COMMENT

Meat and dairy are New Zealand's biggest earners when it comes to exports, however, they are also our largest contributor to greenhouse gas emissions. As we try to balance our economy with our commitment to the Paris climate agreement new research out this week thinks the secret to reducing climate change could be through breeding less burpy cows.

Methane emissions from ruminants including sheep and cows account for about a third of New Zealand's greenhouse gas emissions and are by far the largest single contributor. Although methane stays in the atmosphere for less time than carbon, as a gas it is much more effective at trapping heat - acting as a blanket over our planet and playing a significant role when it comes to climate change.

Methane isn't physically produced by the ruminants themselves, instead, the animals act as a host to a group of microbes called methanogens that live in their digestive system. It is these methanogens that produce the methane by combining hydrogen and carbon dioxide during food digestion. To look at the relationship between methane emissions and livestock, a large European Union commissioned research project called RuminOmics took a team of more than 30 scientists and several breeds of common cow to see if there was a simple way to reduce the amount of methane produced.

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The scientists inserted a brass cylinder into the mouth of the cows they were studying and pulled up fluid from the rumen, the first of four compartments found in the stomach of a cow. This is the area where grass that has been chewed and swallowed by the cow gets partially digested through a fermentation reaction. The researchers found that this fluid contained different types of protozoa, bacteria, fungi, DNA and single-celled organisms known as archaea. The bacteria produce hydrogen as they ferment the carbohydrates from the chewed up grass which is then combined with carbon dioxide by the archaea in the rumen producing a methane-rich gassy combination, 95 per cent of which is burped out by the cow.

Previous research has tried to solve this methane emissions issue by changing the diet that the cows ate, with the addition of seaweed instead of grass as one way of reducing the amount of methane produced. Although the extra seaweed was successful in methane reduction, the additional food cost plus the extra carbon footprint needed to transport seaweed to farms did not make it a viable option for many farmers. Rather than change the diet of the cow, the RuminOmics research, which was summarised in the journal Science Advances, found that it was more effective to change the methane-producing bacteria that lived in the cow. Their results found a strong link between the genetic make-up of the cow and they type of microbe that lived in its digestive system with high methane-producing microbes being inherited from one generation to the next. The simple solution they found was to selectively breed cows that didn't have these inherited genetic traits which seemed to relate to the hosting of high methane-producing microbes. The study agreed with local work carried out at AgResearch, which has also been successful in selectively breeding sheep that have specific genetics to produce less methane from their grassy diets.

Altering the genetic make-up of cows by breeding for good heritable traits is standard in the livestock industry although it has typically been tailored to produce improved milk or meat yields. Now the challenge is to see if both an increased milk or meat yield and lower emissions can be bred together into one single productive yet environmentally friendly and less burpy cow.