Enteric methane is a byproduct of feed digestion that contributes significantly to Ireland’s greenhouse gas (GHG) emissions.
Since Ireland targets to reduce greenhouse gas emissions by 25% by 2030, researchers are still busy trying to find ways to reduce methane.
A discussion took place at a recent Teagasc-led event in Portlaoise entitled ‘Agriculture and Land Use in Ireland: Pathways to a Sustainable Future’, where research undertaken to reduce methane levels was highlighted.
However, a recent report from Environmental Protection Agency (EPA) It indicates that the goals will not be achieved without changes in the use of nitrogen fertilizers and reductions in livestock numbers.
Which begs the question: Will farmers devote time, effort and money to reducing emissions, then let them reduce livestock numbers after a few years?
Methane
With 6,797 farmers applying for a nitrate exemption in 2026, the vast majority of farmers will have no choice but to work to reduce emissions, but that is easier said than done
Ireland is unique with its pasture-based dairy production system, which is great for us in the global market, but also means that we have limited research available regarding nutritional factors that influence methane production.
Researchers from Ireland and New Zealand have previously collaborated to understand how stage of lactation, pasture quality and species, management and seasonal growth affect baseline methane emissions – however, much remains to be answered.
What we do know is that methane is tied to the animal’s diet, so more needs to be done to maximize the benefits of grass.
Teagasc’s Ben Lahart said they use mathematical models to calculate how much methane is produced on Irish dairy farms.
The general calculation is as follows;
Total energy consumption x 6.3% = 355 g methane/day
However, a significant amount of work goes into obtaining this accuracy, as the feed intake profile of dairy cows in Ireland fluctuates regularly throughout the year.
The typical dry matter intake (DMI) of a cow calving in February will rise steadily for 10-12 weeks, before reaching peak DMI around mid to late April.
From here, the DMI will gradually decline for the rest of the season until the cows dry out in December.
In previous studies, Lahart noted that feed intake and TDA peak in the summer months at 18 kg DM and decline in winter at 10.6 kg DM, with the highest levels of crude protein eaten during the spring.
As for seasonality in feed intake and feed quality, according to Lahart’s study, they are as follows:
| spring | summer | autumn | winter | |
|---|---|---|---|---|
| Physiological condition | Breastfeeding | Breastfeeding | Breastfeeding | Non-breastfeeding |
| DM(kg/day) | 16.9 | 18.0 | 17.8 | 10.6 |
| Feeding type | herb | herb | herb | Grass silage |
| Crude Protein (g/kg DM) | 228 | 197 | 201 | 147 |
| Neutral detergent fiber (g/kg DM) | 417 | 439 | 449 | 560 |
| Digestibility of organic matter (g/kg DM) | 825 | 798 | 790 | 677 |
These results highlight how less methane is produced in early spring, but rises steadily from about mid-May onward.
At the same time, we see feed quality gradually deteriorating and the proportion of neutral detergent fiber (NDF) in the diet increasing.
This rise in methane production is also associated with decreased solid milk production, highlighting the effects of reduced digestibility in grassland plots.
grazing
The level of NDF in the diet appears to have a significant impact on the methane produced by the cow, along with the amount of digestible energy content and pasture quality.
Using grass and getting as much grass into the diet as possible is crucial, Lahart said.
This means working towards compact calving seasons and getting cows out on grass more days of the year, through improved grazing infrastructure, good seal covers and optimized pre-grazing grass.
Introducing cows to ideal pre-grazing covers of 1400kg DM/ha when the plant is lush, high in protein and at the three-leaf stage, should result in increased milk solids production and ultimately lower methane production, which is a win-win.
Lahart also noted how alfalfa pastures reduce the chemical N, but increase enteric methane because there is more DM.
Despite the increase in methane levels, Lahart said alfalfa is still a good move as nitrous oxide emissions are reduced more than methane levels are increased, meaning overall greenhouse gases are reduced.
Other solutions
The event also discussed further solutions that can be used to reduce methane levels.
Sinéad Moloney and Hazel Costigan of Teagasc talked about the use of anti-methanogenic feed additives such as Bovaer (3-NOP).
Bouvier is considered the most successful of these additives, but there have been question marks raised about these types of feed additives.
Teagasc’s Maeve Williams spoke about methane reduction through reproductive strategies.
The carbon sub-index was added to the EBI several years ago as a broad part of this strategy.
The potential for methane to be added to the EIE in the future exists, as William’s study found that 16% of the variation in methane production from cow to cow is rooted in genetics.
She noted that there was a 56 g/day difference in methane production between cows in the top 20% and bottom 20%, meaning there was a lot of room for improvement through breeding.
