Monensin: Coccidiostat Uses, Species, Dosage, Withdrawal and Approval Status

Monensin sodium is a polyether ionophore coccidiostat that the EU authorises for chickens and turkeys as Coxidin (identification number 51701) and the US approves for poultry, cattle and goats under 21 CFR 558.355. In the EU, feed for chickens for fattening must contain between a legal minimum of 100 and a legal maximum of 120 mg monensin sodium per kg complete feed (12 % moisture), and no withdrawal period applies.

The EU entry covers poultry only and runs to 2036-04-01, while the US classes monensin as a Category I drug that is not a Veterinary Feed Directive drug. Monensin belongs to category 5 among the feed additive categories of Regulation (EC) No 1831/2003, the category of coccidiostats and histomonostats.

The same molecule thus works under two legal frames: an EU poultry coccidiostat with maxima and carry-over limits, and a US medicated-feed drug for poultry, cattle and goats dosed in g/ton.

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

What Is Monensin?#

Monensin is a carboxylic polyether ionophore made by Streptomyces fermentation and used in feed as its sodium salt, monensin sodium (C36H61NaO11, 692.9 g/mol, CAS 22373-78-0). The US introduced it in July 1971 (Chapman, Jeffers and Williams, Poultry Science, 2010).

Feed use has two jobs: control of Eimeria, the parasites behind coccidiosis, in poultry, and in US cattle also rumen modification for feed efficiency and milk production efficiency.

How is monensin produced? Streptomyces fermentation and monensin A#

Coxidin is produced by fermentation with the strain Streptomyces sp. LMG S-19095, and Implementing Regulation (EU) 2026/532 requires at least 90 % monensin A and at least 95 % monensin A plus B. Elancoban, described in Regulation (EC) No 1356/2004, is a dried fermentation product of Streptomyces cinnamonensis ATCC 15413.

Who holds the monensin authorisations, and which trade names exist?#

Huvepharma N.V. holds EU entry 51701 for Coxidin under Implementing Regulation (EU) 2026/532, and Regulation (EC) No 1356/2004 names Elanco GmbH as holder for Elancoban (E 757), with trade names such as Elancoban G200 and Elancogran 100. Huvepharma NV also holds Monimax (51776), a fixed combination of monensin with nicarbazin.

In the US, 21 CFR 558.355 lists two sponsors of monensin Type A medicated articles: Elanco US Inc. (sponsor code 058198) and Huvepharma EOOD (016592, Type A 90.7 g/lb). Rumensin, the name cattle producers search for, and Coban, a US poultry name, are trade names of monensin, while the sponsor listing identifies the approved article.

Which EU Category Covers Monensin?#

Monensin sodium belongs to category 5 of Regulation (EC) No 1831/2003, coccidiostats and histomonostats, a category without functional groups whose authorisations are bound to one holder. Each preparation has its own entry, holder, species list and limits.

The EU frame is narrower than the US one. Authorisation under Regulation (EC) No 1831/2003 covers chickens and turkeys only. Monensin holds no EU feed additive authorisation for cattle, sheep, goats or any other ruminant (Article 11(2)), so the US cattle uses have no EU counterpart.

Monensin sodium was one of the last four EU antibiotic growth promoters, together with salinomycin sodium, avilamycin and flavophospholipol. These four were marketed until 31 December 2005 and deleted as growth promoters from 1 January 2006, while monensin stayed in the EU Register as an authorised coccidiostat.

How Does Monensin Work? Mode of Action against Eimeria#

Monensin acts as a monovalent ionophore: it forms lipid-soluble complexes with sodium and potassium ions and raises the membrane permeability of Eimeria sporozoites and early trophozoites. The three steps of the mechanism are listed below.

1. Monensin binds sodium (Na+) and potassium (K+) ions into lipid-soluble complexes.
2. The complexes carry the ions across the membranes of sporozoites and early trophozoites.
3. Membrane permeability of these early Eimeria stages rises.

Ionophores differ by the ions they carry. Monensin, narasin and salinomycin are monovalent ionophore coccidiostats, while lasalocid is divalent.

