Since early October, when the use of the Bovaer additive became mandatory for herds of 50 or more cows in Denmark, Danish farmers have reported cases of fever, diarrhea, reduced fertility and even deaths among their herds.

Norway decided to freeze its use of Bovaer pending further investigation, said Norsk Melkeravare, which supplies milk from farmers to Norway's biggest dairy cooperative Tine.

"No negative effects from the use of Bovaer in Norway has been reported at this point," company head Johnny Odegard said in a statement.

"As a precaution, Norsk Melkeravare ... has nonetheless decided to implement a pause while we get more information," he said.

Made by the Swiss-Dutch conglomerate DSM-Firmenich and approved by the European Food Safety Authority (EFSA), Bovaer reduces climate-harming methane emissions from cows by 20 to 45 percent.

According to EFSA, milk from cows that have ingested Bovaer is safe for human consumption, with no trace of the molecule found in their milk.

Livestock farming as a whole -- from the production of feed and fertilisers to the animals' rumination -- is responsible for about 12 percent of human-caused greenhouse gas emissions.

This is largely due to methane emissions, which are released during the digestion process of ruminants when they belch.

Methane is the second-largest greenhouse gas after carbon dioxide.

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DSM-Firmenich