Cow microbiome study - paving the way to lower emission cows
Reducing the amount of methane produced by cows, by looking at the bacteria in their gut
Cattle are an important food source globally. With a rapidly growing human population, an increase in demand for beef and dairy cattle is expected. However, population growth and cattle production both produce greenhouse gasses. Methane is a greenhouse gas with 28 times the warming effect of carbon dioxide. Methane gas produced by cattle is the leading source of human related methane production. Methane production is bad for the farming industry too, cattle that produce more methane need more food and have a higher production cost.
Scientists at The Roslin Institute, along with the Scotland’s Rural College, and The Rowett Institute in Aberdeen, have discovered a link between cattle genetics and methane production, as well as a convenient way to select for bulls that produce less methane. This can be used to improve beef and dairy stock globally.
We employed a relatively new technique called metagenomics, which involves analysing the genetic composition of an entire organism including the microbes that exist within it. Our study demonstrates the power of combining this approach with big data analysis tool to solve a real world problem – in this case breeding more efficient animals.
Where does methane come from?
Cattle are ruminants, they have four stomach compartments that give them the capacity to house microbes that can break down the fibre in grass and give it to the cattle for energy. One of the stomachs, called a rumen acts as a fermentation vat where microbes break down the fibre. It is also these microbes that produces methane, which gets burped out during digestion (this process is called rumination). There are two populations of microbes in the rumen, bacteria and archaea, with both contributing to the grass breakdown process. It is the archaea that produce most of the methane. Having more bacteria compared to archaea can decrease methane production in cattle and improve feed efficiency.
How can we change the microbial population?
Many studies have attempted to reduce methane production in cattle, often focused on changing diet, or vaccinating cows against methanogenic archaea. These techniques have had limited success.
Instead, scientists at The Roslin Institute did a metagenomic analysis, which is a way to look at all of the genes in an animal, including those from the microbes in their gut. This allows us to identify microbes that are expressing specific problematic genes, including some that we cannot detect through traditional methods.
This analysis revealed that there is a genetic component in cattle that influences what microbes can better colonise the rumen. At the same time, methane production from related family groups was compared. Scientists documented which family groups produced the least amount of methane and tied it to the ratio of bacteria: archaea in the gut.
The difference between the extremes in methane production was 88%, meaning that there is a large difference between cattle families with regard to efficiency and methane production.
There are many genes in cattle that influence what microbes survive better, it is easier and just as effective to look right at the microbes and let them guide us in our search for lower emissions cattle.
How can this be used?
Currently, bulls are tested for a number of traits and given a score based on the genes they carry. As their offspring grow and get assessed, more information is added to the score. This determines the bull’s value, and how many times he is used to breed new cattle. Adding information to the score about a better ratio of bacteria: archaea can be used to decrease methane production in future cattle.
Selective breeding is one of the most ancient method of genetic engineering. By using individuals with a desirable trait more often, we increase the number of offspring that have the traits we seek, changing the entire population over time. Moving forward, it seems possible to pair more beef and dairy production with a decrease in methane output, increasing global food security while decreasing our impact on the planet.