Understanding greenhouse gas emissions in pasture-based systems

About the research

The four-year programme is running from 2024 to 2028 and will see research partners working together to quantify methane emissions from dairy cows in pasture-based systems.

The programme will also develop methane emissions factors for pasture-based systems to ensure emissions and mitigations are accurately accounted for at a farm and national level in NZ and Ireland. Both countries face national and market targets to reduce methane.

The aim is to determine the effect stage of lactation and pasture species, management and seasonal growth have on base methane emissions, and how these factors influence cows’ responses to methane-reducing technologies.

Project status: progressing

Why we’re doing it

Currently in greenhouse gas 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 21.6 g 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.

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 baseline emissions from a pasture-based diet and understand whether the variation in methane is due to the pasture itself or connected to cows being in early lactation.

Where we're at on progress

Read more on the result of the trial so far.

Trial 1: Measuring methane from cows grazing pastures during the season (New Zealand)

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.

Trial 2: Measuring methane from cows grazing pastures (Ireland)

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.

Partnering with farmers

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’re excited about our continued work alongside farmers and other sector and research organisations to develop mitigation solutions for our unique pasture-based farm systems – and to get ahead of the environmental challenges farmers face.

The impact this research will have

By understanding the factors behind the differing responses of grazing cows, we can develop technology specifically tailored to pasture-based systems and optimise its use throughout the season.

The joint programme strengthens our connection with Ireland and enables NZ to leverage current and future research. It also fits within DairyNZ’s wider research programme.

Read more about DairyNZ’s larger programme of work for reducing greenhouse gas here.

This wider programme sees world-leading scientists working with NZ farmers, research organisations and commercial companies to develop workable and scalable mitigation solutions that can be widely adopted on-farm to reduce emissions in a sustainable and viable way.

Research partners

This collaboration will include researchers, students, professors and database technology experts from DairyNZ (NZ) and Ireland’s Agriculture and Food Development Authority (Teagasc), University College Cork and Irish Cattle Breeding Federation.

How is this project funded?

DairyNZ was awarded funding in 2023 for this work, 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.

The research occurring in Ireland is funded by the Department of Agriculture, Food, and the Marine (DAFM).