Burps and breath from cows and other farm ruminants are strong contributors to climate change. Researchers from Aarhus University have found that breeders can target methane emissions on two fronts. 

Ruminants such as cows produce the potent greenhouse gas methane as a natural by-product of feed fermentation in the rumen. There are efforts in the agricultural sector to find ways of reducing the emission of methane from ruminants. One of the methods is to select for cows that are genetically pre-disposed to emitting less methane, as cows vary in how much methane they emit. However, more than one path can be taken. 

Researchers from Aarhus University have recently found that two separate factors influence dairy cows’ variation in methane production. One factor is the individual cow genotype while the other is the composition of her rumen microbiome. If breeders can target methane emissions on both these fronts, it could lead to greater advances in lowering methane emissions. 

- Our study demonstrates that variation in methane emission is likely not modulated through cow genetic effects on the rumen microbiome. Therefore, the rumen microbiome and cow genome could be targeted independently, by breeding low methane-emitting cows and, in parallel, by investigating possible strategies that target changes in the rumen microbiome to reduce methane emissions in the cattle industry, the authors state in an article published in PLOS Genetics. 

Samples taken on commercial dairy farms

The researchers had the hypothesis that the relative composition of the microbiome in the rumen is heritable i.e. controlled by host genome, and that variations in rumen methane emission is influenced by both the cow genome and rumen microbial content. They sampled rumen contents of 750 dairy cows on five commercial farms in Denmark. Methane emission from these cows were measured individually during automated machine milking for one week. 

The researchers observed considerable variation in methane emission among the cows. The top 10 percent of methane-emitting cows thus had a 41 percent mean difference from the lowest 10 percent. 

In the rumen samples, the researchers found a wealth of microbes. They identified 3,894 bacteria and 189 archaea (a separate group of single-celled organisms), which were present in a minimum of 50 percent of the cow samples. The relative abundance of some of these microbes is heritable and associated with methane production. However, the majority of variation in the relative abundance of rumen bacteria and archaea is due to non-genetic factors. 

- The cow’s genetics can explain 21 percent of the variation in methane production and the rumen microbes can account for 13 percent. Importantly, the two are largely independent of each other, so breeding for low methane-emitting cows is unlikely to result in unfavourable changes in the rumen microbiome, the authors note. 

Genetics is sustainable

Targeting rumen microbial communities through feed additives, feed formulations, and anti-methanogen vaccines is also possible, but these strategies are not cumulative. Even transplanting rumen bacteria is not a permanent solution as the microbiome returns to its pre-transplantation composition after a short period. In contrast, focusing on the genetics of the cow and of the microbiome can have a more sustainable, persistent, and cumulative over subsequent generations. 

The methane that cows emit also has an energy value and represents a 2-12 percent net loss of the cow’s gross energy intake. Consequently, cattle and other ruminants with increased efficiency to digest high fibre feedstuffs but reduced methane production could in principal benefit the global climate and concurrently improve the profitability and sustainability of cattle production.

The study was carried out in collaboration between Aarhus University, Technical University of Denmark and University of Arizona under the project REMRUM funded by the Danish Council for Strategic Research.

You can read the article Host genetics and the rumen microbiome jointly associate with methane emissions in dairy cows published in PLOS Genetics.

Facts about cows and climate change

• Cows, sheep and other ruminants produce methane in their digestive process.
• Methane (CH4) is a greenhouse gas that is roughly 30 times as heat-trapping as carbon dioxide (CO₂).
• Methane has an atmospheric half-life of 12 years, which is substantially shorter than CO₂ (> 100 years).
• Livestock accounts for 14.5 percent of anthropogenic-related greenhouse gas emissions. Methane emissions from ruminants account for 5.8 percent.
• Approximately 99 percent of methane emitted from cattle is released by burping and breathing.
• Methane emission from livestock is predicted to markedly increase due to an expected doubling in the global milk and meat demand by 2050.

For more information please contact:

Senior researcher Goutam Sahana, Center for Quantitative Genetics and Genome Research , Department of Molecular Biology and Genetics, email: goutam.sahana@mbg.au.dk, telephone: +45 8715 7501