Gaseous emissions from livestock production continue to receive increasing attention due to concerns over their environmental and health impacts. Local concerns over gaseous emissions are usually focused on odor and environmental impacts. For example, ammonia (NH3) is usually of concern for its potential negative impacts on local environments or ecological systems due to deposition, whereas greenhouse gases (GHGs) emissions are of concern for their potential impacts on global climate variability. However, it is important to understand the quantity and composition of gasses being emitted to the atmosphere. The primary GHGs associated with livestock production are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Information on GHG emissions from U.S. swine production facilities is meager, especially under commercial production conditions.
Current recommendations for swine building ventilation systems design to maintain an environment conducive to animal productivity and well-being are based on heat and moisture production rates measured in the 1950s and 1970s. Advancements in animal genetics, nutrition and management practices to increase productivity and pork quality since then likely have led to considerable changes in heat and moisture production rates of modern swine and their housing systems. Updated data are thus needed.
Therefore, the objectives of this extensive field monitoring study were to quantify the emissions of GHG and NH3 from a Midwestern production-scale breeding/gestation/farrowing facility over a one-year period and quantify the total heat production rate (THP) of the animals and the partitioning of THP into house-level latent heat or moisture production rate (LHP, MP) and sensible heat production rate (SHP) of the facility. This study will begin to establish the baseline GHG emissions and contribute to the national air emissions inventory for swine production in the United States, particularly under Midwestern production conditions, and help updating the standards for engineering design and operation of modern swine housing.
A 4300 sow capacity breeding/gestation/farrowing facility in central Iowa was used in this one-year intensive monitoring study. The facility consisted of one breeding/early gestation barn (B/EG), one late gestation (LG) barn, and two farrowing buildings with nine farrowing rooms each (40 farrowing crates per room). The farrowing rooms held manure in a shallow pit that was drained into an external storage at the end of each farrowing cycle (~21days). The B/EG and LG barns held manure in a deep pit of each barn. Manure from the barns and the external storage were pumped out twice a year.
A Mobile Air Emissions Monitoring Unit (MAEMU) was used to continuously measure variables needed to determine the gaseous emissions and heat and moisture production rates from the breeding/gestation barns and two farrowing rooms. For each monitored barn/room the following data were measured and recorded at 30-second intervals: fan running status, building static pressure, indoor air temperature and relative humidity (RH), outdoor air temperature and RH, and barometric pressure. Gaseous concentrations of the exhaust air were measured with a gas sampling system that stepped sequentially through two composite sample locations in each barn or room (8 total), 8 minutes of sampling and analysis per location to ensure collection of stabilized readings. In addition, gaseous concentrations of the ambient air or background were measured every two hours. The static pressures and fan status were used with fan specific performance curves developed with in-situ measurements to determine each fan’s airflow rate, hence the building ventilation rate.
The average daily emissions from each source – breeding/gestation barns, farrowing barns, and external manure storage – and the total farm, in pounds per 100 sows per day, is summarized in Table 1. The whole-farm had average daily emission rates, on a per 100 sows or sows+litters basis, of 3.68 lb NH3, 857 lb CO2 (of which 776 lb from animal respiration), 0.02 lb N2O, and 29.7 lb CH4. The overall farm-level GHG emission averaged 80.8 lb CO2eq/sow-day after removing CO2 due to animal respiration. Daily NH3 emissions averaged 0.03 lb/sow for the gestation phase, 0.06 lb/(sow+litter) for the farrowing phase, and 0.01 lb/(sow+litter) for the external storage, with an overall farm total of 0.037 lb/sow. Based on the daily NH3 emissions, the number of animals needed to trigger the EPCRA reporting threshold of 100 lb NH3/day is 2702 sows. Table 2 details the partitioning of the whole farm emissions to each source – breeding/gestation barns, farrowing barns, and external manure storage. As expected, NH3 emissions occur primarily where the animals are and CH4 is emitted at higher levels for longer-term and higher volume manure storage.
The measured CH4 emission rates from the LG and B/EG barns of this study (21.6 lb d-1 100 sows-1) are higher than reported values for other breeding/gestation systems (3.3 to 12.5 lb d-1 100 sows-1). The measured N2O emission rates are also higher than previously reported (0.01 vs. 0 lb d-1 100 sows-1). This is presumably due to previous measurements taken with shallow-pit barns. The deep-pit manure storage results in more CH4 and N2O production as anaerobic conditions in manure is the main source of these two gasses in swine production systems. This is further evidenced by the drastically higher CH4 emissions from the external manure storage compared to the farrowing rooms. The measured NH3 emission rates from the farrowing rooms of this study (6.5 lb d-1 100 sows-1) is slightly above the reported literature range (1.9 to 5.4 lb d-1 100 sows-1).
Results from the study (Tables 3 and 4) show that THP at 20°C averages 2.8 Btu hr-1 lb-1 for sows in the B/EG stage, 2.3 Btu hr-1 lb-1 for sows in the LG stage, and 5.0 Btu hr-1 lb-1for sows and litters in week 0 of the lactation stage. The corresponding house-level LHP for the three stages averages 1.1 Btu hr-1 lb-1 (B/EG), 0.9 Btu hr-1 lb-1 (LG), and 3.0 Btu hr-1 lb-1 (lactation, week 0). Finally the corresponding house-level SHP for the three stages averages 1.7 Btu hr-1 lb-1 (B/EG), 1.4 Btu hr-1 lb-1 (LG), and 2.0 Btu hr-1 lb-1 (lactation, week 0). Compared with the ASABE standards, values from the current study for gestation sows in their early and late pregnancy stages showed increases of 28% and 8% in THP, 53% and 22% in LHP, and 16% and 2% in SHP, respectively. Values for lactating sows and litters during the first week after parturition showed increases of 23% in THP, 48% in LHP, and -2% in SHP relative to the ASABE standards. The reductions of THP from day to night for the three stages were 32% (B/EG), 27% (LG), and 7% (lactation). These data contribute to the updating of the standards used in the design and operation of ventilation systems for modern swine breeding/gestation and farrowing facilities.
The results from this study provide emission rates for ammonia and greenhouse gases for a modern, Midwest breeding/gestation/farrowing facility. The emission rates measured will help fill the literature gap for swine production gaseous emissions. Additionally, the heat and moisture production rates measured will allow for the updating of design standards for ventilation systems in swine housing to continue to improve housing design, indoor air quality, and efficiency of resources utilization.