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What is meant by a "stable cattle herd"? [CCAC Carbon Budgeting Fellowship Blogpost 2]

posted 8 Feb 2021, 05:29 by Paul Price   [ updated 9 Feb 2021, 04:25 ]
  • The Ag Climatise roadmap, Government’s plan to reduce agricultural emissions, is premised on a “stable herd”, but no reference year or level has yet been stated. 

  • Crucially, the total herd number of beef and dairy animals does not provide meaningful information for climate action policy as dairy cows have much greater greenhouse gas emissions than beef animals. Also, within the total, the ratio of dairy to beef numbers changes through time. 

  • A more useful gauge is to state the reference year and GHG target level, then assess relative dairy and beef cattle numbers based on their annual per head emissions.

  • A straightforward calculation, based on the EPA 2020 National Inventory Report (NIR) data, indicates that annual total cattle methane has risen by 1.15 MtCO2eq since 2005, which is the reference year for mitigation of non-traded emissions. In terms of methane, for a stable herd relative to 2005, a reduction of 362,000 dairy cows or 940,000 beef cattle would be necessary to compensate for the rise in cattle methane emissions. 

  • To maintain a “stable herd” of cattle in Ireland by stabilising methane emissions from 2018, every addition of 10 dairy cows would equate to requiring a reduction in the beef numbers of 26 animals.

  • The new 2021 Inventory available in April will update dairy cow and beef per head figures for methane emissions and nitrogen excretion, so this blogpost will need to be updated to allow for the EPA recalculation.

Climate action and agriculture

Ireland has a comparatively large fraction of greenhouse gases (GHGs) from agriculture, particularly the potent global warming gases nitrous oxide (N2O) and methane (CH4). Predominantly this climate pollution is related to the number of dairy and beef cattle, which are significant sources of methane and nitrous oxide. These emissions are correlated with the level of nutrient inputs, particularly reactive nitrogen from chemical fertiliser used to boost grass growth and in concentrate feeds. The Irish government’s recently published Ag Climatise ‘roadmap’ states:

“It is well understood that emissions in agriculture have two key drivers – livestock numbers and fertiliser use.”

Although not directly referenced in the Ag Climatise document itself, the Government has strongly asserted that “the Ag Climatise roadmap is based on the premise of a stable herd”. By contrast the Climate Change Advisory Council has advised that “[a] reduction in the national herd is necessary to reduce absolute greenhouse gas emissions” (CCAC, 2019). The idea of a stable herd has now become a contentious topic in agricultural policy discussion in regard to the possible need for cap or reductions in cattle numbers. 

This blogpost (to be updated based on 2021 EPA data to be released in March) takes a preliminary look in methane-only terms at how we could calculate a "stable cattle herd" in a ‘climate smart’ way relative to a given baseline year.

At least, three important questions arise in regard to the assertion of a stable herd as a premise for climate action: 

  1. What year are we using as a benchmark for stable herd in respect to climate action?

    • 2005 is the EU reference year basis for non-traded emissions including agriculture. Given the Ag Climatise emphasis is on reducing GHGs in accord with EU policy it makes sense to use 2005 as the basis for assessing Irish agricultural emissions.

  2. Given the big difference in GHG emissions between beef and dairy cattle, how can we judge the herd size in GHG terms if the beef:dairy ratio changes through time?

    • Below, this blogpost outlines a straightforward calculation based on emission totals by animal type and the ratio of dairy to beef per head annual methane, based on animal numbers and per head methane emissions given in the EPA National Inventory Report 2020.

  3. What “stable herd” target level might be consistent with societal pathways aligned with Ireland’s ‘fair share’ of a carbon budget for Paris Agreement’s temperature targets?

    • In a recently published EPA Report, Barry McMullin and I looked at the trade-offs between carbon dioxide (CO2) and non-CO2 GHGs for Ireland in society-wide scenarios for effective climate change mitigation (McMullin and Price, 2020). The report’s indicative scenarios make it clear that substantial reductions in methane, 93% from agriculture, are essential to limiting overshoot of Ireland’s all-GHG carbon budget (in addition to the primary climate action focus on reducing fossil fuel usage rapidly to cut CO2 emissions). From this top-down carbon budget basis, it is apparent that a target “stable herd” would need to be much smaller than it is currently – as much as 50% reduction by 2050.

Adjusting herd size for dairy vs. beef differences is essential

Over time, the total numbers and inputs for beef animals and dairy cows are very different and the dairy to beef numbers ratio changes over time. Therefore, the total herd number (simply adding up all cattle including beef and dairy animals), or citing changes in this total, does not provide meaningful information to guide decision-makers in limiting cattle-related GHG emissions. A different measure is needed.

Using the 2020 National Inventory Report data (EPA, 2020a, Annex 3.3), Table 1 shows derived total methane emissions and numbers for all cattle, and sub-totals for dairy and beef cattle, for the 2005–2018 period. Dairy cattle methane increased by 45% and Other cattle methane decreased by 3%, resulting in an overall increase in cattle methane of 11% (46ktCH4/yr) from 418 ktCH4 in 2005 to 463 ktCH4 in 2018.

Table 1. Methane emissions for dairy and beef cattle based on 2020 NIR figures. This table will need to be updated based on revised data for the 2021 NIR that will significantly change the total methane emission and per head intensity values.

