The key hypothesis was that NH3 emission rates vary across Ecoregions and over time in a way that affects the degree of impact. The survey showed many differences across Ecoregions, most importantly related to feed crude protein and landspreading practices.
The model estimated that grower pigs (>20 kg to market size) excreted on average about 8.5 kg total ammoniacal N (TAN) per (occupied) pig place per year, and based on the national average farm practices, 25% of this TAN was emitted from barns, 5.3% was emitted from manure storage, and 17% was emitted during landspreading for a total of 4.8 kg NH3 pig-place-1 yr-1. The total loss for grower pigs ranged from 40 to 53% of excreted TAN across the 12 Ecoregions. Nursing sows emitted over twice as much per pig. Regions varied in reliance on homegrown feeds, which affected crude protein feeding and TAN excretion rates. Western regions had relatively low emissions from land application of slurry because of more extensive use of injectors. Emissions from grower pigs in winter were about 0.2 kg NH3 pig-place-1 month-1, mostly from barns, to as high as 0.7 kg NH3 pig-place-1 month-1 in May, mostly from landspreading. Total emission for all of Canada in 2006 was 73 × 106 kg NH3 or about 13% of agricultural emissions in Canada.
The results indicate that emission reductions can be achieved with greater use of low-emission application methods and reduced crude protein in feed. The emissions model can be used in future to assess the impacts from changes in feeding regimes and barn designs, and changes in practices such as animal density and increased access to outdoor spaces.
S.C. Sheppard, S. Bittman, M.-L. Swift, and J. Tait. Farm practices survey and modelling to estimate monthly NH3 emissions from swine production in 12 Ecoregions of Canada. Canadian Journal of Animal Science. 2010. Vol. 90 (2): 145-158.