3-NOP (3-Nitrooxypropanol, Bovaer) in Animal Feed: Function, Forms, Dosage and Regulatory Status

Bovaer is the trade name of 3-nitrooxypropanol (3-NOP), an EU zootechnical feed additive (identification number 4c1) that reduces enteric methane production in dairy cows. Which cows may receive it, and at what level? EU law allows 3-NOP in feed for dairy cows and cows for reproduction between a legal minimum of 53 and a legal maximum of 80 mg per kg complete feed (12 % moisture).

3-NOP is authorised in the EU until 2032-04-28, while in the US it is an unapproved animal drug marketed under FDA enforcement discretion since 2024-05-24. It is also the only entry in functional group 4c among the feed additive categories of Regulation (EC) No 1831/2003.

This page sets out what 3-NOP is and how it blocks methane formation in the rumen, the inclusion limits and their bases in the EU, GB and the US, the meta-analysis evidence of a 31 to 33 % methane reduction in dairy cows, the dated legal status side by side, EFSA's safety conclusions, stability in premixes and pellets, and a specification checklist for buyers.

The identity table below lists the substance data and the legal anchors of 3-NOP in one place.

What Is Bovaer (3-NOP)?#

Bovaer is a feed preparation that contains at least 10 % 3-nitrooxypropanol, a small synthetic nitrate ester (C3H7NO4, 121.09 g/mol) that inhibits the enzyme rumen archaea use to form methane. The active substance is a mono-constituent substance, also listed as 3-hydroxypropyl nitrate and propan-1,3-diol-mononitrate. Bovaer 10 is the commercial form on record, sold as a 10 % preparation on silicic acid with propylene glycol.

The EU authorises 3-NOP for one function, "reduction of enteric methane production", and the US label claims "reduction of methane gas emissions per pound of dry matter intake".

What is Bovaer made of? 3-NOP, propylene glycol and silica#

Bovaer 10 consists of at least 10 % 3-NOP (typically 10.5 %), 35.2 % propylene glycol and 54.3 % silicic acid, according to the composition EFSA assessed in 2021. In this carrier, propylene glycol is a feed material in its own right, and the silicic acid gives the granules their free-flowing form. The US label states the same minimum of 10 % 3-NOP and caps silicon dioxide at 60 % of the product.

Who holds the Bovaer authorisation, and who sells it?#

The EU holder of 4c1 is dsm-firmenich Switzerland Ltd., represented in the EU by dsm-firmenich Austria GmbH, since Implementing Regulation (EU) 2026/98 of 15 January 2026. That act changed only the holder name; stocks labelled under the earlier name may be used until exhausted.

In North America, Elanco US Inc. distributes Bovaer 10, and Elanco received the FDA letter of 2024-05-24. dsm-firmenich announced on 9 February 2026 the sale of its animal nutrition and health business to CVC, and Bovaer is not part of that sale.

Which EU Category and Functional Group Covers 3-NOP?#

3-NOP belongs to category 4, zootechnical additives, and to functional group 4c, "substances which favourably affect the environment", where 4c1 is the only entry in the EU Register (read 2026-11-03). The authorised function is "reduction of enteric methane production", in force since the authorisation date of 2022-04-28. No other substance, seaweed or plant extract holds a 4c entry.

The EU sorts feed additives into five categories: technological, sensory, nutritional, zootechnical, and coccidiostats and histomonostats. Zootechnical authorisations under Regulation (EC) No 1831/2003 are bound to one holder, so only the named company may place 3-NOP on the EU market under entry 4c1. Generic authorisations, such as those for most vitamins and trace elements, carry no holder.

How Does 3-NOP Reduce Enteric Methane in the Rumen?#

3-NOP reduces enteric methane by binding the active site of methyl-coenzyme M reductase (MCR), the enzyme that catalyses the last step of methane formation in rumen archaea, and inactivating it by oxidising its nickel centre. Cows release methane because methanogenic archaea in the rumen form it during feed fermentation, and the cow exhales the gas.

The four steps of the 3-NOP mechanism are listed below.

