ingredients, and efficacy of various formulation strategies to minimize non-solar energy use and 100-yr global warming potential (GWP) from emissions associated with production of swine feed were detailed and examined (Lammers, 2009;Lammers et al. 2009d). A crop production model for Iowa was developed and used to evaluate three types of non-solar energy inputs: diesel fuel, liquefied petroleum gas, and electricity. The energy used to produce key crop-production inputs that would be produced only if crop production occurred—seed, fertilizers, and pesticides for example—were also estimated (Lammers, 2009). The non-solar energy use and resulting 100-yr GWP associated with producing and delivering 13 swine feed ingredients in Iowa was calculated and summarized. Phase-specific swine diets were formulated to omit or include synthetic amino acids and endogenous phytase (SIMPLE or COMPLEX respectively). For each general formulation scheme (SIMPLE or COMPLEX) various ingredient choices were considered based upon crop production scenarios.

A final summary analysis was performed that considered different combinations of facility type, crop sequence, and diet formulation strategy (Lammers et al., 2009e). This analysis considered nutrient excretion from pigs based on diet formulation. It also considered nutrient delivery to cropland by various forms of pig manure (liquid slurry from conventional confinement or composted solid from hoop barns) and displaced synthetic fertilizers. The total non-solar energy use and 100-yr GWP associated with main components of the entire pig production system were summarized for selected scenarios and reported.

Research results and discussion:

Construction Resource Consumption

Pig production systems using hoop barns for gestating sows and grow-finish require fewer physical construction resources and investment capital than conventional facilities (Lammers et al., 2009c). More total land is needed to build a hoop barn-based swine production system, however land accounts for less than 5% of the total capital investment in newly constructed swine systems. Labor is the single largest expense when building pig facilities. Increasing the scale of production from 5,200 pigs/year to 15,600 pigs/year reduces construction resource use and capital investment per pig sold more dramatically in the conventional system than in one using hoop barns for gestating sows and finishing pigs. In terms of construction resource use and costs, hoop barns for swine are a lower cost alternative that is less scale dependant than conventional confinement facilities (Lammers et al., 2009c).

Conventional pig production facilities required 15-50% more physical materials to construct than a similarly sized hoop barn-based system. Because hoop barns require thermoplastic tarps the hoop barn-based system represents an embodied energy savings of only 16% compared to conventional facilities. Our analysis assumes each hoop barn will use 2 thermoplastic tarps over the course of a 15-yr useful life span. The hoop barn-based system requires 18% less embodied carbon dioxide compared to conventional facilities (Lammers et al., 2009b).

Operating Energy and Carbon of Pig Production Facilities

Operating energy is the energy required for a facility to function on a daily basis and operating carbon refers to the greenhouse gases released by consumption of operating energy. The energy value of feed fed to pigs dwarfs all other operating energy inputs into a pig production system. However the nonrenewable energy used to operate pig facilities is not negligible. Because feed crops are grown annually their consumption results in no net greenhouse gas emissions per se. (Cultivation and processing of feed does result in release of greenhouse gas emissions. This release is accounted for in the next segment of the analysis.) Thus nonrenewable energy sources account for 100% of the greenhouse gas emissions resulting from daily operation of pig production facilities. We estimate that for every pig produced in the conventional system 185.4 MJ of nonrenewable energy is invested in simply operating the facilities where the pigs are housed. This fuel consumption results in emission of 22.68 kg of carbon dioxide per pig sold. Alternatively the system that uses hoop barns for gestation and grow-finish requires 113.9 MJ of nonrenewable energy for facility operation and emits 9.86 kg of carbon dioxide per pig sold (Lammers et al., 2009b).

The grow-finish phase of production accounts for 75% of total feed consumption associated with producing 1 market pig. Non-renewable energy use by the grow-finish phase accounts for less than 50% of the total non-renewable energy use associated with producing 1 market pig. Thus life cycle assessments that focus exclusively on the grow-finish phase of production ignore more than 50% of total non-renewable energy used to operate pig facilities. Thorough life cycle assessments of pig production must include operating the gestation, farrowing, and nursery facilities necessary to produce grow-finish pigs.

