Biogenic and fossil main greenhouse gas emissions of dairy, beef, pig and poultry systems

Conventional analyses of the carbon footprint of livestock systems do not consider the relationships between the characteristics and sources of each greenhouse gas (GHGs; CH₄, N₂O, CO₂) and the different livestock systems. This study aimed to assess the carbon footprint of a variety of livestock systems, including different animal categories (dairy cattle, beef cattle, pig and poultry) and production circumstances (lowland and mountain areas). An attributional cradle-to-gate-of-the-farm Life Cycle Assessment was used, considering the emission pattern of each GHG and distinguishing fossil and biogenic origins. The production stages included animal and manure management, on- and off-farm feed production and the production and use of the farm materials. The functional unit was 1 kg of crude protein in animal food (CPAF). Emissions per single GHG and production stage were analysed with a general linear model which included the effect of the livestock system, which proved to significantly influence the emission pattern of all GHGs, both in absolute terms (kg/kg CPAF) and with respect to the single production stage. The CO₂ (fossil-based) resulted as the most emitted GHG (10.2-27.6 kg/kg CPAF), 10-255 and 284-646 times greater than CH₄ and N₂O, respectively. Methane was found to be more associated with the animal category (ruminants), whereas N₂O and CO₂ were more associated with the input intensity level. Livestock systems strongly influenced the biogenic GHG emissions but not the fossil-related one, with dairy, pig and poultry systems showing similar and lower values than beef. In conclusion, the evaluation of the pattern of each GHG as well as of their biogenic or fossil origin can give indications to address the reduction of global warming.