Methane is the second largest contributor to climate warming after carbon dioxide, which is why scientists have focused a lot of attention on tackling one of the most important sources: methane emissions from livestock. In other words, cow burping and flatulence are bad for the planet.
Farmers add various seaweeds to cows’ diets as a source of protein, unsaturated fats and other health-promoting ingredients that provide immediate energy, says Dipti Pitta of the University of Pennsylvania School of Veterinary Medicine, and a 2016 study in Australia found that it feeding sheep a type of red seaweed Asparagopsis taxiformis (AT) has eliminated methane emissions by 80%.
But the effects of this seaweed vary widely, so researchers from Pitta’s Agricultural Systems and Mbiotic Genomics Laboratory (ASMG lab) and Pennsylvania State University investigated how it changes the microbiome in the rumen, a compartment of a cow’s stomach . The results are published in the journal mBio.
The researchers randomly divided twenty cows into four treatments: a high dose of AT; a low dose of this red seaweed; oregano, which also inhibits methane formation; and the control group. They alternated the animals between treatments in four 28-day periods. The team found that the high dose of seaweed inhibited methane emissions by 55% in the first two periods, but the effect appears to be short-lived. It gradually declined in the third and fourth periods.
Pitta says this is one of the first studies to examine how methane is formed in the rumen and how methane pathways are altered under different mitigation strategies, noting the importance of maintaining microbiome health and animal productivity in tackling methane reduction. Previous research has not examined the effects of AT on microbial populations and their functional pathways at this level of detail.
The researchers found that the high dose of seaweed in the first two 28-day periods led to an almost total elimination of Methanosphaera, a microbe that uses hydrogen to reduce methanol to methane in the rumen. Pitta says this is important because the seaweed treatment did not have the same effect on other microbes that produce methane, leading researchers to believe that Methanosphaera plays a larger role in methane formation than previously thought.
However, the study explains that Methanosphaera Populations increased in later periods because they were unable to inactivate bromoform, a substance in seaweed that suppresses the formation of methane in the rumen.
The study also examined the activity of enzymes involved in methanogenesis, the process of producing methane as a byproduct of energy metabolism. First author Nagaraju Indugu, a senior researcher in the ASMG laboratory, says that the enzymes involved in this pathway were reduced, compared to the control group, when the cows were given AT.
The authors also note that although they expected indirect effects of AT on bacteria in the microbiota, they also found direct effects that were less expected. In particular, the types of bacteria that produce butyrate, a short-chain fatty acid that serves as an energy source for cows, were significantly increased in seaweed-treated animals compared to the control group.
“It is very important to understand what the nutritional value of seaweed is and what the antimicrobial effects of seaweed are so that we can better understand the impact of the overall inclusion of different concentrations of seaweed in the animal diet,” says Pitta.
Indugu says the ASMG lab’s previous work led to the current research. Researchers previously reported that the organic compound 3-Nitrooxypropanol reduced methane emissions by 26%, and a subsequent study determined the microbial characteristics of cows with low methane emissions.
Looking ahead, Pitta says the lab is working on combining different strategies, such as testing seaweed in the diets of cows that have been found to emit high or low levels of methane. “Combining that with the seaweed could give us an opportunity to effectively reduce methane by a much greater magnitude than if you just followed one strategy,” she says.
Pitta adds that researchers are also investigating different doses of seaweed varieties in methanogenic cultures, which will provide more specificity about the concentrations needed to inhibit methanogenesis.
Dipti Pitta is the Mark Whittier and Lila Griswold Allam Associate Professor of Ruminant Nutrition at the University of Pennsylvania School of Veterinary Medicine.
Nagaraju Indugu is a senior researcher in bioinformatics at Penn Vet’s Agricultural Systems and Mbiotic Genomics Laboratory.
The other co-authors are Joseph S. Bender, Grace Dai, Satvik Garapati, Meagan L. Hennessy, Kapil Narayan, Reeti Shah and Bonnie Vecchiarelli of Penn Vet; Camila Lage, Audino Melgar and Alexander N. Hristov, Susanna E. Räisänen, Hannah A. Stefenoni, Sergio A. Welchez and Derek Wasson from Penn State University; and Charles Yarish of the University of Connecticut.
This research was supported by the U.S. Department of Agriculture, National Institute of Food and Agriculture Federal Appropriations (PEN 04538, 1000803, and 2017-05832).