Swine Feedstuffs and Feeding Strategies

The non-solar energy required to grow, process, or manufacture 13 common feedstuffs for swine in Iowa was summarized (Lammers et al., 2009d). This is an update of an earlier review {LaHore, 1978 #272} and is the first United States based assessment. It is expected that this summary will be expanded and refined by others. Including the exogenous enzyme phytase in pig diets allows the reduction of mineral phosphorus sources and is energetically favorable. Simply adding phytase allows removal of nearly all mineral sources of phosphorus and reduces energy required to produce pig diets by 4-6%. Feeding synthetic lysine enable meeting the amino acid needs of pigs with less soybean meal and results in a non-renewable energy savings of less than 1% per kg of pig feed produced. Because feeding phytase and synthetic amino acids also potentially reduce the excretion of phosphorus and nitrogen by pigs, incorporating these ingredients in pig diets is doubly beneficial.

Diets that incorporated full-fat soybeans were found to require more non-renewable energy for diet production than ones that used soybean meal. Processing soybeans into soybean oil and soybean meal is an energy intensive step, however the benefits outweigh the costs in terms of nonrenewable energy and 100-yr GHG emissions. Other European analyses have reported that replacing soybean meal with other sources of amino acids is energetically favorable (Ericksson et al., 2005). However those analyses assume that soybean meal is imported from South America while alternatives are grown locally. In Iowa, and most of the Midwest United States soybeans are extensively processed near the location of pig production. The previously reported advantages of displacing soybean meal with alternative protein sources (Ericksson et al., 2005) may not apply directly to Iowa or the Midwest United States.

Biofuel production is growing rapidly in the Midwest United States and our analysis considers ethanol production from corn grain and biodiesel production from soybean oil. The co-products of biofuel production—dried distillers grains with solubles and crude glycerol respectively—have been shown to be suitable feedstuffs for pigs (Shurson et al., 2004; Lammers et al., 2008b; Lammers et al., 2009a). Incorporating these feedstuffs into pig diets is not energetically favorable in terms of Net Energy for pig production (NE) returned for non-solar energy input. However if the decision has already been made to produce biofuels feeding these co-products may be economical for individual swine producers.

Although there are likely many benefits of increasing the complexity of crop sequence beyond a conventional corn-soybean rotation, NE per unit of non-solar energy input is not one of them. In our analysis the corn-soybean crop sequence required more non-solar energy per square meter than alternatives, but also produced more starch, and NE per unit of input energy (Lammers, 2009). In terms of effectively converting non-solar energy resources into pig diets, a diet of primarily corn and soybean meal produced from a corn-soybean rotation is optimal under current conditions. As crop production strategies and feed processing techniques evolve, this may change, however at this point in time, typical corn-soybean meal diets that contain synthetic amino acids and exogenous phytase appear to be the best choice in terms of non-solar energy use per unit of pig growth.

Optimizing Non-solar Energy Use in Pig Production Systems

In Iowa, one market pig housed in conventional confinement facilities and fed a complex diet of corn and soybean meal with synthetic amino acids and exogenous phytase requires 744 MJ of non-solar energy. This level of non-solar energy use results in emission of greenhouse gases equivalent to 64.9 kg carbon dioxide. Of the non-solar energy consumed, facility construction and operation require 87.0 and 200.5 MJ/pig while cultivation of crops and processing of feed requires 354.1 and 102.4 MJ/pig sold respectively.

Alternatively, raising one market pig in Iowa using hoop barns for gestating sows and grow finish pigs requires 767.9 MJ of non-solar energy and results in the 100-yr GWP of 58.2 kg carbon dioxide. In the hoop barn-based system, facility construction and operation require 73.2 and 124.9 MJ/pig while cultivation of crops and processing of feed requires 464.3 and 105.5 MJ/pig. The hoop barn-based system requires less non-solar energy for construction and operating the barns themselves. However it is assumed that more feed is fed to growing pigs and gestating sows housed in hoop barns as compared to conventional facilities, thus the hoop barn-based system requires more energy for feed production and in turn 3% more total non-solar energy per pig sold.

It should be noted that the total non-solar energy use for pig production is very similar for the two housing options examined. There is a numeric difference of approximately 24 MJ/market pig between the two systems. This is equivalent to the amount of energy found in about 2 pounds of butter. Despite using more total non-solar energy per pig marketed the hoop barn-based system results in 10% less 100-yr GWP due to the differences in fuel mixes between the two systems. Conventional pig production systems rely more extensively on electricity than alternatives that incorporate hoop barns. Systems using hoop barns rely more heavily on non-solar energy used for producing pig feed because of assumed feed consumption differences between conventional systems and hoop barn-based alternatives.

