Abstract
Before recommending a feeding strategy for greenhouse gas (GHG) mitigation, it is important to conduct a holistic assessment of all related emissions, including from those arising from feed production, digestion of these feeds, managing the resulting manure, and other on-farm production processes and inputs. Using a whole-systems approach, the Holos model, and experimentally measured data, this study compares the effects of alfalfa silage- versus corn silage-based diets on GHG estimates in a simulated Canadian dairy production system. When all emissions and sources are accounted for, the differences between the two forage systems in terms of overall net GHG emissions were minimal. Utilizing the functional units of milk, meat, and total energy in food products generated by the system, the comparison demonstrates very little difference between the two silage production systems. However, the corn silage system generated 8% fewer emissions per kg of protein in food products as compared to the alfalfa silage system. Exploratory analysis of the impact of the two silage systems on soil carbon showed alfalfa silage has greater potential to store carbon in the soil. This study reinforces the need to utilize a whole-systems approach to investigate the interrelated effects of management choices. Reported GHG reduction factors cannot be simply combined additively because the interwoven effects of management choices cascade through the entire system, sometimes with counter-intuitive outcomes. It is necessary to apply this whole-systems approach before implementing changes in management intended to reduce GHG emissions and improve sustainability.
Highlights
The livestock industry is challenged with reducing greenhouse gas (GHG) emissions to limit the negative impacts of climate change
70–85% of total GHG emissions associated with milk consumption in industrialized countries can be attributed to activities on the farm (i.e., “cradle-to-farm gate emissions” [3,4])
This highlights the opportunity for dairy producers to make management choices that can significantly reduce the overall carbon footprint or GHG intensity (e.g., sum of GHG emissions and removals expressed relative to a kilogram of fat and protein corrected milk (FPCM)) of dairy products
Summary
The livestock industry is challenged with reducing greenhouse gas (GHG) emissions to limit the negative impacts of climate change. 70–85% of total GHG emissions associated with milk consumption in industrialized countries can be attributed to activities on the farm (i.e., “cradle-to-farm gate emissions” [3,4]). This highlights the opportunity for dairy producers to make management choices that can significantly reduce the overall carbon footprint (e.g., sum of GHG emissions and removals in a product system) or GHG intensity (e.g., sum of GHG emissions and removals expressed relative to a kilogram of fat and protein corrected milk (FPCM)) of dairy products. Farm-based life cycle assessments of Canadian dairy production have identified methane (CH4 ), mostly from enteric fermentation, as the largest source of GHG from dairy farms [7,8]
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