Data analysis carried out by independent non-profit research organisation SEGES Innovation in Denmark has suggested that Bovaer, in combination with high sulphur content in the feed ration, increases the risk of metabolic disorders in cows.
Research was undertaken after many farmers in Denmark complained of negative results within their herds after feeding the methane-inhibiting feed additive Bovaer to the cows’ diet.
Since January 1, 2025, all conventional dairy farmers in Denmark with more than 50 cows are required to reduce methane emissions by adjusting their feed.
The Danish Dairy Farmers’ Association previously told Agriland that the feed additive had been used in “relatively few herds in the spring, without significant changes in the cows’ appetite or welfare in most cases”.
Around 1,400 herds, out of Denmark’s total of about 2,000, are believed to have started administering Bovaer around October 1 last year.
A spokesperson for dsm-firmenich, the company that developed Bovaer said: “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.”
Sulphur
According to the data analysis by SEGES Innovation, a large proportion of the sulphur content of feed rations comes from rapeseed meal and rapeseed cake.
“There is therefore reason to suspect that the combination of Bovaer and a high proportion of rapeseed products increases the risk of dairy producers experiencing more metabolic disorders in their herd,” the research outlines (translated to english).
Farmers who use rapeseed products exclusively as a protein source, SEGES Innovation recommends that you wait to feed Bovaer until the autumn of 2026, as it is expected that the risk assessment regarding the combination of Bovaer and high sulphur content will be investigated in trials this spring (2026).
Alternatively, farmers are advised that they can consider replacing rapeseed products completely or partially with soy meal.
“It should be emphasised that the data analysis cannot say anything conclusive about causal relationships between Bovaer and the sulphur content in the ration.
“The data analysis is based on a relatively large number of herds and with high statistical probability. Due to a precautionary principle, SEGES has chosen to present the results,” the report outlines.
Analysis
The analysis is based on 200 large breed herds that have indicated that they have not changed feed materials in connection with starting with Bovaer.
Correlations between feed ration parameters and the experience of using Bovaer have been analysed by SEGES Innovation researchers.
92 feed ration parameters have been studied in the form of nutrients, minerals, vitamins, energy, filling and protein values. These have been calculated in the feed assessment system NorFor.
The analysis shows that the sulphur content of the ration is significantly higher (2.62 vs 2.48g/kg DM) in the feeding plans of herds that have indicated an increased incidence of feeding and metabolic disorders.
Rapeseed products
Sulphur is found especially in rapeseed cake and rapeseed meal and typically accounts for 50-60% of the sulphur content in a cow’s feed ration when rapeseed is the primary protein source, according to SEGES Innovation.
In rations with a high corn silage content, 70%+ of the sulphur can come from rapeseed products. Sulphur is found especially in the amino acids cysteine ​​and methionine.
The data analysis combined with symptoms from cows in practice, leads to a hypothesis that Bovaer in combination with high sulphur content may be a direct or contributing cause of the sick cows that dairy farmers have reported.
Bovaer increases the availability of hydrogen in the rumen, while rapeseed products contribute sulphur. The combination of hydrogen and sulphur can lead to the formation of hydrogen sulphide (H2S), which is a toxic gas for cows and humans.
SEGES stated that there is little literature on hydrogen sulphide measurements on cows fed Bovaer and sulphur/rapeseed products, and it is therefore not known for sure whether this is the explanation for some of the incidents observed in some herds.
The risk of feeding Bovaer and rapeseed products is expected to be investigated more thoroughly in trials at Aarhus University (AU) in the spring of 2026.
