Improving the sustainability of the United States’ (US) pork supply chain requires a better understanding of the relationship between the environment and production practices. Pork producers play a crucial role in environmental stewardship, however, the impact of production efficiency on greenhouse gas (GHG) emission has not been well-established. Interpreting the influence of specific production metrics on GHG emission is essential for benchmarking and improving the environmental sustainability of the pork industry.
During their growth period, pigs generate three major greenhouse gases: carbon dioxide, methane, and nitrous oxide. Carbon dioxide is produced as a byproduct of maintenance and growth and is emitted through exhalation during respiration. Methane and nitrous oxide are generated primarily by manure and are dependent on the type of manure management system implemented in the barn. The wean-to-finish sustainability calculator was designed to provide farmers with a tool to estimate the impacts of various levels of production efficiencies (feed efficiency and mortality), allowing them to determine how specific improvements in finishing can influence the environmental footprint. The calculator provides insight into GHG emissions at the individual barn level to enable continuous
improvements in the pork industry.
Sources of Greenhouse Gas Production
From the Pig
An equation for carbon dioxide production from respiration was previously published by Philippe and Nicks. The boundaries of this equation were expanded using the slope to satisfy the weight range of finishing pigs. The Intergovernmental Panel on Climate Change (IPCC) established guidelines and equations for methane and nitrous oxide production for specific swine manure management systems. Two manure management systems for swine production were taken into consideration: deep pit and anaerobic lagoon. Two timepoint selections were used only for deep pit: deep pit storage greater than one month and deep pit storage less than one month . Methane and nitrous oxide were converted to their carbon dioxide equivalents using their global warming potential: methane (25) and nitrous oxide (298).
From the Diet
The GHG contributions from the diet were estimated using wean to finish diet formulations reported by Thoma’ et al. Ingredients included corn, soybean, and dried distillers grain. Corn and soybean GHG emissions are estimated by the amount of carbon dioxide equivalents produced for a bushel of product, and do not include feed processing. Ingredient percentage was multiplied according to dry matter intake. The quantity of the ingredient was multiplied by the carbon footprint for the production system. Dried distillers grain was modeled using the EcoInvent unit processer specific for US conditions reported by Thoma’ et al. The carbon footprint accounts for fermentation, drying, and other processes that are standard of US corn ethanol plants.
Wean-to-Finish Production Metrics
Data was collected for baseline closeout weight and days in the barn until market. Baseline average daily gain, dry matter intake, and feed efficiency curves were obtained. A mortality equation was designed to assume production of GHG from respiration, feed, and manure management system; this was calculated only for the period of time the animal is alive.
Total GHG emissions are sourced from the amount of gas emitted by live and dead pigs. Estimates for GHG production by live pigs follows the assumption that the pig reached market weight (281 pounds). Estimates for GHG production by pigs that died follows the assumption that the pig reached the halfway point (140.5 pounds). Barn size and mortality rate is set by the user.
Summary
From these assumptions, GHG emissions can be calculated based on mortality, manure management systems, feed efficiency, and feed type; all of which can be applied within specific production parameters set by the user. The calculator can be manipulated to compare current production practices and target closeouts for the barn. A percent change is generated to demonstrate the potential improvement or decline of the different production metrics’ influence on emissions; the calculator is free to download from the Iowa Pork Industry Center website (ipic.iastate.edu/information /WFPorkSustainabilityCalculator.xlsx). To evaluate the assumptions used within this calculator, sensitivity analyses were conducted for mortality (Table 1), feed efficiency (Table 2), and feed type (Table 3).
References
Dong, H., J. Mangino, T. A. McAllister, J. L. Hatfield, D. E. Johnson, D. Bartram, D. Gibb, and J. H. Martin. 2020. 2006 IPCC Guidelines for National Greenhouse Gas inventories – Chapter 10: Emissions from livestock and manure management.
MetaFarms Production Index: Nursery, Finishing, Wean-to-Finish Closeout Performance, and Market Hog Sales. 2019.
PIC 2019 Wean to Finish Guidelines. 2019. Hendersonville.
Philippe, F. X., and B. Nicks. 2014. Review on greenhouse gas emissions from pig houses: Production of carbon dioxide, methane and nitrous oxide by animals and manure. dx.doi. org/10.1016/j.agee.2014.08.015 Agriculture, Ecosystems and Environment 199:10–25. doi:10.1016/j.agee.2014.08.015.
Thoma, G., D. Nutter, R. Ulrich, M. Charles, J. Frank, and C. East. 2011. National Life Cycle Carbon Footprint Study for Production of US Swine. 1-75.
Thomson, A., E. Coronel, and K. Young. 2021. Field to Market: The Alliance for Sustainable Agriculture. Environmental Outcomes from On-Farm Agricultural Production in the United States. 4th edition.
Understanding Global Warming Potentials. 2021. United States Environ. Prot. Agency. Available from: epa.gov/ghgemissions/understanding-global-warming-potentials.
