Comparative enteric-methane emissions of dairy farms in northern Victoria, Australia

Abstract

Context Enteric methane (CH4) is a source of greenhouse gas (GHG) in agriculture, which needs to be reduced. A variety of feeding systems for dairy production is being used in south-eastern Australia, but there are few studies that compare CH4 emissions and emission intensity (EI) of milk production across these systems. Aims The objective was to estimate the lactating cows’ enteric-CH4 emissions, EI and their seasonal changes, across different feeding systems in northern Victoria, Australia. Methods A Tier 2 inventory methodology was used to estimate the enteric-CH4 emissions and EI. Four case-study farms were selected to represent a range of feeding systems, Farms A, B, C and D were categorised as System 4–5 (hybrid–total mixed ration system), System 4 (hybrid system), System 2 (moderate–high bail system) and System 2 respectively. Monthly feed, animal and production data were sourced from June 2019 to May 2020. Key results Average enteric-CH4 emissions of Farms A and B (13.1 and 12.9 kg CO2e/head.day respectively) were greater than those of Farms C and D (11.7 and 11.6 kg CO2e/head.day respectively). Furthermore, CH4 EI was greater in Farms C and D (0.49 and 0.48 CO2-e kg/kg fat- and protein-corrected milk (FPCM) respectively) and it was lower in both Farms A and B (0.46 CO2-e kg/kg FPCM). Overall, Farms A and B using Feeding-system 4–5 with greater-producing cows produced more CH4 but with less CH4 EI than did the Farms C and D, which are mainly pasture-based. Conclusions These findings suggest that to reduce CH4 EI requires a move towards Feeding-system 4–5. However, on the basis of the results of the current study, pasture-based systems have an advantage over hybrid/total mixed ration feeding systems, as these farms have lower absolute CH4 emissions, which helps address climate change. Implications Estimation of CH4 emissions, EI and seasonal changes in them gives farmers the opportunity to identify the mitigation strategies and plan specific strategies that fit the particular feeding system and season. However, more research needs to be conducted to check the feasibility of doing this.