Early stage trials at Teagasc Moorepark have indicated that the amount of methane produced by dairy cows grazing at pasture is greatly overestimated.
The work, which has been conducted by VistaMilk postdoctoral researcher Ben Lahart, has shown there is a disparity between the measured emissions in field and the current estimate used by the national inventory.
The current estimate is that a 550kg dairy cow grazing on pasture emits approximately 320g to 330g of methane per day.
In April, the cows in Lahart’s trial were estimated to produce 361g of methane per day. The team measured the cows to be producing just 256g of methane per day on average, almost 30% less than estimated.
During the early lactation period, it appears we may be overestimating the amount of methane our cows are producing
The current method of calculating methane for dairy cows in Ireland is using an emission factor. The emission factor is the amount of energy lost to methane which is estimated to be 6.5%.
“In March, April and May there’s quite a difference between what the cows had been calculated to produce and to what was actually measured,” Lahart told a Teagasc Research Insights webinar on Wednesday morning.
“During the early lactation period, it appears we may be overestimating the amount of methane our cows are producing. This is during the peak milk months driven by grass consumption which, in turn, appears to be driving down methane production.
“We will follow this over the course of the year to see how it averages out.”