1. 3-NOP binds the active site of MCR in the archaeal cell.
2. The nitrate ester oxidises the nickel centre of MCR from Ni(I), which stops the enzyme.
3. The nitrate ester is reduced to nitrite, and nitrite also inactivates MCR.
4. Hydrogen accumulates in the rumen, and fermentation shifts from acetate towards propionate and butyrate.

What happens to 3-NOP in the cow after feeding?#

3-NOP is degraded quickly and almost completely in the rumen to 1,3-propanediol, nitrate, carbon dioxide and compounds the cow already makes, such as lactose and glucose, plus the metabolite NOPA. NOPA is the residue EFSA assessed for consumer safety, because 3-NOP itself was not detected in milk or tissues. Because of this rapid degradation, 3-NOP is fed continuously in a total mixed ration (TMR).

Which Cattle and Other Ruminants Can Be Fed 3-NOP, and at What Inclusion Rate?#

3-NOP may be fed to dairy cows and cows for reproduction in the EU at 53 to 80 mg per kg complete feed (12 % moisture), to ruminants for milk production and reproduction in GB at 53 to 88 mg/kg, and to lactating dairy cows in the US at 60 to 80 mg per kg dry matter. The table compares the inclusion levels by jurisdiction, each with its basis.

The bases differ: EU and GB limits refer to complete feed at 12 % moisture, the US label to dry matter. 3-NOP is one of several cattle feed additives, and the only one with an EU or GB methane authorisation. EFSA equated the applicant's 60 to 100 mg/kg dry matter with 52.8 to 88 mg/kg complete feed at 88 % dry matter.

Dairy cows and cows for reproduction in the EU and GB#

EU law sets a legal minimum of 53 and a maximum of 80 mg 3-NOP per kg complete feed (12 % moisture) for dairy cows and cows for reproduction, under Implementing Regulation (EU) 2022/565. 3-NOP must enter feed through a premixture, never directly into compound feed.

GB allows a higher maximum of 88 mg/kg complete feed (12 % moisture) and a wider scope, "ruminants for milk production and for reproduction", which goes beyond cows. The premixture rule applies in GB as well, and the EU maximum of 80 mg/kg never applies to GB feed. In Denmark, Aarhus University recommends 60 mg 3-NOP per kg dry matter because intake fell at higher doses in Danish diets; that figure is advice, not a legal limit.

Lactating dairy cows in the US#

The US label sets 60 to 80 mg 3-NOP per kg dry matter (27.2 to 36.3 mg/lb DM) for lactating dairy cows, which equals 540 to 720 g Bovaer 10 per ton of complete feed on a 100 % dry-matter basis. The label excludes five animal groups and adds one ration limit, listed below.

• Dry cows: not for use.
• Bulls: not for use.
• Replacement heifers: not for use.
• Growing cattle: not for use.
• Other ruminants: not for use.
• Silicon dioxide: at most 2 % of complete feed from all sources.

The US label covers lactating cows only. Nutritionists can see where 3-NOP sits among feed additives for dairy cows by lactation stage.

FDA effectiveness data cover TMR with 27.3 to 31.8 % neutral detergent fibre (NDF) and 5.2 to 5.8 % crude fat, fed for no more than 105 days. Data were not evaluated at herd, farm or larger scale, so the label claim rests on those diet conditions.

Beef and feedlot cattle, sheep and goats#

No EU or US authorisation covers 3-NOP for beef cattle, sheep or goats: the EU Register shows no extension of 4c1 beyond dairy cows and cows for reproduction, and the US label excludes growing cattle and other ruminants. GB covers ruminants for milk production and for reproduction, which still excludes fattening animals.

Evidence in beef cattle exists only as research. The meta-analysis of de Oliveira and colleagues (Animal, 2026; 17 studies, 45 treatment means) found a mean reduction of 36.2 % in methane production and 33.2 % in methane yield, with efficacy falling as dietary NDF and body weight rise. Those results describe trials, not a permitted use.

