Whole Farm Decision-Making, Dairy Farms Profitability and Greenhouse Gas Emissio

The dairy industry has been under the spotlight for the greenhouse gas (GHG) emission. Methane and Nitrous oxide are the two major GHG in a dairy farm. As a ruminant, dairy cows produce methane from the rumen microbial activities. Manure management is another major emission source of methane and nitrous oxide on a dairy farm. Feed production on-farm and off-farm are associated with nitrous oxide and methane emission. Previous research has studied many GHG mitigation options through nutritional management, grazing management, genetic selection, however, not much research has been conducted on herd management. The dissertation estimates the effect of different management strategies and the interaction between strategies on dairy farms GHG emission intensity (kg CO2 eq. per unit of milk) and profitability simultaneously with farm-level life cycle assessment models.;Results confirmed previous research suggesting that increasing milk production is the ultimate approach to reducing dairy farm GHG emission intensity. Higher replacement rate increases farm-level GHG emission due to the greater number of replacement animal needed. However, the higher meat production due to higher replacement rate also reduces the farm-level GHG emission allocation to milk production. Greater milk productivity improvement may counterbalance the effect from higher replacement rate on enteric methane emission in a long-term. Feeding strategies and diet formulation (i.e. extensive grazing, higher concentrate feed, etc.) influenced on all the 3 major emission sources (enteric fermentation, manure management, and feed production). Mitigation strategies that focus on enteric methane emission (such as diet formulation changes) may have a carryover effect on manure GHG emission and crop production emission. Selection of the functional units in the LCA also changes the evaluation of different strategies.