Ionophores allow some leakage of oocysts, so birds still develop immunity to Eimeria (Noack et al. 2019).

What monensin changes in the rumen#

In the rumen, monensin shifts fermentation so that less acetate forms relative to propionate, and less methane forms.

The methane effect is small. In the meta-analysis of Marumo and colleagues (Animals, 2023), monensin at or below 24 mg/kg dry matter reduced methane production by 5.4 % and methane yield by 4.0 % in dairy cows, a small effect among methane-reducing feed additives, and monensin holds no EU methane authorisation.

Which Animals Can Be Fed Monensin, and at What Inclusion Rate?#

Monensin may be fed to chickens and turkeys in the EU at 60 to 120 mg per kg complete feed (12 % moisture), and in the US to broilers, growing turkeys, bobwhite quail, cattle and confined goats at the levels of 21 CFR 558.355. The table compares each animal group with its basis, in the units each instrument uses.

Chickens and turkeys in the EU#

Entry 51701 sets 100 to 120 mg monensin sodium per kg complete feed (12 % moisture) for chickens for fattening and for chickens reared for laying up to 16 weeks, and 60 to 100 mg/kg for turkeys for fattening and turkeys reared for reproduction up to 16 weeks. Pullets past 16 weeks and hens in lay fall outside the entry.

A legal minimum is a floor, not a dose: feed outside the range is outside the authorisation. EFSA's FEEDAP Panel found monensin efficacious at 100 mg/kg in chickens and at 60 mg/kg in turkeys in its 2024 opinion.

Broilers, growing turkeys and bobwhite quail in the US#

21 CFR 558.355 approves monensin for broiler chickens at 90 to 110 g/ton (99 to 121 mg/kg) with a claim for the prevention of coccidiosis, for growing turkeys at 54 to 90 g/ton and for bobwhite quail at 73 g/ton. The US label also warns that monensin may interfere with the development of immunity in turkeys.

Monensin for cattle in the US: feedlot, pasture, dairy and calves#

Feedlot cattle receive 5 to 40 g monensin per ton of complete feed (50 to 480 mg per head per day) for improved feed efficiency and 10 to 40 g/ton for coccidiosis, and 21 CFR 558.355 states no added feed-efficiency response above 30 g/ton (360 mg/head/day). The five other US cattle uses are listed below.

• Pasture cattle: a protein-mineral block offers 80 to 200 mg/head/day at one block per 5 head, with no salt offered.
• Beef cows: 50 to 200 mg/head/day in at least 1 lb of feed, at most 100 mg in the first 5 days.
• Dairy cows on a TMR: for "increased milk production efficiency".
• Dairy cows in component feeding: 185 to 660 mg/head/day lactating, 115 to 410 mg/head/day dry.
• Calves excluding veal calves: 0.14 to 1.0 mg/lb body weight per day.

On the US label, Rumensin improves feed efficiency, weight gain and milk production efficiency in cattle; none of these uses exists in the EU.

Monensin for goats: confined goats in the US only#

The US approves monensin for goats in confinement at 20 g/ton of complete feed, and 21 CFR 558.355 states that the feed must not be given to lactating goats. The approval excludes sheep, and no EU entry names goats.

Animals with no monensin authorisation: horses, pigs, sheep and EU ruminants#

Horses, pigs and sheep have no monensin approval in the US and no monensin entry in the EU, and no ruminant has an EU monensin entry.

Horses are the most sensitive species measured. Kexxtone, a monensin intraruminal bolus, is an EU veterinary medicine rather than a feed additive.

What Do EFSA and Meta-Analyses Show for Monensin?#

In lactating dairy cows, monensin raised milk yield by 0.7 kg/day, cut dry-matter intake by 0.3 kg/day and improved milk production efficiency by 2.5 % in the meta-analysis of Duffield, Rabiee and Lean (Journal of Dairy Science, 2008; 77 trials, 9,677 cows). The table compares the five main evidence sources by design, animals and dose.

The cattle results, including the dairy meta-analysis, describe US uses, not EU authorisations.

