Sheep index reduces methane and improves performance

Results from thousands of methane measurements from sheep flocks in Ireland confirmed that genetics play a role in gut fermentation.

This means farmers can opt for lower emissions, reducing greenhouse gas (GHG) emissions and increasing productivity in the process.

See also: 17 Ways Sheep Farmers Can Work Towards Net Zero

That’s according to Nóirín McHugh, senior scientist in Teagasc’s animal and biosciences division.

He is confident that the methane trait will be included in Ireland’s national sheep performance by 2023-24.

“Methane is an inefficiency in the system,” says Dr McHugh. “It’s energy that the animal doesn’t use to turn grass into a product like meat. It is equal to 2-12% loss of feed energy.

“Anything we can do to reduce methane in the animal will also increase efficiency, so it’s a win-win from an operational standpoint.”

Emissions from sheep

Agriculture is Ireland’s largest GHG emitter, responsible for producing just over a third of the country’s total emissions.

This resulted in bad press for the industry on a weekly, even daily basis, he says.

The average sheep produces 11 kg of carbon dioxide (CO2e) equivalent per live weight. This is equivalent to 10% of GHG emissions from agriculture. Of that 11 kg, 7 kg is methane from gut fermentation, he adds.

In addition to taking steps to improve pasture management and maintain soil fertility, breeding strategies such as selecting for faster growth, targeting higher yields and reducing age at first lambing can be used to reduce greenhouse gas emissions.

Currently, Irish sheep farmers can use Sheep Ireland’s Euro-Star terminal and replacement indices to help them select animals of high genetic merit.

Primary research

To determine how this selection process affects farm profitability and greenhouse gas emissions, Dr McHugh and his team used real data from commercial herds to model the two herds (see “Comparison of performance and GHG emissions between one-star and five-star herds”).

A higher weaning rate and fewer days to slaughter accounted for an increase of €18 (£15.68) per ewe in the five-star flock.

The researchers also looked at GHG intensity between the two herds and calculated a 7% reduction in CO2e from the five-star herd.

Comparison of performance and GHG emissions between one-star herds and five-star herds

One star herd

Five star herd

Herd size

257 head sheep

257 head sheep

Territory

20 ha (49 acres)

20 ha (49 acres)

Weaning rate (lambs per ewe)

1.54

1.70

Days to cut

203

190

Productivity improvement (€/ewe) (£/ewe)

+18 (+15.68)

Emissions (CO2e/kg product)

>23

22

Emission reduction (%)

7

Note: The one-star herd represented the lowest 20% genetic merit for replacement-type traits, while the five-star herd used the highest genetic lines.

“This is very good news: index selection is currently improving herd-level productivity, economic performance and greenhouse gas intensity,” says Dr McHugh.

“But in Ireland when we talk about GHGs and targets set by the government, it’s the total GHG emissions of our sector, not GHGs/unit of output. Thus, to reduce total GHG emissions, we must actually select directly for methane emissions.

He explains that this means measuring methane in individual sheep to identify high and low emissions in flocks and ultimately develop breeding values ​​for methane.

Forecasting methane emissions

To do this, Dr McHugh and his team are measuring methane emissions from flocks across Ireland using 12 trailer-mounted portable battery cameras (Pacs).

On each farm, 12 sheep are removed from the feed source one hour before entering the Pacs, where methane, carbon dioxide and oxygen measurements are taken at 0, 25 and 50 minutes.

12 trailer-mounted portable battery cameras (Pacs) © Eoin Dunne

Dr McHugh says this method provides a good predictor of methane emissions and is a very useful way of sorting sheep.

Based on the data collected so far, the team found that a dry sheep would produce 19.29 g of methane per day.

This compares to 240 g/day from a lactating cow and 230 g/day from a final spike.

“Sheep are not the main culprits,” says Dr McHugh. “But in terms of methane/kg live weight, it’s 0.4 to 0.6 g, which is very comparable to a dairy cow or beef.”

Genetic influence

Further research has shown that methane production increases as sheep grow and is highly correlated with feed intake.

However, there is a lot of variation – and this has raised the question of how much of this is genetics and whether animals can be genetically selected to produce less methane for the same level of output.

Based on 12,000 measurements from commercial and breeding herds, the results so far are encouraging: they show that methane has a heritability of 25%.

“That means if you have two animals, 25% of the difference in the methane they produce is due to genetics,” he says.

“It does not depend on the diet, sex or age of the animal; it depends purely on the genetic makeup of the animal. This is comparable to lamb live weights here.

“The other good news is that it’s about 40% reproducible – which tells us that if we measure an animal early in life, we’ll have a good predictor of what methane profile it will have later in life. So it allows us to create an image very quickly.

True breeding values

The goal now is to include the methane feature in the actual breeding values ​​and see the methane values ​​displayed alongside the existing star ratings for the national terminal and replacement indices.

Farmers in Ireland can then use these when selecting rams for the breeding season. The goal is to do this in 2023-24.

Dr McHugh says no breed will solve the problem, and there is also variation between breeds – there is a difference of about 8g of methane per day between the lowest and highest emitters.

“Importantly, we don’t want a sheep that produces low methane but doesn’t tick the boxes for everything.

“Thus, methane is reduced, but at the same time high productivity, high growth rate, good health and so on. We need to correlate it with other production traits to make sure we select animals that have

“So we want to nurture these low emitters in the future, while maintaining our high level of performance.”

A carbon cost sub-index is also considered within the terminal and replacement indices.

This will allow farmers to dig deeper into specific traits, as they already can for the lamb, growth and carcass sub-indices.


Nóirín McHugh was speaking at an AHDB webinar on raising sheep to reduce methane emissions.

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