Canola Meal versus Soybean Meal as Protein Supplements in the Diets of Lactating Dairy Cows Affects the Greenhouse Gas Intensity of Milk

Simple Summary Soybean meal (SBM) and canola meal (CM) are routinely used as protein supplements in lactating dairy cow diets and an enteric methane-mitigating effect was recently reported for CM compared with SBM. Farm-gate life cycle assessments of milk production in eastern and western Canada were conducted to determine whether using CM rather than SBM in lactating dairy cow diets decreases greenhouse gas emissions (CO(2)e) per kilogram of fat and protein corrected milk (GHG intensity), and whether the decrease in emission intensity of milk depends upon where the meals are produced. We concluded that protein source, location of producing the meals, and the methane-mitigating effect of CM influenced the GHG intensity of milk. CM was a GHG mitigation strategy, lowering GHG intensity of milk by up to 6.6% when it was produced in western Canada, with a low up-stream emission factor and a methane mitigating effect (i.e., low Y-m value). We conclude that the emissions associated with imported protein sources affect whether they decrease the GHG intensity of milk production when included in lactating cow diets. Soybean meal (SBM) and canola meal (CM) are protein supplements used in lactating dairy cow diets and, recently, an enteric methane-mitigating effect (i.e., lower Y-m value) was reported for CM. Before recommending CM as a greenhouse gas (GHG) mitigation strategy, it is necessary to examine the net impact on total GHG emissions from milk production. The objective was to determine whether using CM rather than SBM in lactating dairy cow diets decreases GHG per kilogram of fat and protein corrected milk (FPCM), and whether the decrease depends upon where the meals are produced. Cradle to farm-gate life cycle assessments were conducted for a simulated dairy farm in eastern (Quebec) and western (Alberta) Canada. Scenarios examined the source of protein meal, location where meals were produced, and the methane-mitigating effect of CM. The Holos model was used to estimate GHG emissions from animals, manure, crop production, imported feeds, and energy use. GHG intensities (CO(2)e/kg FPCM) were 0.85-1.02 in the east and 1.07-1.11 in the west for the various scenarios, with enteric methane comprising 34 to 40% of total emissions. CM produced in western Canada with a low up-stream emission factor and low Y-m value reduced CO(2)e/kg FPCM by 3% (western farm) to 6.6% (eastern farm) compared with SBM. We conclude that using CM rather than SBM in the diet of lactating dairy cows can be a GHG mitigation strategy depending upon where it is produced and whether it decreases enteric methane emissions.