For feedlot operators in the EU and the US, 3-NOP has no permitted use, because the EU entry and the US label both exclude fattening cattle. The authorised feedlot feed additives in the US do not include 3-NOP.

How Much Does 3-NOP Reduce Methane? Trial and Meta-Analysis Evidence#

In dairy cows, 3-NOP reduced methane production by 32.7 %, methane yield by 30.9 % and methane intensity by 32.6 % at a mean 70.5 mg/kg dry matter in the meta-analysis of Ermias Kebreab and colleagues (Journal of Dairy Science, 2023; 14 experiments, 48 treatment means). The six studies in the table differ in design, dose and duration.

The one-year study by Sanne van Gastelen and colleagues shows that the effect persists but varies with the diet of each lactation stage.

Fibre, fat and dose: what changes the effect#

The methane effect of 3-NOP falls by 0.633 percentage points for every 10 g/kg DM more NDF in the diet, and rises by 3.08 points for every 1 % DM less crude fat (Kebreab et al. 2023). The three modifiers that change the response are listed below.

• Fibre (NDF): higher dietary NDF lowers efficacy.
• Crude fat: higher fat lowers the additional effect of 3-NOP.
• Starch and dose: more starch and a higher 3-NOP dose increase efficacy.

The FDA effectiveness statement is likewise confined to TMR with 27.3 to 31.8 % NDF and 5.2 to 5.8 % crude fat, the diets in which effectiveness was shown. For a high-fibre ration, the Kebreab model predicts a smaller effect than the meta-analysis mean.

Bovaer, milk yield, feed intake and herd health#

Bovaer is authorised to reduce methane, not to raise milk yield, and study results on milk and intake differ by diet. van Gastelen et al. (2024) recorded 6.5 % more energy-corrected milk (ECM) over one year at 69.8 mg/kg DM, while Johansen (2023) found in Danish diets at 60 mg/kg DM that dry-matter intake (DMI) fell by 1.1 to 3.2 kg/day and ECM by 0.8 to 1.2 kg/day.

The FDA label states that milk production, feed efficiency and milk solids were not evaluated, and that a decrease in DMI may be observed in some animals. Aarhus University's 2026 on-farm study of 73 Danish herds found no clear overall negative effect on milk yield, disease or mortality, but did not exclude problems in single herds; a welfare study is due in 2028.

Which Forms and Grades of 3-NOP Are Sold?#

3-NOP is sold as Bovaer 10, a white, free-flowing granular powder with at least 10 % 3-NOP on a silicic acid carrier with propylene glycol, made by dsm-firmenich. No second grade or producer of a 3-NOP feed preparation is on record. The table lists the specification values from the EU act, the EFSA opinion and the US label.

The EU particle limits keep fine dust out of the product, which matters for worker exposure in feed mills.

What Is the Regulatory Status of 3-NOP? EU, US and GB Side by Side#

3-NOP is authorised in the EU (4c1, until 2032-04-28) and in GB (in force since 2023-12-22), while in the US it is an unapproved animal drug that the FDA allows to be marketed under enforcement discretion. The matrix below compares the three jurisdictions, status 3 November 2026.

EU Register entry 4c1 under Implementing Regulation (EU) 2022/565#

Implementing Regulation (EU) 2022/565 authorised 3-NOP as 4c1 from 2022-04-28 to 2032-04-28 for dairy cows and cows for reproduction, with a minimum of 53 and a maximum of 80 mg/kg complete feed (12 % moisture) and no withdrawal period. Entry 4c1 in the EU Register of Feed Additives lists holder, species and limits, and it names 3-NOP as the only member of functional group 4c.

The act adds conditions of use. 3-NOP enters feed only as a premixture; operators set procedures against inhalation, skin and eye exposure and use personal protective equipment where risks cannot be reduced; official control uses RP-HPLC-UV (EURL FAD-2019-0057). Implementing Regulation (EU) 2026/98 of 15 January 2026 moved the holder to dsm-firmenich Switzerland Ltd., and stocks labelled before may be used until exhausted.

