The second instalment of the Teagasc beef conference on Wednesday 8 December included a presentation on the implications of slaughter age of beef cattle on greenhouse gas (GHG) emissions from Paul Crosson, beef enterprise leader at Teagasc Grange.

From the outset, Crosson outlined the positive story Irish beef had to tell with one of the lowest beef carbon footprints in Europe and indeed across the world at around 20kgCO2 e/kg beef.

This figure comes from the carbon emissions of both the cow (to produce the calf) and then that animal throughout its production system.

However, there are clear areas that can be improved within the system to decrease overall GHG emissions further in the future.

Such areas include reducing the age at first calving to 24 months, increasing the number of calves weaned per 100 cows to the bull and selectively breeding for lower methane producing animals.

All of these measures are inefficiencies within the system that, if improved on, work hand in hand with productive livestock systems and make both economic and environmental sense.

Reduced slaughter age

Reducing slaughter age also has the potential to reduce the overall GHG emissions from beef systems.

Crosson outlined that a typical beef system in Ireland, at an average slaughter age of 28 months old, has a total GHG emissions (kgCO2e/head) figure of just over 7 tonnes.

If we were to reduce slaughter age by one month, it would potentially reduce the total GHG emissions by around 250kg/head – a reduction of somewhere around 3.6% per animal.

While this may sound like a small decrease on a per-head basis, when calculated across the entire beef industry, across the 1.5m prime animals slaughtered each year, it equates to a direct reduction of 0.2Mt (megatons) to 0.3Mt GHG emissions for each month reduction in slaughter age.

Added to this are reductions from indirect emissions due to a reduced production system length.

These include reductions in soil emissions and emissions associated with purchasing fertiliser and when added together, increases the overall benefit to between 0.3Mt and 0.5Mt GHG emissions for each month reduction in slaughter age.

Grass-based diets

However, research carried out at Teagasc Grange, looking at GHG emissions from various production systems, has shown that if a reduced slaughter age is achieved due to increased levels of concentrate input, there are no benefits in terms of GHG emissions per kilo of beef.

In fact, when comparing a 24-month system where cattle are slaughtered out of the shed in spring on a diet of silage plus concentrate (GC24 in Figure 1), versus a 28-month system off grass where no concentrate is fed (GO28 in Figure 1), the GHG emissions/kg beef are lower in the 28-month system.

This is due to the higher GHG emissions associated with concentrate feed compared to grass.

Figure 1 outlines the four production systems that were compared, all of which used continental-bred steers.

The system profiled that had the lowest GHG emissions/kg beef (red line on graph) was where animals were slaughtered off grass at the end of the second grazing season from a grass-only diet (GO20).

However, there were issues over hitting carcase specification in this system in terms of carcase fat score.


Reducing the slaughter age of beef cattle has the potential to reduce total GHG emissions from the system, but as this study indicates, diet is just as important a factor.

GHG emissions per kilo of beef should be the main focus as a per-head basis can mask the true figure.

There are two key components to the GHG emissions per kilo of beef – age at slaughter and carcase weight.

A heavier carcase weight means there are more kilos of beef to divide the emissions over.

It is for this reason that under 16-month bull beef systems, despite having a higher concentrate input, come out favourably in terms of GHG emissions per kilo of meat.

Recent research has backed this point up once again and, in the coming weeks, the Irish Farmers Journal will explore these numbers further.

Ireland is a predominantly steer-producing country due to our reliance on the UK market. We are told that UK consumers want steer beef.

However, in a time where consumers are becoming more aware of the carbon footprint of their diet, would a lower GHG emissions alternative, if marketed as such, not be welcomed?