In both systems producing pig feed is the largest user of non-solar energy. Delivering nitrogen to crops accounts for nearly 50% of the non-solar energy use associated with crop production for pig feed. Thus nitrogen management is essential to management of non-solar energy use by pig production systems. Our analysis includes return of manure slurry and composted bedding pack from pig production facilities. Based on our analysis the handling of excreted nutrients is critical to nitrogen retention and optimization of non-solar energy use in pig production systems.

Current reports from Europe of non-solar energy use for pig production range from 5.3–23.5 MJ/kg live weight (Basset-Mens and van der Werf, 2005; Ericksson et al., 2005; Williams et al., 2006). European reports assumed very different crop production and feed processing scenarios than we examined. Others have not included facility operation or construction and focused exclusively on feeding strategies. With more than 35% of the total non-solar energy use required to produce pigs associated with facility construction and operation examinations which exclude these factors are incomplete. We estimate the raising pigs in conventional confinement systems operating in Iowa use 5.5 MJ non-solar energy per kg of live weight pig. The alternative system using hoop barns for grow-finish and gestating sows may require slightly more non-solar energy or 5.6 MJ/kg of live weight.

There are three major differences between the conventional and hoop barn-based systems. The first is the non-solar energy necessary to operate the buildings on a daily basis. The second is the amount of feed required by pigs housed in the different facility types. The final is the amount of nitrogen retained in manure and ultimately delivered to cropland in the two systems. The hoop barn-based system has a clear advantage in terms of energy used for building operation. Research has reported raising pigs in hoop barns require approximately 3% more feed than conventional facilities (Honeyman and Harmon, 2003; Lammers et al., 2007; Lammers et al., 2008a). It should be noted that the genetic lines used in those studies have been developed for optimal performance in the conventional confinement facility. The fact that performance between the two housing systems was similar points to the adaptability of the pig. It is possible that through genetic selection and refinement of husbandry practice the feed consumption by pigs housed in bedded hoop barns may be equal to or less than feed consumption in conventional systems.

Our analysis assumes that more nitrogen is lost from the bedding pack in a hoop barn than from the deep-pit of a conventional swine facility. However there are multiple strategies that might reduce nitrogen loss from bedding packs that remain to be explored. Hoop barns for pigs are a relatively new technology that offer options for producers. Although the conventional system did not develop within a vacuum, as we strive to optimally allocate non-solar energy reserves and reduce the global warming potential of pig production, support for alternative systems such as hoop barns is warranted, particularly in the area of bedding pack management.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

To date this work has resulted in one doctoral dissertation, one peer-reviewed publication, and three manuscripts in various stages of the review process. Those publications are as follows:

Lammers, P. J. 2009. Energy and nutrient cycling in swine production systems. PhD Diss, Iowa State Univ., Ames.

Lammers, P. J., M. S. Honeyman, J. D. Harmon, J. B. Kliebenstein, and M. J. Helmers. 2009. Construction resource use of two different types and scales of Iowa swine production facilities. Applied Engineering in Agriculture 25: 585–593.

On-going Manuscripts

Lammers, P. J., M. S. Honeyman, J. D. Harmon, J. B. Kliebenstein, and M. J. Helmers. 2009 Energy and carbon inventory of swine production facilities. Submitted to Agricultural Systems.

Lammers, P. J., M. D. Kenealy, J. B. Kliebenstein, J. D. Harmon, M. J. Helmers, and M. S. Honeyman. 2009. Non-solar energy use and 100-yr global warming potential of Iowa swine feedstuffs and feeding strategies. Submitted to Journal of Animal Science.

Lammers, P. J., M. D. Kenealy, J. B. Kliebenstein, J. D. Harmon, M. J. Helmers, and M. S. Honeyman. 2009. Optimizing use of non-solar resources in pig production: An examination of Iowa systems. In preparation.

Additionally portions of this work have been presented to groups of producers through Iowa State University Extension programs as well as meetings of Practical Farmers of Iowa and the Land Stewardship Project of Minnesota. Portions of this work have been presented to scientific audiences at regional and national meetings. This work has also contributed to two other on-going life cycle assessments of pork production in the United States.

