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June 25, 2019

US researchers question supplementing cattle feed with seaweed as way to fight climate change


Supplementing cattle feed with seaweed may not a realistic strategy to help limit the impact of climate change, according to researchers from the Pennsylvania State University, US.

And, this is even though the practice could lead to a big reduction in methane belched by livestock.

"Asparagopsis taxiformis - a red seaweed that grows in the tropics - in short-term studies in lactating dairy cows decreased methane emission by 80% and had no effect on feed intake or milk yield, when fed at up to 0.5% of feed dry-matter intake," said Alexander Hristov, distinguished professor of dairy nutrition.

However, the scale of producing seaweed feed supplement would have to be immense in order to make it a viable option globally, Hristov added. Furthermore, harvesting enough wild seaweed for the feed of close to 1.5 billion head of cattle worldwide would not be possible.

"To be used as a feed additive on a large scale, the seaweed would have to be cultivated in aquaculture operations," Hristov said. But the harvesting of wild seaweed, he noted, would "deplete the oceans and cause an ecological problem."

Still, the capability of Asparagopsis taxiformis to mitigate enteric methane as a feed supplement demands attention, said Hannah Stefenoni, a graduate student working with Hristov on the research project.

The findings of the research were published recently online in the Proceedings of the 2019 American Dairy Science Association Meeting.

While the use of Asparagopsis taxiformis seaweed to fight climate change would be effective in the short term, the researchers are uncertain about its long term application.

"The microbes in cows' rumens can adapt to a lot of things. There is a long history of feed additives that the microbes adapt to and effectiveness disappears. Whether it is with beef or dairy cows, long-term studies are needed to see if compounds in the seaweed continue to disrupt the microbes' ability to make methane," Hristov explained.

There are also questions about the stability over time of the active ingredients - bromoforms - in the seaweed. These compounds are sensitive to heat and sunlight and may lose their methane-mitigating activity with processing and storage, Hristov warned.

In addition, cows do not seem to like the taste of seaweed. When Asparagopsis was included at 0.75% of the diet, researchers observed a drop in the feed intake by the animals.

The long-term effects of seaweed on animal health and reproduction and its effects on milk and meat quality need to be determined. A panel judging milk taste is part of ongoing research, Hristov said.

Cows burping methane and contributing to climate change has been the subject of considerable derision within the US, conceded Hristov, who is recognised as an international leader in conducting research assessing greenhouse gas emissions from animal agriculture. It is taken seriously in other countries, he explained, as the average dairy cow belches 380 pounds of the potent greenhouse gas a year.

"But methane from animal agriculture is just 5% of the total greenhouse gases produced in the United States - much, much more comes from the energy and transportation sectors," Hristov said.

"So, I think it's a fine line with the politics surrounding this subject. Do we want to look at this? I definitely think that we should, and if there is a way that we can reduce emissions without affecting profitability on the farm, we should pursue it."

And there may be a hidden benefit.

"It is pretty much a given that if enteric methane emissions are decreased, there likely will be an increase in the efficiency of animal production," said Hristov.

Seaweed used in the Penn State research was harvested from the Atlantic Ocean in the Azores and shipped frozen from Portugal. It was freeze-dried and ground by the researchers. Freeze drying and grinding four tonnes of seaweed for the research was "a huge undertaking," Hristov commented.

The research was funded by the USDA's National Institute of Food and Agriculture and the Jeremy and Hannelore Grantham Environmental Trust.

- Penn State News

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