New insights into methane emissions from dairy farms

A comprehensive review highlights the drivers of methane emissions and explores strategies to reduce them in pasture-based dairy systems. The research, led by Teagasc scientists, is vital for Ireland’s agricultural climate commitments and greenhouse gas reduction targets.

Ireland’s Climate Action Plan sets ambitious targets, aiming to cut greenhouse gas emissions by 51% by 2030, with agriculture expected to reduce emissions by 25% from 2018 levels. Agriculture currently accounts for about 39% of national emissions, with methane contributing nearly 29% of total greenhouse gases, mostly from enteric fermentation in dairy cows.

Understanding Methane Emissions in Dairy Systems

Enteric methane arises naturally when microbes in the rumen break down feed, releasing methane mainly through belching. Measuring methane on farms at scale remains difficult, so models estimate emissions using standardised conversion factors linked to feed intake energy. Recent advances in measurement technologies and studies by Teagasc, Wageningen University, and Dairy NZ indicate that actual methane emissions from grazing dairy cows may be lower than previously estimated.

Mitigation options

Several approaches are being investigated to reduce methane output:

Feed additives like Asparagopsis spp and 3-NOP can reduce methane by 20-40% in housed systems but show lower effectiveness in grazing due to dosing challenges.
Vaccines targeting methanogens are under development but require further proof of effectiveness in real-world conditions.
Genetic selection offers promising long-term reductions, with cows bred for high production not necessarily increasing methane output, potentially cutting emissions per milk unit by 0.5-1% annually.
Grazing management plays a crucial role; high-quality spring grass leads to significantly lower emissions than summer or autumn forage. Early turnout and reduced silage feeding in spring also help.
Maintaining digestible swards at about 1,400 kg DM/ha pre-grazing optimises methane reductions and lessens concentrate feed needs, lowering off-farm emissions.
Mixed-species swards incorporating clover, plantain, and chicory show potential for reducing methane relative to milk production, though results vary.

The review emphasises that while baseline methane emissions may be less than current models suggest, implementing effective, practical mitigation strategies in pasture-based systems remains complex but essential for meeting Ireland’s climate targets. For full details, see the publication: Enteric methane emissions and mitigation strategies within pasture-based dairy systems.