Is Bovaer approved in the US?#

No: Bovaer is not an FDA-approved drug; FDA's Center for Veterinary Medicine told Elanco US Inc. on 2024-05-24 (letter G-150438) that it does not intend to take enforcement action while Bovaer 10 is marketed as labelled. Bovaer has no new animal drug application (NADA), no 21 CFR section, no GRAS status and no AAFCO definition.

None of the routes of US feed additive regulation (food additive petition, GRAS, AAFCO) covers Bovaer. The FDA letter finds that Bovaer 10 is a drug under section 201(g)(1) of the FD&C Act, and states that CVM does not intend to enforce approval, current good manufacturing practice, adverse-event reporting, labelling and registration requirements as long as it has no questions.

The label claim reads "reduction of methane gas emissions per pound of dry matter intake", for lactating dairy cows only. The label also warns that the product may damage male fertility and reproductive organs.

Bovaer in the UK: the GB authorisation#

GB authorises 4c1 for ruminants for milk production and for reproduction at 53 to 88 mg/kg complete feed (12 % moisture), in force since 2023-12-22 under S.I. 2023/1196 (England), SSI 2023/339 (Scotland) and S.I. 2023/1276 (W. 224) (Wales). The directions for use must state storage conditions and heat stability.

The schedule names DSM Nutritional Products Ltd as holder and prints no end date. A GB feed additive authorisation runs ten years under Article 9(7), as the Explanatory Note to S.I. 2023/1196 states.

Bovaer in Denmark: the national feeding rule#

Denmark requires conventional dairy herds with more than 50 cows to feed Bovaer for at least 80 days in 2025 or to feed high-fat rations all year, as reported by Aarhus University's DCA. Organic herds fall outside the rule.

Denmark has also proposed a factor of -27 % methane yield at 60 mg 3-NOP/kg DM for its national greenhouse gas inventory (Lund et al. 2024), subject to UN and IPCC approval.

Is 3-NOP allowed in EU organic feed?#

3-NOP is not permitted in EU organic feed, because Implementing Regulation (EU) 2021/1165 Annex III limits zootechnical additives in organic production to enzymes and microorganisms.

The list of feed additives in organic production has no 4c entry, so an EU organic ration cannot include Bovaer 10.

Is Bovaer Safe? Target Animal, Consumer, User and Environment#

EFSA's FEEDAP Panel concluded in 2021 that 3-NOP is safe for dairy cows at 100 mg/kg dry matter, safe for consumers and of no concern for the environment, but that it may be harmful by inhalation and irritates skin and eyes of workers. The table gives the conclusion for each receptor from the EFSA opinion (EFSA Journal 2021;19(11):6905) and the US label.

For feed and regulatory staff, the consumer row means that EFSA set an acceptable daily intake (ADI) of 1 mg per kg body weight and applied it to NOPA, the residue that remains after rumen degradation. No maximum residue limit (MRL) is set for 3-NOP or NOPA.

Bovaer side effects in cows#

EFSA found 3-NOP safe for dairy cows at 100 mg/kg dry matter (88 mg/kg complete feed) but established no margin of safety and drew no conclusion for other ruminant categories; at twice that level, dry-matter intake fell by 4 %. The US label notes that a decrease in DMI may be observed in some animals. The Aarhus University study of 73 Danish herds (2026) found no clear overall negative effect on milk yield, disease or mortality and did not exclude problems in single herds.

Handling 3-NOP safely in feed mills and premix plants#

Feed mill and premix workers need protection from 3-NOP dust, because EFSA considers the additive possibly harmful by inhalation and a skin and eye irritant, and the act requires PPE where risks cannot be reduced. The three protection points for plant staff are listed below.

• Inhalation: dust from the granular powder (dusting potential up to 390 mg/m3) calls for organisational measures and respiratory protection.
• Skin and eyes: 3-NOP irritates skin and eyes; it is not a skin sensitiser.
• PPE: eye, skin and breathing protection where procedures cannot reduce the risk.