Project Outcomes

Project outcomes:

This project quantified the energy use in the construction and operation of different types of modern pig production systems in Iowa. The last time this was assessed was 1975 (Reid et al., 1980). In general producing pigs in Iowa in 2009 requires nearly 85% less non-renewable energy compared to 1975. The impact of this analysis is yet to be realized but provides essential background material for further examination of specific strategies aimed at reducing non-solar energy use and 100-yr GWP of pig production systems.

Recommendations:

Areas needing additional study

The results of this project highlight three areas of future research: reducing losses of excreted nitrogen during storage and application of pig manure and compost; management of thermal environment in pig facilities; and genetic selection for feed efficiency in bedded systems.

Nitrogen management is the key to effective use of non-solar energy resources in pig feed production. Strategies for reducing nitrogen loss from pig excrement is an area of on-going research and rightly so. In addition to the conventional systems most commonly considered methods for reducing nitrogen loss from bedding packs in alternative pig production systems remains to be explored.

Most non-solar energy not attributed to production of feed is used to heat and ventilate pig barns. Adequate ventilation is required for pig and worker health. Also heating of pig barns during winter months is likely essential for maintaining optimal growth rates, especially in young pigs. However an analysis of approaches to maintaining thermal environment that considers not only maximal pig growth but also total non-solar energy use and 100-yr GWP remains to be explored. Identifying alternative heating and cooling technologies and strategies may result in significant reductions in non-solar energy use in pig production systems.

Finally the genetic selection of types of pigs that perform optimally in alternative pig production systems such as hoop barns should not be overlooked. So far the genetic lines used in most if not all examinations of alternative housing systems have been developed for optimal performance in conventional confinement systems. Although most pigs in the United States are reared in conventional confinement facilities, the potential for developing genetic lines ideal for alternative production systems remains great.

Literature Cited

Basset-Mens, C., and H. M. G. van der Werf. 2005. Scenario-based environmental assessment of farming systems: The case of pig production in France. Agriculture, Ecosystems and Environment 105: 127–144.

Brumm, M. C., J. D. Harmon, M. S. Honeyman, J. B. Kliebenstein, S. M. Lonergan, R. Morrison, and T. Richard. 2004. Hoop barns for grow-finish swine. AED 44. MidWest Plan Service, Ames, IA.

Dalgaard, R., N. Halberg, and J. E. Hermansen. 2007. Danish pork production: An environmental assessment. DJF Animal Science 82: 1–34.

EPA. 2008. eGRID subregion GHG output emission rates for year 2005. Washington, D. C. Available online: http://www.epa.gov/cleanenergy/energy-resources/egrid/index.html. Accessed: May 28, 2009.

Ericksson, I. S., H. Elmquist, S. Stern, and T. Nybrant. 2005. Environmental systems analysis of pig production: The impact of feed choice. International Journal of Life Cycle Assessment 10: 143-154.

Halberg, N. 1999. Indicators of resource use and environmental impact for use in a decision aid for Danish livestock farms. Agriculture, Ecosystems and Environment 76: 17–30.

Hammond, G., and C. Jones. 2008a. Inventory of carbon and energy. Version 1.6a. Department of Mechanical Engineering, University of Bath, Bath, UK. Available online: www.bath.ac.uk/mech-eng/sert/embodied/. Accessed: May 28, 2009.

Hammond, G. P., and C. I. Jones. 2008b. Embodied energy and carbon in construction materials. Proceedings of the Institution of Civil Engineers: Energy 161: 87–98.

Harmon, J. D., M. S. Honeyman, J. B. Kliebenstein, T. Richard, and J. M. Zulovich. 2004. Hoop barns for gestating swine. AED 44. MidWest Plan Service, Ames, IA.

Honeyman, M. S., and J. D. Harmon. 2003. Performance of finishing pigs in hoop structures and confinement during summer and winter. Journal of Animal Science 81: 1663-1670.

Honeyman, M. S., J. D. Harmon, J. B. Kliebenstein, and T. L. Richard. 2001. Feasibility of hoop structures for market swine in Iowa: Pig performance, pig environment, and budget analysis. Applied Engineering in Agriculture 17: 869–874.

IPCC. 2006. 2006 ipcc guidelines for national greenhouse gas inventories. Kamiyamaguchi, Japan. Available online: http://www.ipcc-nggip.iges.or.jp/public/2006gl/index.html. Accessed: May 28, 2009.

IPCC. 2007. Climate change 2007: The physical science basis. Intergovernmental Panel on Climate Change, Geneva, Switzerland.

