Australian wallaby may hold key to cutting methane emissions

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The discovery that a bacterial species in the Australian Tammar wallaby gut is responsible for keeping the animal’s methane emissions relatively low suggests a potential new strategy may exist to try to reduce methane emissions from livestock, according to a new study.

Globally, livestock are the largest source of methane from human-related activities, and are the third-largest source of this greenhouse gas in the United States, according to the U.S. Environmental Protection Agency.

Wallabies and other marsupials — mammals like the kangaroo that develop their offspring in a pouch — are dependent on microbes to support their digestive system, similar to livestock such as cows, sheep and goats, but Tammar wallabies are known to release about 80 percent less methane gas per unit of digestible energy intake than do livestock animals.

Scientists have used DNA sequence data to devise a way to isolate and grow cultures of a dominant bacterial species from the Tammar wallaby gut and test its characteristics. The analysis confirmed that this bacterium would contribute to a digestion process that produces low levels of methane. Using this information, scientists hope to devise a way to augment the microbial mix in livestock animals’ digestive systems and therefore reduce their methane emissions.

An added bonus for the wallabies, the researchers say, is that the presence of this bacterium frees up more digestible energy for nutritional purposes in host animals. The energy the fermentation process uses to produce methane gas during digestion actually robs animals of some of the nutritional quality of their food.

“Our long-term goals are really to improve nutrient retention by livestock, and reducing methane emissions is just one area where we seek to have a positive impact, both on animal productivity and the environment,” said Mark Morrison, senior author of the study and a professor of animal sciences at Ohio State University. Morrison has an appointment with the Ohio Agricultural Research and Development Center (OARDC) and is also the science leader in metagenomics for CSIRO (Commonwealth Scientific & Industrial Research Organization) Division of Livestock Industries based in Brisbane, Australia.

The study is in press in the journal Science and appeared online as a Science Express report on Thursday this past week. 

Marsupials are often considered similar to ruminants -- a class of mammals that have multiple compartments, including one called a rumen, in their stomachs -- because both groups have a digestive system that supports a “pre-digestion” of food by microbes, to process their plant-based diets. And this process, which includes a period of fermentation to break down the foods and release nutrients, causes the animals to discharge methane gas.

Early research in this area showed that methane emissions from Tammar wallabies amount to 1 to 2 percent of their digestible energy intake, compared to methane emissions of roughly 10 percent of digestible energy intake in sheep. In addition, marsupial and ruminant gut anatomies differ, which influences how quickly food moves through the digestive system.

Over time, however, researchers have noted that Tammar wallabies in particular produce only about a fifth of the amount of methane produced by livestock ruminants as a result of differences in anatomy and microbial compositions in their guts.

Last year, Morrison and colleagues reported that there were key bacterial and enzyme-based differences between the gut contents of Tammar wallabies and other herbivores, including cows.

OARDC is the research arm of Ohio State's College of Food, Agricultural, and Environmental Sciences.



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