NARO publishes manual on cow methane emissions ― Development of new calculation equation

On June 9, Deputy Leader Tomoyuki Suzuki and his colleagues from the Dairy Cattle Nutrition and Breeding Group, Division of Dairy Cattle Feeding and Breeding Research, Institute of Livestock and Grassland Science, National Agriculture and Food Research Organization (NARO), working with members of Hiroshima University, the National Livestock Breeding Center Tottori Station, Gunma Prefectural Livestock Experiment Station and Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, announced that they have developed a new calculation equation for the sniffer method that is simpler than previous techniques; this equation obtains methane emissions from cow eructation from the methane/carbon dioxide concentration ratio in the breath. They have confirmed it is possible to estimate the methane emissions from different breeds of dairy and beef cow reared in Japan with great accuracy. They have also ascertained that it is possible to evaluate the differences in methane emissions according to feed. The climate change mitigation consortium represented by NARO has published a methane estimation manual on the NARO website, which includes the group's research results. It is hoped that this will accelerate the development of technology to reduce methane emissions from cows.

Cows have four stomachs, and the contents go back and forth between the first and second of these. Together these are known as the reticulorumen. The feed that has been eaten is broken down in the rumen by a great variety of living microbes, and gases such as methane and carbon dioxide (greenhouse gases) are emitted together during eructation.

It has been estimated that 2 billion tons (CO₂ equivalent) of methane created from fermentation in the alimentary canals of ruminant livestock, including cows, is emitted each year around the world, and it is thought that this accounts for 16% of the greenhouse gases emitted by the global farming, forestry and fishery field (approx. 4%-5%).

The Ministry of Agriculture, Forestry and Fisheries' Strategy for Sustainable Food Systems, MeaDRI aims for zero carbon dioxide emissions in agriculture, forestry and fisheries by 2050, and this includes a need to develop technologies to reduce methane from cow eructation.

On the other hand, past measurements of methane emissions from cows have been limited to a standard method that uses a dedicated chamber. This technique measures the total amount of methane emitted from each cow; it is highly accurate, but building and maintaining the system is costly, and in Japan only NARO possess the required facilities. Moreover, it takes around one week to measure one cow, making it difficult to introduce this into a regular breeding facility.

With this background in mind, the research group has focused on developing a calculation equation that is easier to use, connected with the sniffer method that was developed and put into practice in Europe around a decade ago.

The sniffer method was developed using gas leak detection techniques. It estimates methane emissions from the methane/carbon dioxide concentration ratio in the breath, the milk production output, and other sources by collecting a portion of the daily exhalations of a cow. It makes use of equipment such as portable gas analyzers, allowing researchers to measure 50-60 cows in one test, and can be widely introduced as it is easy to install. Specifically, in the case of dairy cows, users install a suction pump near the feed bin of a milking robot and can then individually identify and measure the breath of the cows that come to be milked (2-4 times a day for each cow; around 6 minutes each time).

The new calculation equation was developed by analyzing data connected to the sniffer method, based on the measured values of the methane from 121 cows; this was measured using the standard method and the data was stored by NARO. The equation is as follows.

CH₄ (liters per day) = 5029 × CH₄/CO₂ + 0.536 × body weight (kilograms) + 8.76 × energy-corrected milk yield (kilograms per day) ― 507

The researchers evaluated the accuracy of this, using the standard method as well as the conventional equation and the development equation based on the sniffer method on 18 cows. When they did so, the development equation replicated the numbers of the standard method with high accuracy. The group were able to confirm that its accuracy is at least equal to that of the conventional equation.

They also investigated whether the development equation can be used to evaluate feed. Generally, methane emissions increase when there is a lot of fiber in the feed, and the group tested whether the development equation reflected this. The results showed that methane emissions increased when there was more fiber, the same as the standard method.

The development equation was developed based on data from cows reared in Japan; it is easier to use, and enables researchers to estimate methane emissions very accurately, without needing the number of days after pregnancy - a variable that had been hard to grasp. When it comes to beef cows, the calculation equation was developed in a similar way; it uses the gases collected at feed boxes attached to doors (door feeders), which can identify individual cows, and its accuracy was confirmed. In Japan, researchers are confirming that it is possible to estimate the methane emissions from the commonly reared dairy cows (Holstein) and beef cows (Holstein, crossbreeds, Japanese Black).

The research group have summarized and published their results in the 'Manual for Estimating Methane Emissions from Fermentation in Cow Rumen', a manual on measuring methane from a large number of cows. The manual covers the equipment needed to measure methane emissions, the installation method and points to note when measuring, as well as information about the possibility of improved breeding for cows with low methane emissions. It is hoped that increasing the number of institutions introducing methane measuring will accelerate the development of technology for low methane emissions.

Deputy Leader Suzuki commented, 'Using the feeder method and the development equation will dramatically increase the number of cows that can be measured when compared to the previous standard method, so first we want to go ahead with technological development to ensure a low-methane cow breed. So far, our analysis has been carried out on a limited number of cows, but through the Ministry of Agriculture, Forestry and Fisheries' project, we have learned that methane emissions are hereditary. In the future, we will increase the number of cows and quantitatively determine the extent to which this is hereditary, which we hope will lead to a breeding program based on this data. More specifically, we want to cooperate with research institutions and universities in different prefectures to measure over 1,000 cows over five years and obtain the data we need for breeding, such as individual differences and heritability. We will also explore the possibility of using this to evaluate supplementary development for methane reduction. If this is possible, we hope it will enable us to test different ideas at various research institutions.'