Measuring methane from sheep systems

To date methane emissions have never been measured from Irish sheep production systems. Teagasc and UCD researchers together aim to develop methods of measuring methane production from sheep and to investigate if sheep can be bred to produce lower methane emissions.

Main Messages

• Methane is a potent gas produced by enteric fermentation in ruminant animals
• Portable accumulation chambers (PAC) can be used to measure methane emissions in pasture based sheep production systems
• The PAC can identify high and low methane emitting sheep in the flock

Introduction

The Irish agricultural industry accounted for 34% of greenhouse gas emissions (GHG) in 2018.  Carbon dioxide, methane and nitrous oxide are the three major GHG’s produced by agriculture. Ruminant animals are the leading source of methane, which is produced through enteric fermentation (i.e. as a product of feed digestion in the rumen). The agricultural sector is under significant pressure to reduce these emissions to reach the countries 2030 target of a 30% reduction in overall emissions. To date methane emissions have never been measured from Irish sheep production systems. Therefore our objectives are to develop methods of measuring methane production from sheep and to investigate if sheep can be bred to produce lower methane emissions.

Measuring methane emissions

Portable accumulation chambers (PAC) allow for methane emissions to be measured from grazing sheep. It is a point in time measurement where methane, oxygen and carbon dioxide measurements are taken from individual sheep at three time points (0 minutes, 25 minutes and 50 minutes) within a 50 minute period. There are 12 PAC in total, with a capacity for 60 sheep to be measured daily. All animals must go through the chambers twice, at least 14 days apart. The PAC are mounted on a trailer which will allow for methane measurements to be taken on commercial farms around the country. Portable accumulation chamber measurements will be combined with genomic data and animal pedigree information to generate large volumes of data from thousands of animals within our national flock. This data will contribute to determining the influence of genetics on methane output in sheep systems. While the PAC measurements differ from absolute values obtained through continuous 24hr measuring, they can be used to rank animals thus identifying high and low methane emitting sheep in the flock. The ultimate aim is to breed sheep with reduced methane emissions without compromising animal performance.

Currently at Teagasc Athenry there is a study following a group of 60 female animals, originally selected as lambs in 2019, from the INZAC flock. The group consists of two breeds, Suffolk and Texel, and can be broken down into Elite Irish, Low Irish and Elite New Zealand genetic groups. In the winter of 2019 these 60, then ewe lambs were involved in a study looking at how the PAC compares to the ‘gold standard’ method of measuring methane using respiration chambers while in 2021 we will also look at comparing PAC measurements to the sulphur hexafluoride (SF₆) tracer technique, this is a method of measuring methane emissions in grazing sheep. The 60 hoggets as well as the remaining ewes in the INZAC flock will be followed throughout their lifetime to look at how methane emissions vary depending on life stage (i.e. lamb, hogget and ewe), stage of production (i.e. dry, pregnant and lactating) and diet type. Throughout the project animals will be measured on various feed types including perennial ryegrass and grass silage. The feed intake and rumen composition of the animals, both at grazing and during winter housing, will be measured allowing the relationship between feed intake, rumen function and methane output to be investigated. Following on from the winter 2019 measurements, during the summer of 2020, approximately 1000 animals from the sheep flocks at Teagasc Athenry have been measured in the PAC.  

Results and Conclusion

In January/February 2020 48 ewe lambs were used to develop a standard operating procedure for the optimum use of the PAC. This study showed that sheep need to be in the PAC for 50 minutes to get a true reflection of their methane output. The ewe lambs produced on average 8.62 CH₄ g/day and 561g CO₂ per day from a grass silage based diet. The study showed that the time and day of measurement, the relative humidity and the live-weight of the animal all impacted the methane output. Following on from this recent results have shown that methane output these same animals measured as dry hoggets was 14.5 CH₄ g/day on a perennial ryegrass based diet. Methane output from mature ewes, weighing on average 80kg live-weight, on a perennial ryegrass based diet ranged from 10-35 CH₄ g/day with an average methane output of 20.5 CH₄ g/day. This range in values obtained shows the large degree of variation in the methane output between animals. In conclusion initial results from this work show that methane output is influenced by many factors including animal live-weight, diet type and the length of time off feed prior to measurement. The variation observed, when taking into account each of the above factors, is potentially due to the genetic make-up of the animal with results showing that elite genetic merit animals have a lower methane output in comparison to low genetic merit animals.

Acknowledgement:

The Researchers:

Edel O’ Connor^1,2, Nóirín McHugh ¹, Tommy Boland ², Eoin Dunne ¹, Fiona  McGovern.^1
1 Teagasc, Animal and Grassland Research and Innovation Centre, Athenry, Co. Galway.
² School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4.

would like to acknowledge the Department of Agriculture, Food and the Marine for funding through the GREENBREED and GrassToGas projects via their stimulus and ERAGAS funding programmes.