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

Context . Enteric methane (CH 4 ) 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 CH 4 emissions and emission intensity (EI) of milk production across these systems. Aims . The objective was to estimate the lactating cows ’ enteric-CH 4 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-CH 4 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-CH 4 emissions of Farms A and B (13.1 and 12.9 kg CO 2 e/head.day respectively) were greater than those of Farms C and D (11.7 and 11.6 kg CO 2 e/head.day respectively). Furthermore, CH 4 EI was greater in Farms C and D (0.49 and 0.48 CO 2 -e kg/kg fat-and protein-corrected milk (FPCM) respectively) and it was lower in both Farms A and B (0.46 CO 2 -e kg/kg FPCM). Overall, Farms A and B using Feeding-system 4 – 5 with greater-producing cows produced more CH 4 but with less CH 4 EI than did the Farms C and D, which are mainly pasture-based. Conclusions . These fi ndings suggest that to reduce CH 4 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 CH 4 emissions, which helps address climate change. Implications . EstimationofCH 4 emissions,EI and seasonal changes inthem gives farmersthe opportunity to identify the mitigation strategies and plan speci fi c strategies that fi t the particular feeding system and season. However, more research needs to be conducted to check the feasibility of doing this.