Efficacy against Eimeria in chickens and turkeys#

EFSA's FEEDAP Panel concluded in 2024 that Coxidin is efficacious against coccidiosis in chickens and turkeys and noted signs of Eimeria resistance to monensin.

Resistance has a long history: the first field resistance was reported in the USA in 1974 (Noack et al. 2019), and feed mills and integrators manage it through anticoccidial programmes.

Implementing Regulation (EU) 2026/532 adds EU field monitoring of Eimeria resistance from 1 April 2031.

Feed efficiency, milk and bloat in cattle#

In growing and finishing beef cattle, the meta-analysis of Duffield, Merrill and Bagg (Journal of Animal Science, 2012) found an improvement in feed efficiency of about 6.4 %, but only 2.5 to 3.5 % in the last two decades, at a mean 28.1 mg/kg dry matter. The effect rose linearly with dose and was larger on corn silage diets.

In stocker cattle on forage, the meta-analysis of Gadberry and colleagues (Translational Animal Science, 2022; 38 experiments) found 10.6 kg more ending body weight after 112 days, a 20 % lower bloat incidence and a bloat severity score 0.7 points lower.

Which Forms and Grades of Monensin Are Sold? Premixtures and Type A Medicated Articles#

Monensin is sold in the EU as Coxidin, a preparation with 23.7 to 26.2 % monensin activity on wheat bran or calcium carbonate, and as Elancoban granules with 10 or 20 % activity, and in the US as Type A medicated articles of 45 to 113.4 g/lb. The table compares the forms by activity, carrier and instrument.

US feed mills dilute the concentrate. Under 21 CFR 558.4, Type A medicated articles are diluted to Type B feeds of at most 40 g/lb and then to Type C complete feeds.

In the US, Type C assay limits apply by level, for example 80 to 120 % of the label value for cattle feed at 5 to 10 g/ton.

What Is the Regulatory Status of Monensin? EU, US and GB Side by Side#

Monensin sodium is authorised in the EU for chickens and turkeys as entry 51701, approved in the US for poultry, cattle and goats under 21 CFR 558.355, and listed as authorised in GB. The matrix compares the three jurisdictions, status 3 November 2026.

EU Register entry 51701 under Implementing Regulation (EU) 2026/532#

Implementing Regulation (EU) 2026/532 of 11 March 2026 renewed and extended Coxidin as entry 51701 from 1 April 2026 until 2036-04-01, cut the chicken maximum from 125 to 120 mg/kg and added turkeys reared for reproduction. Entry 51701 in the EU Register of Feed Additives names the holder, the four bird categories and their limits.

The act sets three conditions of use: no mixing with other coccidiostats, the label warning "Dangerous for equines" with advice to avoid simultaneous administration with tiamulin, and post-market monitoring of Eimeria resistance. Additive and premixtures labelled before 1 October 2026 and compound feed labelled before 1 April 2027 under the old rules may be used up.

Elancoban under Regulation (EC) No 1356/2004#

Regulation (EC) No 1356/2004, whose Annex was replaced by Regulation (EC) No 1096/2008 and whose holder name was changed by Implementing Regulation (EU) 2019/138, sets Elancoban (E 757) at 100 to 125 mg/kg for chickens for fattening, 100 to 120 mg/kg for chickens reared for laying and 60 to 100 mg/kg for turkeys up to 16 weeks, with a withdrawal period of 1 day. The holder is Elanco GmbH. For the Elancoban entry: printed expiry 2014-07-30; the EU Register records an application under Article 10(2) of Regulation (EC) No 1831/2003 and still lists the entry pending the Commission decision.

Is monensin approved in the US? 21 CFR 558.355#

Yes: monensin is an approved new animal drug under 21 CFR 558.355 and a Category I drug under 21 CFR 558.4 (eCFR current to 2026-10-30).

Ionophores are not medically important antimicrobials, and monensin is sold over the counter in medicated feed. It is not a VFD drug, so monensin needs no Veterinary Feed Directive order from a veterinarian.

Monensin feeds carry the label statement that they are safe for cattle and goats only, and the label warns that monensin is fatal to horses.

