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A case study of the carbon footprint of milk from high-performing confinement and grass-based dairy farms
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2014-03
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D. O’Brien, J.L. Capper, P.C. Garnsworthy, C. Grainger, L. Shalloo, A case study of the carbon footprint of milk from high-performing confinement and grass-based dairy farms, Journal of Dairy Science, 2014, Volume 97, Issue 3, 1835-1851. doi: https://doi.org/10.3168/jds.2013-7174
Abstract
Life-cycle assessment (LCA) is the preferred methodology
to assess carbon footprint per unit of milk.
The objective of this case study was to apply an LCA
method to compare carbon footprints of high-performance
confinement and grass-based dairy farms. Physical
performance data from research herds were used to
quantify carbon footprints of a high-performance Irish
grass-based dairy system and a top-performing United
Kingdom (UK) confinement dairy system. For the US
confinement dairy system, data from the top 5% of herds
of a national database were used. Life-cycle assessment
was applied using the same dairy farm greenhouse gas
(GHG) model for all dairy systems. The model estimated
all on- and off-farm GHG sources associated
with dairy production until milk is sold from the farm
in kilograms of carbon dioxide equivalents (CO2-eq)
and allocated emissions between milk and meat. The
carbon footprint of milk was calculated by expressing
GHG emissions attributed to milk per tonne of energycorrected
milk (ECM). The comparison showed that
when GHG emissions were only attributed to milk, the
carbon footprint of milk from the Irish grass-based system
(837 kg of CO2-eq/t of ECM) was 5% lower than
the UK confinement system (884 kg of CO2-eq/t of
ECM) and 7% lower than the US confinement system
(898 kg of CO2-eq/t of ECM). However, without grassland
carbon sequestration, the grass-based and confinement
dairy systems had similar carbon footprints per
tonne of ECM. Emission algorithms and allocation of
GHG emissions between milk and meat also affected
the relative difference and order of dairy system carbon
footprints. For instance, depending on the method
chosen to allocate emissions between milk and meat,
the relative difference between the carbon footprints of
grass-based and confinement dairy systems varied by
3 to 22%. This indicates that further harmonization of
several aspects of the LCA methodology is required to
compare carbon footprints of contrasting dairy systems.
In comparison to recent reports that assess the carbon
footprint of milk from average Irish, UK, and US dairy
systems, this case study indicates that top-performing
herds of the respective nations have carbon footprints
27 to 32% lower than average dairy systems. Although
differences between studies are partly explained by
methodological inconsistency, the comparison suggests
that potential exists to reduce the carbon footprint of
milk in each of the nations by implementing practices
that improve productivity.