The farmers say their cows are suffering from issues including fever and diarrhoea, fertility performance has been impacted, and in some instances farmers have reported cows have collapsed and died.
Bovaer is a feed additive containing the active ingredient 3-nitrooxypropanol (3-NOP), that reduces methane emissions produced by cattle.
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Manufactured by Swiss company dsm-firmenich, it is designed to be added to cow feed in small quantities to inhibit a specific enzyme in the animal's digestive system, which can cut methane production by up to 30% in dairy cows.
Arla hit the headlines last year after it began using the supplements on farm. The dairy giant has now ended the project, with the findings being reviewed. It confirmed that the projects finished when they were planned to and that there was no link between this and the reports in Denmark.
Compulsory
Danish government made the feeding of Bovaer in herds of over 50 cows compulsory on October 1, 2025. On these farms, Bovaer must be added to the cow's ration for at least 80 days a year. Farmers who do not comply could be faced with fines.
There are around 2,000 dairy farmers in Denmark, 1,400 of which are thought to have started feeding Bovaer on October 1, 2025. The Danish Dairy Board is advising farmers to report any issues with the additive.
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Anders Ring, who milks 600 cows near the small town of Gredstedbro on the southern Denmark coast, says he sawa number of problems in his own herd while feeding Bovaer, and has since stopped, noting an overall improvement in cow health after he did.
Mr Ring said: "In my opinion, Bovaer is a poison. Since we started feeding Bovaer, we have had an explosion in digital dermatitis, and many cows [have shown signs of] bad reproduction.
Health checks
"I have also noticed a lot more cows are now on health checks via my computer system, and the cows have also had higher somatic cell counts."
After feeding Bovaer to his cows for a month, and witnessing a fall in the herd's overall health and milk production, Mr Ring said he decided to stop feeding the additive.
He said: "Since we stopped feeding it, cow health showed huge signs of improvement. And two days after we stopped feeding Bovaer, our somatic cell count fell by more than 20%."
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Jacob Jensen, the Danish Minister of Food, Agriculture and Fisheries, said he was aware some farmers were ‘reporting challenges' in connection with the use of Bovaer.
He added: "I of course take this very seriously, and the Danish Veterinary and Food Administration is following the matter closely."
A spokesperson from dsm-firmenich said: "We are deeply committed to safeguarding the health and wellbeing of livestock, supporting farm performance, and securing the future of dairy farming, as we have consistently done for decades.
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"Currently, around 1,400 Danish farmers are using the Bovaer feed supplement, and we are aware that in recent days, some farmers have raised concerns about cow health.
"We are actively engaging with the relevant organisations to ensure that all these concerns are fully investigated and properly addressed.
"In previously reported cases, Bovaer was not identified as a contributing factor to the health concerns raised."
Concern
Ida Storm, director, Danish Agriculture and Food Council for Cattle (DAFC Cattle), said: "We are familiar with some cases where dairy farmers report problems after starting using Bovaer. This is obviously of great concern to us.
"Animal welfare must not be compromised. At the same time we are surprised, since no research or large-scale trials have indicated problems."
She added that DAFC Cattle had launched an online survey where dairy farmers can report problems.
She said: "We hope to quickly learn more and hopefully find solutions. We strongly urge farmers who experience problems to participate."