EFSA could not fully clarify the genotoxicity of 3-NOP, and the US label warns that the product may damage male fertility and reproductive organs. 3-NOP has no harmonised CLP classification (no Annex VI entry); the ECHA C&L notified classification is Repr. 2 H361, Acute Tox. 4 H302, Skin Irrit. 2 H315 and Eye Dam. 1 H318. For handling details, see the product SDS.

How Stable Is 3-NOP in Premixes and Pellets, and What Does It Interact With?#

3-NOP is most stable in mineral premixtures, where 98.3 to 98.8 % remained after 6 months at 25 °C (77 °F), and least stable in mineral complementary feed, where 67 to 69.5 % remained. The table compares recoveries by matrix and conditions, as EFSA reported them in 2021.

These recoveries fit the premixture route that the EU and GB acts prescribe, and GB directions for use must state storage conditions and heat stability.

Interactions come from the diet. Higher NDF and crude fat reduce the methane effect, while starch and dose increase it (Kebreab et al. 2023). In the US, silicon dioxide from all sources, including the Bovaer 10 carrier, must stay at or below 2 % of complete feed.

How to Source 3-NOP: Specification Checklist for Feed Mills and Premixers#

Buyers source 3-NOP as Bovaer 10 through the authorisation holder's distribution, so the specification check centres on the authorisation, the premixture route and storage rather than on comparing producers. The seven checklist items for a purchase are listed below.

• Authorisation: EU entry 4c1 and the holder dsm-firmenich Switzerland Ltd. on the label.
• Active content: minimum 10 % 3-NOP on the certificate of analysis.
• Particle size: below 50 µm under 0.5 % and below 10 µm 0 %.
• Incorporation: premixture only, with inclusion between 53 and 80 mg/kg complete feed (12 % moisture) in the EU.
• Storage: below 25 °C (77 °F) and a 36-month best-use date.
• Analytical method: RP-HPLC-UV (EURL FAD-2019-0057) for checks of premixtures and feed.
• Safety data sheet: SDS on file for worker protection.

Price depends on volume, destination and the certification the buyer needs, so quotes vary by order. Quality schemes such as FAMI-QS and GMP+ are named in the quote request, not on the EU entry.

Frequently Asked Questions about Bovaer#

The three questions below come up most often about Bovaer.

What are the effects of Bovaer on humans?#

Milk from cows fed Bovaer contains no detectable 3-NOP: EFSA found the metabolite NOPA at no more than 3.66 µg/kg milk, and the most exposed consumer group reaches 0.06 % of the acceptable daily intake of 1 mg/kg body weight. Tissues contained NOPA below 5 µg/kg, and EFSA set no maximum residue limit. Worker exposure to the additive itself is a separate question, covered in the handling section above.

What is Bovaer 10?#

Bovaer 10 is the commercial preparation of 3-NOP: at least 10 % active substance on silica with propylene glycol. The product is a white granular powder, sold in 20 kg bags in the US.

Why is Bovaer controversial?#

Bovaer is debated over milk safety and cow welfare; the EFSA opinion, the GB authorisation and the 2026 Aarhus herd study address both points. EFSA found consumer exposure at 0.06 % of the ADI and found 3-NOP safe for dairy cows at 100 mg/kg dry matter. GB authorised 4c1 in 2023, and the Aarhus study of 73 Danish herds found no clear overall negative effect on milk yield, disease or mortality.

How Does 3-NOP Differ from Seaweed, Nitrate, Monensin, Essential Oils and Tannins?#

3-NOP is the only methane-reducing feed additive with an EU authorisation in functional group 4c, a GB authorisation and an FDA enforcement-discretion letter; seaweed, nitrate, monensin, essential oils and tannins act differently and hold no 4c entry. The table compares the five alternatives by mechanism, status and evidence.

3-NOP and bromoform both act on enzymes of methanogenesis, while monensin, essential oils and tannins change rumen fermentation more broadly. Feeding cows Asparagopsis seaweed reduces methane through bromoform, but it holds no EU or US authorisation.

Methane reductions from 3-NOP enter carbon claims through national inventory factors and voluntary methodologies such as Verra VM0041, not through the feed authorisation. The rules for how methane additive claims are measured and credited sit on a separate page.