Sheppard, S. C., Bittman, S., Swift, M. L. and Tait, J. 2011. Modelling monthly NH₃emissions from dairy in 12 Ecoregions of Canada. Can. J. Anim. Sci. 91: 649-661. Ammonia (NH₃) from livestock manure is emitted from barns, storages and manured land, and is a loss to the farm operations, while atmospheric NH₃ has potential impacts beyond the farm, including human health and ecological damage. Models are used to estimate the intensity and spatial extent of NH₃ emissions, and this paper reports a recent model developed for quantifying emissions from the dairy sector in Canada. The estimated overall average emission to the atmosphere in Canada in 2006 was 42.4±9.0 kg NH₃ cow^-1 yr^-1 from a lactating cow, and total emission from the Canadian dairy sector was 56000 t NH₃. On many farms the NH₃ emissions may have been a significant portion of the N requirements of their crops. The emission estimates in the 12 Ecoregions were proportional to the animal census. Emissions generally peaked in May, mainly because of landspreading of manure. There were also differences in emissions per animal among the Ecoregions related to the specific practices, such as amount of grazing and injection of slurry. The sensitivity analysis suggested that a shift from the present 14% injection of slurry manure into soil to 80% may be effective overall, potentially decreasing annual emissions by 13% and emissions in May by 27%.