Reducing methane emissions within Irish grazing systems is a challenge for the sector ahead of emission reduction targets.
Irish agriculture has been set a target of reducing emissions by 25% by 2030, with methane accounting for 62.5% of Irish agricultures greenhouse gas (GHG) emissions.
Speaking at the DSM-Firmenich conference in the Killashee Hotel in Naas, research officer, Ben Lahart from Teagasc, outlined a number of key focus areas to help achieve this target.
Methane emissions
Lahart firstly noted that a lot of work is being done to calculate the methane emissions in dairy herds, but that a lot of this is being done in indoor systems.
He noted that research from Teagasc, University College Dublin (UCD) and the Agri-Food and Biosciences Institute (AFBI) shows that emissions from grazing dairy cows is different to housed systems.
According to Lahart: “When we pool this data together, the difference between the international default emission factor, and what we are actually measuring, is about 9%.
“We can’t use the 9% reduction in methane for a mitigation measure – we can’t say we have reduced our emissions.
“Cows in Ireland have always been grazing grass, so that means that their methane output has always been over estimated.
“What it does mean is that, we need to reduce our emissions by 25% or a smaller number – so that will help to some degree and it would help to reduce the carbon footprint of Irish milk.
“In saying that, we still need to reduce our emissions with a specific focus on methane.”
Grass quality
Lahart explained that Teagasc are now looking into two key pillars in the hopes of reducing emissions.
The first pillar is pasture or grazing management. Lahart added: “We know utilising spring grass can help reduce methane output.”
He explained that methane output during spring is lower in comparison to other times of the year.
Increasing the amount of spring grass that is grazed by cows, and having cows calving down earlier in the year to eat this grass, can reduce methane emissions.
Lahart said this can be offset somewhat by ensuring that cows are grazing swards at the correct covers.
1,400-1,600kg of dry matter (DM)/ha should be the target during the mid-season to ensure that sward quality remains high.
To achieve this on farm, grass quality data is needed: “We need to have the measurements of grass quality on farms to relate it back to the models and so we can get credit for it nationally,” he said.
Breeding
The second pillar that is being looked at to reduce emissions from the sector is breeding and the use of the economic breeding index (EBI).
Lahart outlined a trial that was completed by Teagasc which looked at a group of high or elite EBI (€233) cows and a group of national average EBI (€133) cows.
The trial found there was no significant difference in milk yield between the elite and national average.
However, the elite group had greater milk fat and protein percentages, which resulted in an 8% greater milk solids yield compared to the national average group.
However, the increased milk solids yield of the elite group resulted in a dilution of their methane emissions on a unit of output basis, which resulted in 7% less methane/unit of milk solids.
Lahart said that the calculated methane from the elite group was significantly higher compared to the national average group – which is driven by the increased milk solids output.
“As we go forward and increase productivity nationally through breeding indexes, we may potentially increase methane output on paper, or in the calculations – but on the ground, that might not actually be happening.
“We are going to continue this work and continue looking at the data, but there may need to be a correction within the inventory to ensure that high genetic animals are not being penalised.”
Lahart also noted that there may be potential to directly select lower methane output in the EBI.
The final pillar that is being focused on, is feed additives.
It was noted by Lahart that a number of trails have seen positive results.
But, he said the question remains as to ‘how they can be effective within grazing systems over a longer period, between milkings?’.