Jones, M. R. 1989. Analysis of the use of energy in agriculture—approaches and problems. Agricultural Systems 29: 339–355.

Kjelgaard, M. J. 2001. Engineering weather data. McGraw-Hill, New York, NY.

LaHore, R., and B. Croke. 1978. Energetics of stockfeed production. Animal Feed Science and Technology 3: 1–14.

Lammers, P. J. 2009. Energy and nutrient cycling in swine production systems. PhD Diss, Iowa State Univ., Ames.

Lammers, P. J., D. M. S. Honeyman, and B. J. Kerr. 2009a. Biofuel co-products in swine diets: Combining DDGS and glycerol. Journal of Animal Science Abstract #167 Midwest ASAS meeting.

Lammers, P. J., M. S. Honeyman, J. D. Harmon, and M. J. Helmers. 2009b. Energy and carbon inventory of Iowa swine production facilities. Agricultural Systems under review.

Lammers, P. J., M. S. Honeyman, J. D. Harmon, J. B. Kliebenstein, and M. J. Helmers. 2009c. Construction resource use of two different types and scales of Iowa swine production facilities. Applied Engineering in Agriculture 25: 585–593.

Lammers, P. J., M. S. Honeyman, J. B. Kliebenstein, and J. D. Harmon. 2008a. Impact of gestation housing system on weaned pig production cost. Applied Engineering in Agriculture 24: 245-249.

Lammers, P. J., M. S. Honeyman, J. W. Mabry, and J. D. Harmon. 2007. Performance of gestating sows in bedded hoop barns and confinement stalls. Journal of Animal Science 85: 1311-1317.

Lammers, P. J., M. D. Kenealy, J. B. Kliebenstein, J. D. Harmon, M. J. Helmers, and M. S. Honeyman. 2009d. Non-solar energy use and 100-yr global warming potential of Iowa swine feedstuffs and feeding strategies. Journal of Animal Science under review.

Lammers, P. J., M. D. Kenealy, J. B. Kliebenstein, J. D. Harmon, M. J. Helmers, and M. S. Honeyman. 2009e. Optimizing use of non-solar resources in pig production: An examination of Iowa systems. in preparation.

Lammers, P. J., B. J. Kerr, T. E. Weber, K. Bregendahl, S. M. Lonergan, K. J. Prusa, D. U. Ahn, W. C. Stoffregen, W. A. Dozier III, and M. S. Honeyman. 2008b. Growth performance, carcass characteristics, meat quality, and tissue histology of growing pigs fed crude glycerin-supplemented diets. Journal of Animal Science 82: 2962–2970.

Meul, M., F. Nevens, D. Reheul, and G. Hofman. 2007. Energy use efficiency in specialised dairy, arable, and pig farms in Flanders. Agriculture, Ecosystems and Environment 119: 135–144.

Mossman, M. J., and S. C. Plotner (eds). 2006. RSMeans facility construction cost data. 22nd edition. RSMeans Construction Publishers and Consultants, Kingston, MA.

PigCHAMP. 2008. Benchmarking summaries: 2004 and 2006. Pig CHAMP, Ames. Available online: http://www.pigchamp.com/benchmarking.asp. Accessed: March 6, 2008.

Reid, J. T., P. A. Oltenacu, M. S. Allen, and O. D. White. 1980. Cultural energy, land and labor requirements of swine production systems in the U.S. In: D. Pimentel (ed.) CRC handbook of energy utilization in agriculture. p 393–403. CRC Press Inc., Boca Raton, FL.

RES. 1990. Process plant construction estimating standards. Richardson Engineering Systems Inc., Mesa, AZ.

Shurson, G., M. Speihs, and M. Whiteny. 2004. The use of maize distiller’s grains with solubles in pig diets. Pig News and Information 25: 75N–83N.

USDA. 2007. Swine 2006, part 1: Reference of swine health and management in the United States, 2006. #N361.0902. USDA:APHIS:VS, CEAH, Fort Collins, CO.

Williams, A. G., E. Audsley, and D. L. Sandars. 2006. Determining the environmental burdens and resource use in the production of agricultural and horticultural commodities. Main Report. Defra Research Project ISO205. Cranfield University, Silsoe, UK.

Zhu, X., and E. C. van Ierland. 2004. Protein chains and environmental pressures: A comparison of pork and novel protein foods. Environmental Sciences 1: 254–276.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.