Scientists are delving into the complexities of methane emissions from grazing cows, aiming to develop more precise emission factors and mitigation strategies for our unique pasture-based systems.
Inside Dairy
3 min read
A collaborative research programme with Ireland is focusing on understanding and accounting for methane emissions from pasture-based dairy systems.
To support farmers in reducing greenhouse gas (GHG) emissions , DairyNZ has teamed up with Irish researchers to quantify methane emissions from dairy cows in pasture-based systems. The four-year programme, Emissions4Pasture, sees research happening across both countries to share knowledge and gain a deeper understanding.
Researchers, students, professors and database technology experts from DairyNZ and Ireland’s Agriculture and Food Development Authority (Teagasc), University College Cork and the Irish Cattle Breeding Federation will be working together to quantify methane emissions from grazing dairy cows.
Currently in GHG inventories, a standard methane emissions factor is used for all feed eaten by the dairy cow. In New Zealand, this factor predicts that for every kilogram of dry matter that a cow eats, it produces 21.6g of methane. A similar approach is used in Ireland.
Although feed is a major factor driving methane emissions, not all feeds are created equal – different types, qualities and amounts of feed lead to varying levels of methane production. We are interested in exploring how this plays out within our pasture-based system.
The Emissions4Pasture programme is exploring how different types, quality, and seasonality of pasture can impact methane emissions within pasture-based systems.
Recent research from Ireland supports this variation, showing that cows grazing in spring produce less methane than expected based on inventory calculations, and less than they do in summer and autumn. We aim to see if we can replicate these results in NZ and determine whether the variation in methane is due to the pasture itself or connected to cows being in early lactation.
This will involve using two herds at one of the DairyNZ research farms in Hamilton, an autumn-calving herd and a spring-calving herd. Starting in August 2024, we are measuring methane emissions from these herds for 12 months while they are outdoors grazing pasture. At four times, spring, summer, autumn and winter, a subset of each herd will be brought into our indoor facilities to measure methane and feed intake while still consuming fresh pasture.
Using these two herds of cows lets us see how both the cow and the pasture affect methane emissions. For example, in September/October, we will have cows in early lactation and late lactation all eating spring pasture, and in March/April we will have cows in early lactation and late lactation eating autumn pasture.
Using two herds of cows lets us see how both the cow and the pasture affect methane emissions.
Grazing cow trials are also planned for Ireland. Beginning in spring 2026 (February), these trials will explore how different pasture species affect methane emissions and whether pasture management practices have an impact.
Through the Emissions4Pasture programme, we hope to gain a better understanding of baseline methane emissions from a pasture-based diet. We’re also aiming to understand how cows in these systems respond to mitigation strategies such as feed additives. Early data indicates that responses can vary depending on the season, the amount of feed or the type of diet the cows are on.
If this collaborative research programme helps us identify the reasons behind the variation in grazing cows’ responses, we can develop technology tailored to pasture-based systems and optimise its use throughout the season.
For example, if we find that feed additives aren’t as effective in spring, when farmers typically use fewer supplements and it’s harder to administer additives to the animals, those additives could be reserved for another time of the season when they would be more effective and easier to use.
The ultimate output of the programme is to develop a methane database for pasture-based systems, aimed at accurately accounting for emissions and mitigation efforts at both the farm and national levels in NZ and Ireland. While we can’t guarantee this outcome, the data should still guide inventory planning and management.
Most of the research on methane mitigation technologies is completed at Lye Farm, one of DairyNZ’s two Waikato research farms. Lye and Scott farms are an important sector resource, enabling scientists to carry out pasture, animal, farm systems and environmental trials under relevant conditions. This ensures the technologies and tools developed are practical and can be widely adopted into different farm systems.
Scientists hope to understand how pasture quality, species and management affect on-farm emissions, and to optimise the cow response to methane mitigations.
Finding solutions to help farmers reduce emissions while maintaining on-farm profit remains a research priority for DairyNZ.
DairyNZ was awarded funding by the Ministry for Primary Industries (MPI) and the New Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC) under the Pilot Joint Research Initiative between New Zealand and Ireland.
Farmers are actively involved in all the projects, to provide their thoughts and advice on opportunities or barriers for adoption of these solutions into NZ farm systems. We are excited about our continued work alongside farmers and other sector and research organisations to understand emissions from grazing cows and to develop mitigation solutions for our unique pasture-based farm systems – and to get ahead of the environmental challenges farmers face.
For more information visit dairynz.co.nz/pasture-emissions
We are also working on improving methodologies for predicting dry matter intake in grazing animals, as current approaches in NZ aren't yielding reliable results. The aim is to develop methods that allow for the measurement of intake while cows are grazing outdoors. This is more cost effective and resource efficient than bringing animals into our indoor facilities.
This article was originally published in Inside Dairy November 2024-January 2025.
