Energy and nutrient cycling in pig production systems
United States pig production is centered in Iowa and is a major influence on the economic and ecological condition of that community. A pig production system includes buildings, equipment, production of feed ingredients, feed processing, and nutrient management. Although feed is the largest single input into a pig production system, nearly 30% of the non-solar energy use of a conventional--mechanically ventilated buildings with liquid manure handling--pig production system is associated with constructing and operating the pig facility. Using bedded hoop barns for gestating sows and grow-finish pigs reduces construction resource use and construction costs of pig production systems. The hoop based systems also requires approximately 40% less non-solar energy to operate as the conventional system although hoop barn-based systems may require more feed. The total non-solar energy input associated with one 136 kg pig produced in a conventional farrow-to-finish system in Iowa and fed a typical corn-soybean meal diet that includes synthetic lysine and exogenous phytase is 967.9 MJ. Consuming the non-solar energy results in emissions of 79.8 kg CO2 equivalents. Alternatively producing the same pig in a system using bedded hoop barns for gestating sows and grow-finish pigs requires 939.8 MJ/pig and results in emission of 70.2 kg CO2 equivalents, a reduction of 3 and 12% respectively. Hoop barn-based swine production systems can be managed to use similar or less resources than conventional confinement systems. As we strive to optimally allocate non-solar energy reserves and limited resources, support for examining and improving alternative systems is warranted.