2018 ktCH4


2018 ktCH4/


Change ktCH4

% change

2005 number

2018  number

2005 kgCH4





Dairy Cattle









Other Cattle 









Total Cattle







As shown in Table 1, dividing total methane by the number of animals gives the average annual per head methane intensity: for 2005 and 2018, for dairy, 121.6 rising nearly 4% to 126.5 kgCH4/head; for beef, 49.4 falling 1.6% to 48.6 kgCH4/head. As shown graphically in Figure 1, this means that a dairy cow emits 2.6 times the average methane emissions of other cattle (beef cattle including sucklers, with dairy heifers). 

Chart, bar chart  Description automatically generated

Figure 1. As of 2018, dairy cows have 2.6 times the annual methane emissions of beef cattle.

In other words, if further dairy expansion is to occur from 2018 onward then every addition of 10 dairy cows would equate to a reduction in the beef herd of 26 beef animals to prevent a rise in methane emissions. Relative to 2018, the 2027 Sectoral Roadmap: Dairy (Teagasc, 2020) targets an additional 225,000 cows, with 40,000 already added in 2019. 

These values reflect the 2020 NIR, but toward the 2021 NIR the EPA has undertaken a significant recalculation of annual per head cattle methane emissions and excreted nitrogen data as shown in presentation of provisional 2019 emissions (EPA, 2020b), based on updated research (O’Brien and Shalloo, 2019). The provisional data for agriculture, resulting in 2018 total sectoral emissions rising by over 1 MtCO2eq will be finalised for submission by 15 March 2021. Once the 2021 NIR data is updated this blogpost will be revised and a Working Paper will set out the issues raised here in more detail.

Table 2. Reduction in Other cattle required to stabilise cattle methane emissions due to increased dairy cow numbers targeted by the Teagasc 2027 Sectoral Roadmap Dairy, relative to 2018 and 2005.


Relative to 2018 methane emissions

Relative to 2005 methane emissions

Rise in dairy cattle Teagasc roadmap

Rise in CH4 due to higher dairy cattle numbers (in ktCH4/yr)

Corresponding reduction in Other cattle

Rise in dairy cattle Teagasc roadmap

Rise in agri CH4 relative to 2005 (in ktCH4/yr)

Corresponding reduction in Other cattle








By 2027








Teagasc (2017) have stated that stabilising methane emissions is particularly important. If so then beef cattle numbers must fall by the number of added dairy cows multiplied by the dairy to beef ratio of per head annual emissions:

·       Relative to 2018, stabilising methane based on the Teagasc roadmap dairy cow numbers would require a reduction in Other cattle of 104,000 in 2019 and 585,000 by 2027.

·       Relative to 2005, stabilising methane based on the roadmap numbers would require a reduction in Other cattle of 585,179 in 2019 and 1,525,506 by 2027.

Equivalent reductions in Other cattle would be greater than these values if annual per head emissions continue to increase for dairy cows and decrease for beef cattle. Total dairy methane is rising more quickly than total cow numbers because annual methane (and milk) per head is rising. Therefore, total dairy methane emissions are more linearly related to total milk production than to dairy cow numbers.

Coherent agricultural and climate policy requires both dairy and beef numbers based on a clearly stated climate action target

If policy-relevant statements regarding 'stable herd' cattle numbers are to be coherent with climate mitigation policy then the reference year, the climate target (stabilising methane or reducing by an amount and date) and the target rationale (EU or Paris-aligned or other) need to be clearly specified. On this basis alternative corresponding dairy and beef numbers to stay within a stable or declining methane limit can be calculated using the annual per head emission data. Adopting such a straightforward approach to coherent agricultural and climate policy would ease carbon budgeting analysis in assessing alternative transition pathways for agriculture and society.  

The calculations above do not imply that any recent-basis estimates of stable cattle numbers, adjusted for methane or not, are aligned with Ireland’s fair share in meeting the Paris Agreement targets. Our recent EPA Report, including preliminary societal mitigation pathways to meet a Paris aligned carbon budget indicates that substantial and sustained reductions in ruminant production level are required to avoid very substantial overshoot of Ireland’s all-GHG carbon budget. Policy-relevant statements could also reflect this understanding.

As noted above, this blogpost is only preliminary. Once the 2021 NIR data is updated this blogpost will be revised and a Working Paper will set out the issues raised here in more detail.


CCAC, 2019. Annual Review 2019 (Annual report). Climate Change Advisory Council [Ireland].

EPA, 2020a. IRELAND NATIONAL INVENTORY REPORT 2020. Environmental Protection Agency (Ireland).

EPA, 2020b. EPA’s James Murphy presents “Improvements to the Agriculture Inventory.”

McMullin, B., Price, P., 2020. Synthesis of Literature and Preliminary Modelling Relevant to Society-wide Scenarios for Effective Climate Change Mitigation in Ireland  2016-CCRP-MS.36 (EPA Research Report No. 352). Environmental Protection Agency.

O’Brien, D., Shalloo, L., 2019. A Review of Livestock Methane Emission Factors (Research report No. 288), EPA Research. Teagasc.

Teagasc, 2020. 2027 SECTORAL ROAD MAP: DAIRY.

Teagasc, 2017. 2017 - Reducing Greenhouse Gas Emissions from Agriculture - Teagasc | Agriculture and Food Development Authority.