Doubts persist after Bovaer study finds no clear impact

A major new Danish study has found no evidence that methane-reducing feed additive Bovaer increases cow mortality or reduces overall milk yield, though researchers say significant uncertainty remains over its effects in some herds.

The analysis by Aarhus University’s National Centre for Food and Agriculture examined data from 73 dairy herds with about 27,650 cows using Bovaer in 2025.

It found no clear link between the additive and increased mortality, disease incidence or reduced milk yields across the dataset.

See also: Bovaer maker defends product after Danish farmer fears

“We cannot see any clear overall impact of Bovaer on either production, disease or mortality in the data we have analysed,” said associate professor Niels Bastian Kristensen, who led the study.

The study was commissioned by the Danish Agency for Food, Agriculture and Fisheries after reports from farmers in late 2025 of dairy cows collapsing, experiencing a drop in milk production and suffering from diarrhoea after the Danish government mandated the use of Bovaer.

Developed by Swiss-Dutch firm DSM-Firmenich, Bovaer is designed to reduce methane emissions from cattle by inhibiting methane formation in the rumen.

It contains 3-nitrooxypropanol (3-NOP) and has been approved for use in the EU following a scientific assessment by the European Food Safety Authority (Efsa), the bloc’s food safety regulator.

It was approved for use in the UK in December 2023 following an assessment by UK regulators, including the Food Standards Agency.

DSM response

Responding to the findings, Jonathan Westlake, Bovaer business development manager at DSM-Firmenich, said the company “welcomes the publication of the National Centre for Food and Agriculture, Aarhus University’s analysis confirming no evidence of any negative effects of the use of Bovaer in Danish dairy herds in 2025”.

However, the researchers also highlighted a more complex picture beneath the headline results.

A separate survey of 644 herds by SEGES Innovation previously suggested about two-thirds reported some form of production or intake decline during Bovaer use.

While the Aarhus analysis found no consistent overall pattern, it acknowledged that some individual herds experienced “serious problems”, with researchers saying outcomes varied significantly between farms.

The researchers added that “unanswered questions” remain.

Prof Kristensen said some farmers described “running into a wall” after introduction, though the data did not show a universal effect.

“We have a number of reports where we have to agree with dairy farmers that what they have experienced has been devastating,” he added.

Methodological questions

The study also raised methodological questions, as it was conducted over a short period of about three months and is based on retrospective data from herds where Bovaer had already been introduced.

Further controlled research is under way, with welfare studies continuing until 2028.

An Efsa call for evidence on real-world Bovaer use is expected to report by the end of June, which could shape future regulatory decisions across Europe.