Milk from grass-based grazing systems is still the most environmentally friendly, despite the higher greenhouse gas emissions that are associated with the digestion of grass compared to concentrates.
Delegates at the Alltech- sponsored Dairy Solutions Symposium in UCD heard how dairying has reduced its greenhouse gas emissions per litre of milk by more than 60pc since the middle of the last century through improved efficiencies.
However, delegates were told that further reductions will be one of the key priorities of the EU Commission over the coming decades.
Michael Hamell, who is the head of the agriculture unit in the Commission's environment division, said that the industry needed to increase the pace of emission reductions.
"The EU aims to reduce greenhouse gas emissions by 80pc by 2050," he explained.
"That will certainly involve changes not yet imagined and agricultural research and practice will need to be in high gear."
Referring to looming CAP reform negotiations, Mr Hamell said that "upcoming regulatory reviews will provide the opportunity to reflect further on this issue."
High-input dairy industries such as the dairy sector in the US are now looking to anti-microbials such as ionophores to increase feed efficiency and reduce greenhouse gas emissions from cows.
However, there is an ongoing debate on which is the best method to calculate greenhouse gas emissions from dairying.
The Intergovernmental Panel on Climate Change (IPCC) only includes emissions generated at a sector or country level.
Teagasc's Dr Donal O'Brien said that under the IPCC calculation, high input dairy systems in Ireland would have an 8pc lower carbon footprint compared to grass-based systems.
This is due to the lower methane emissions from non-structural carbohydrates, such as concentrates, compared to high-fibre diets such as grass.
However, the IPCC calculation omits all emissions associated with imported feed such as soya, which could account for 30pc of the carbon footprint of high-input systems where cows are confined indoors and up to 50pc of the total feed intake is based on concentrates, according to Mr O'Brien.
Mr O'Brien stated that a more appropriate measure was the Life Cycle Assessment (LCA) method where all emissions are included in the calculation, irrespective of their origin.
Using the LCA methodology, Mr O'Brien's research showed that the high-input system had a carbon footprint which was 16pc higher than a grass-based system per kilogramme of milk solids.