An international consortium of animal scientists concludes that revised methane emission factors for specific regions are required to improve methane emission estimates for dairy cattle in national inventories. The scientists, including scientists from Wageningen University & Research, collated a large global database of methane production from dairy cattle, to develop intercontinental and regional models of methane emission. The results have recently been published in Global Change Biology.
Dairy cattle produce methane, a greenhouse gas with considerable impact on climate change. To reduce the impact of dairy cattle production on the environment, the amount of methane produced needs to be quantified accurately. Measurement of methane production is complex and expensive. Therefore, models are commonly used to predict methane production, and results are used in national inventories of greenhouse gas emissions.
Data of 5,200 lactating dairy cows refine enteric methane prediction
The present study is based on a dataset of measurements from over 5,200 lactating dairy cows assembled through collaboration of animal scientists from 15 countries. The core project (GLOBAL NETWORK) was developed by a consortium of 8 countries (USA, UK, The Netherlands, France, Spain, Ireland, Switzerland, and Finland) and was funded by national governments, mostly via The Joint Programming Initiative on Agriculture, Food Security and Climate Change (FACCE-JPI).
The project represents a true collaboration of animal scientists around the globe who shared their experimental data. The main goal of the project was to develop robust enteric methane prediction equations that can be used by scientists, government agencies, and non-profit organizations interested in adopting or assessing methane mitigation strategies and abating the trends in earth’s climate.
Simplified models to predict methane emission
This large study showed that methane emission from dairy cattle can be predicted by simplified models requiring readily available feed-related variables. Feed intake is the key factor for methane production prediction. Although complex models that use both feed intake and detailed chemical composition had the best performance for predicting methane production, models requiring only feed intake and dietary fibre content had the second best predictive ability, and offer an alternative to complex models.
Region specific methane conversion factors improve accuracy
A major finding is that revised methane emission conversion factors for specific regions are required to improve emission estimates in national inventories. The concept of methane emission conversion factor was introduced by the Intergovernmental Panel on Climate Change (IPCC) to indicate the proportion of the animal's energy intake converted to energy in methane. This factor is widely used for national greenhouse gas emission inventories and global research on mitigation strategies.
The research by the consortium offers opportunities to include region specific methane conversion factors in national inventories. This is essential to improve accuracy of carbon footprint assessment of dairy cattle production systems in several regions worldwide, and to help devise mitigation strategies.
The team that conducted the study is currently developing similar databases for predicting and mitigating methane emissions from beef cattle and small ruminants (sheep and goats).