Monensin in GB and Canada#

The FSA register lists 51701 monensin sodium (Coxidin) as authorised in England, Scotland and Wales under GB legislation of 2024 (register read 2026-11-03).

Buyers for GB feed check the FSA register, which records each GB feed additive authorisation by identification number. In Canada, monensin is a veterinary non-prescription drug with a Drug Identification Number (DIN), for example monensin sodium 200 g/kg in the Health Canada Drug Product Database.

Monensin withdrawal times and maximum residue limits#

Entry 51701 sets no withdrawal period, and EFSA found that the existing maximum residue limits (MRLs) ensure consumer safety without one; 21 CFR 558.355 lists no withdrawal for broilers, turkeys or cattle. In the US, a withdrawal period is not established for pre-ruminating calves, and the label excludes veal calves.

The EU MRLs for poultry are 25 µg/kg wet skin and fat and 8 µg/kg wet liver, kidney and muscle. The US tolerances under 21 CFR 556.420 are 0.10 ppm in cattle liver and 0.05 ppm in muscle, kidney and fat.

Monensin carry-over maxima under Directive 2002/32/EC#

Directive 2002/32/EC, Annex I Section VII as replaced by Regulation (EU) No 574/2011, caps unavoidable monensin carry-over at 1.25 mg/kg in feed materials and in compound feed for sensitive animals, and at 3.75 mg/kg in compound feed for other species (12 % moisture). These maxima apply the general rules on coccidiostat carry-over to non-target feed.

The sensitive group covers equines, dogs, sheep and goats, ducks, bovines, dairy cattle, laying birds, chickens reared for laying and turkeys past 16 weeks, and withdrawal feed. A premixture for feed in which monensin is not authorised may cause at most 50 % of the compound-feed maximum. Regulation (EC) No 124/2009 sets food maximum levels for monensin in non-target animals other than chickens for fattening, turkeys and bovines: 8 µg/kg in liver and 2 µg/kg in other tissues, wet weight.

Is Monensin Toxic? Target Animal, Consumer, User and Environment#

EFSA's FEEDAP Panel concluded in 2025 that Coxidin is safe for chickens up to 120 mg/kg feed and for turkeys up to 100 mg/kg without a margin of safety, safe for consumers under existing MRLs and safe for the environment, while the dust is an inhalation risk for workers. The table gives each receptor from the EFSA opinion (EFSA Journal 2025;23:e9541) and the US label.

EFSA's target-animal conclusions changed between opinions. It found 125 mg/kg safe for chickens and 100 mg/kg for turkeys in 2005, with a margin below two, and in 2024 could not confirm that 125 mg/kg remains safe for chickens.

Why monensin is dangerous for horses#

Monensin is dangerous for horses because horses have the lowest acute oral LD50 of the species measured: 1 to 3 mg/kg body weight, against 200 to 214 mg/kg in chickens (Ekinci et al. 2023, review).

The EU label of entry 51701 must carry the words "Dangerous for equines". Feed mills and makers of horse feed additives work to the 1.25 mg/kg carry-over maximum that applies to compound feed for equines.

EFSA's CONTAM Panel (Dorne et al. 2013, Toxicology and Applied Pharmacology) found the risk from 2, 5 or 10 % cross-contamination of feed negligible, except for monensin above 5 % in horses.

Monensin toxicity in cattle and goats: mixing errors#

Monensin is toxic to cattle and goats when mixing errors raise the dose: the US label warns that such errors can be fatal to cattle and could be fatal to goats. The acute oral LD50 is 20 to 80 mg/kg body weight in cattle, 26.4 mg/kg in goats and 12 mg/kg in sheep (Ekinci et al. 2023).

Handling monensin premixtures safely#

Monensin premixtures need dust control in the plant, because EFSA found both Coxidin forms an inhalation risk, the calcium-carbonate form a skin and respiratory sensitiser and the wheat-bran form an eye irritant. The three protection points are listed below.

