Denmark’s Requirement for Farmers to Feed Cows Bovaer to Reduce Enteric Methane Emissions Has Led to Accusations of Sick Cows and Drops in Milk Production

     There are products on the market that reduce the amount of methane cows produce via enteric fermentation in their stomachs. It has long been known that these products typically reduce milk production.

     Since Late 2025, when Denmark implemented a new requirement for all farmers with more than 50 cows to feed them the supplement Bovaer at least 80 days per year to reduce methane output, farmers all over the country have complained that their cows were experiencing fever, infections, diarrhea, falling milk production, and even death. The UK is set for a similar trial of the supplement, which has been tested extensively in both countries and in the EU.

“The active substance 3-NOP inhibits an enzyme process in the cow’s digestion and can thus reduce methane emissions by up to 30 percent. The supplement has previously been highlighted by chains such as Tesco, Aldi, and Morrisons as a tool to achieve significant emission reductions in milk production.”

     One farmer claimed that when the product was used, the negative health effects appeared, and when it was discontinued, the effects stopped.

“We had to stop giving Bovaer because the cows and our milk production suffered. Since we stopped… the cows showed clear signs of improvement. Two days later, the somatic cell count fell by more than 20 percent.”

     Under threat of hefty fines for non-compliance, it is estimated that 1400 out of Denmark’s 2000 qualifying dairy farmers began administering the supplement. The requirement went into effect one year ago on October 1, 2025. There were hundreds of complaints about sick cows, and many farmers stopped using the supplement. Ida Storm from the Danish Agriculture & Food Council noted:

“We are aware of some cases where dairy farmers report problems after starting to use Bovaer. This is of course of great concern to us.”

     Denmark’s Minister of Food and Agriculture, Jacob Jensen, noted:

“Some farmers are currently reporting challenges in connection with the use of Bovaer. I take this very seriously, and the Danish Veterinary and Food Administration is closely monitoring the situation.”

     A spokesperson for the manufacturer of Bovaer, dsm-firmenish, noted:

“Bovaer has undergone extensive scientific evaluation, with over 15 years of research and no evidence of negative health effects in cows.”

     Some farmers are skeptical that humans can adequately control the complicated biological process of cow digestion. Investigations are underway. Regulators and the manufacturer are baffled that the extensive testing did not reveal potential negative effects, so they are skeptical of the farmer’s claims. The manufacturer claims that Bovaer had been administered to 500,000 dairy cows in more than 25 countries. Below, the company explains how Bovaer works and how it is metabolized by cows. 

     An article in Aeon Magazine explains how cow digestion and Bovaer work and summarizes the testing history.

“Cows digest food in a four-chamber stomach, and during this process, an enzyme in one of the chambers, called the rumen, produces methane.”

“Bovaer, created by a Dutch-Swiss company called dsm-firmenich, contains an active ingredient which suppresses the enzyme that produces methane in the cow’s rumen. According to the company, more than 110 peer-reviewed studies — many of which received funding from dsm or were co-authored by members of its staff —have confirmed the additive’s safety and efficacy in reducing methane emissions from dairy cows by as much as 33 percent. Although some researchers have found that Bovaer reduces feed intake and milk production in cows, none have reported negative health impacts. A statement from Aarhus University, which conducted several studies, summarizes the findings succinctly: The results consistently “showed the desired methane-reducing effect without any signs of disease in the animals.”

     About six weeks after feeding Bovaer was required, there were digestive and metabolic disorders reported by 410 of the 644 farmers who responded to a survey, as well as 434 who noted a decline in milk production. According to Aeon Magazine:

“One possible explanation is that the problems stem from something besides the Bovaer itself. The SEGES report has found that many farmers started their Bovaer use when they made their annual switch to new corn silage. According to Dijkstra, if unstabilized, the silage is at risk of developing unwanted bacteria like clostridia. “I’m not saying that that’s a true problem,” he said. “But we need to distinguish a possible effect of Bovaer as such, with possible other things that happen on the farm.”

     Others think it could be dietary interactions as well, although the product has been tested with multiple forage types and combinations.

     The Danish government began last November to allow affected farmers to temporarily opt out of the requirement. Organic farmers are exempted and could simply feed the cows a higher-fat diet as an alternative – but I am not sure how that equates, maybe less emissions from fertilizers used for the forage crops. Regulators do note that there are some farmers who are not reporting any problems.

“For its part, dsm-firmenich said it is continuing to roll out Bovaer in the 70 countries where it has been approved, including the United States. In an emailed statement, Elanco Animal Health Inc., which distributes the additive there, noted: “Through the end of 2025, our farmer retention rate was over 90%. Elanco has not seen the types of issues that are being reported in Denmark in the more than 150,000 U.S. lactating dairy cows being fed Bovaer since its launch.” And while dsm-firmenich said it is working with Danish authorities to ascertain the origins of the incidents, it also asserted in a written statement to Undark that “there remains absolutely no evidence that Bovaer is a cause of any problems.”

     One farmer, Dr. Anders Ring, who is also a veterinarian, noted that hoof infections from digital dermatitis increased a few weeks after he began feeding Bovaer and stopped when he discontinued. Then, when he started feeding it again at a halved amount, they increased again.

     Earlier this month, dsm-firmenich published an article with data from five dairy farms in Denmark showing no ill effects from the feed supplement. They note that the data:

“…provide insight into how Bovaer® was incorporated into everyday farm routines, what farmers observed and why many chose to continue using it after gaining experience with the product themselves.”

     Data from the five farms in the study showed no ill effects to cows and improved confidence in the product over time. It makes me wonder how much of the reporting of sick cows was anecdotal rhetoric. I’m not saying that is what occurred but asking whether it is responsible for a percentage of cases, and if so, how many.

     The company notes that it has convened a rapid response network of veterinarians and cow nutrition experts to support farmers who may have issues with Bovaer.

“Together with VetSalus, dsm-firmenich has established a Rapid Response Team of veterinary and nutrition experts to support farmers and herd veterinarians when questions arise. Farmers are encouraged to contact their herd veterinarian first, who can involve the team when additional expertise or further investigation is needed.”

 

References:

 

In Denmark, Sick Cows and a Lot of Questions: Farmers blame a food additive required by the Danish government to cut methane emissions, but the source is unclear. Lisa Abend. Undark Magazine. January 5, 2026. In Denmark, Sick Cows and a Lot of Questions

Danish farmers sound the alarm: “Climate feed makes our cows sick.” Samnyitt. November 22, 2025. Danish farmers sound the alarm: "Climate feed makes our cows sick" - Samnytt News

Bovaer affected every herd in Denmark using new feed additive, veterinarian says. Patrick Meagher. Farmer’s Forum. January 29, 2026. Bovaer affected every herd in Denmark using new feed additive, veterinarian says | FarmersForum.com

Methane Inhibitors - Bovaer®. Dsm-firmenich. Methane Inhibitors - Bovaer®

Bovaer® in Denmark: Lessons from five representative dairy farms. Dsm-firmenich. September 23, 2026. Bovaer® in Denmark: Lessons from five representative dairy farms