• EU rule: breathing, eye and skin protection where procedures cannot eliminate the risk (Implementing Regulation (EU) 2026/532).
• US rule: protective clothing, impervious gloves and a dust mask for Type A articles (21 CFR 558.355(d)(5)).
• Hazard classification: see the product SDS.

How Stable Is Monensin, and What Does It Interact With?#

Monensin must never be combined with another coccidiostat in the EU, and tiamulin, erythromycin, chloramphenicol and certain sulfonamides can cause toxic interactions with it. The four interaction risks are listed below.

• Other coccidiostats: entry 51701 forbids mixing with any other coccidiostat.
• Tiamulin: avoid simultaneous administration (EU label); incompatible (US label).
• Erythromycin and chloramphenicol: toxic interaction (Noack et al. 2019).
• Certain sulfonamides: toxic interaction (Noack et al. 2019).

The supplier must state storage conditions and heat-treatment stability. In the US, liquid feeds with monensin need recirculation or agitation. Official control uses EN ISO 14183 (HPLC with post-column derivatisation) for premixtures and compound feed, and EN 17299 (LC-MS/MS) at carry-over levels.

How to Source Monensin: Specification Checklist for Feed Mills and Premixers#

Buyers source monensin as a holder-bound coccidiostat, so the specification check starts with the authorisation entry and the holder, then the activity, carrier and label warnings. The seven checklist items are listed below.

• Authorisation: entry 51701 and Huvepharma N.V., or the US sponsor and 21 CFR 558.355.
• Activity: monensin activity on the certificate of analysis.
• Carrier: wheat bran or calcium carbonate for Coxidin.
• Label warnings: "Dangerous for equines" and the tiamulin warning.
• Transition labels: old-label stock within the 2026/532 use-up dates.
• Analytical method: EN ISO 14183.
• Safety data sheet: SDS on file for worker protection.

Price depends on form, activity, volume, destination and certification, so quotes vary by order.

Frequently Asked Questions about Monensin#

The five questions below come up most often about Rumensin and monensin.

Is Rumensin an antibiotic?#

Rumensin is a trade name of monensin, an ionophore antibiotic that is not used in human medicine and is not on the WHO list of medically important antimicrobials.

In the EU, the growth-promoter use of monensin ended on 1 January 2006, when the last antibiotic growth promoters were deleted, while its coccidiostat entries stayed.

What is another name for Rumensin?#

Rumensin is a trade name for monensin sodium, which is also sold as Coban, Coxidin and Elancoban. Monensin and Rumensin are the same active substance.

Is Rumensin safe for pigs?#

No: monensin has no US approval and no EU entry for pigs, and its acute oral LD50 in swine is 8.9 mg/kg body weight (Ekinci et al. 2023). Pigs are not a target species in 21 CFR 558.355 or in entry 51701.

Does Rumensin help with coccidiosis?#

Yes: 21 CFR 558.355 includes coccidiosis claims for broilers and for cattle at 10 to 40 g/ton, and the EU authorises monensin as a coccidiostat for chickens and turkeys.

Monensin is one tool of coccidiosis control in poultry and cattle.

Is monensin harmful to humans?#

Residues of monensin in meat stay within limits set from an EU acceptable daily intake of 0.003 mg/kg body weight and a US one of 12.5 µg/kg body weight, and EFSA found that existing MRLs ensure consumer safety without a withdrawal period. The EU sets MRLs for poultry tissues, and the US sets tolerances for cattle tissues under 21 CFR 556.420.

How Does Monensin Differ from Lasalocid, Salinomycin, Narasin, Nicarbazin and Coccidiosis Vaccines?#

Monensin is a monovalent ionophore like narasin and salinomycin, while lasalocid is divalent, nicarbazin is a chemical coccidiostat and coccidiosis vaccines are veterinary medicinal products rather than feed additives. The table compares the alternatives by class, US section and the main difference from monensin.

Lasalocid differs from monensin as a divalent ionophore with its own species list. Monimax, held by Huvepharma NV under Implementing Regulation (EU) 2020/994, combines monensin and nicarbazin at 40 + 40 to 50 + 50 mg/kg complete feed, with expiry 2030-07-30.