Monensin: veterinary dose and monograph

At a glance

Drug class

Antiparasitic

Also known as

Rumensin, Coban, Elancoban

Species with doses

Cattle, Goats, Sheep and Poultry

General dose range

1–2 mg/kg PO daily (in feed) — check the species tables for the indication

Routes

PO

Last reviewed

1 October 2026

Indications

• Coccidiosis prevention in poultry, cattle, sheep and goats
• Rumen fermentation modifier — improved feed efficiency / weight gain in cattle
• Reduction of subacute ruminal acidosis and bloat
• Ketosis-risk reduction in transition dairy cows (controlled-release bolus, where licensed)

Monensin dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Cattle

• Rumen modifier / coccidiosis (in feed): Product label (feed premix) — neither Papich 5e nor Plumb’s has a monensin monograph. Dosed as g/ton of complete feed per label; mix accurately. FATAL to horses and other equids — keep medicated feed away from them; never combine with tiamulin.

Horses

• CONTRAINDICATED — fatal: Ionophores cause fatal cardiomyopathy and rhabdomyolysis in equids even from contaminated feed. Keep cattle/poultry feed containing monensin away from horses.

Goats

• Coccidiosis prevention (in feed): Label-sourced (feed premix, ~20 g per ton of feed) — neither Papich 5e nor Plumb’s has a monensin monograph. Narrow safety margin — accurate mixing is essential; fatal to equids and when over-mixed. Never combine with tiamulin. Follow the label withdrawal.

Sheep

• Coccidiosis (in feed, where permitted): Product label where permitted — neither Papich 5e nor Plumb’s has a monensin monograph. Sheep are more ionophore-sensitive than cattle; never overdose. Fatal to equids; not with tiamulin.

Poultry

• Coccidiosis (broilers, in feed): Label-sourced (feed premix) — neither Papich 5e nor Plumb’s has a monensin monograph. Dosed by feed concentration (~90–110 ppm) per the label; follow its withdrawal. Do NOT use with tiamulin (toxic interaction); fatal to equids.

Buffalo

No buffalo-specific doses are on file, so buffalo are dosed as cattle.

• Rumen modifier / coccidiosis (in feed): Product label (feed premix) — neither Papich 5e nor Plumb’s has a monensin monograph. Dosed as g/ton of complete feed per label; mix accurately. FATAL to horses and other equids — keep medicated feed away from them; never combine with tiamulin.

Contraindications

HORSES and other equids — never (fatal cardiotoxicity). Dogs (very toxic). Concurrent tiamulin/other potent CYP inhibitors in target species (potentiate ionophore toxicity). Lactating dairy where not permitted. Overdose / feed-mixing errors. Known hypersensitivity.

Species-specific warnings

Horses: FATAL — ionophores cause lethal cardiac/skeletal myonecrosis in horses. Even trace contamination of equine feed can kill. Never allow access.

Dogs: Highly toxic to dogs (cardiotoxic/myotoxic) — keep monensin-medicated feed away from dogs.

Adverse effects

• Reduced feed intake at higher inclusion
• Toxicity: anorexia, diarrhoea, weakness, myocardial/skeletal muscle degeneration, heart failure, death (overdose or sensitive species)
• Decreased performance if overdosed

Drug interactions

• Tiamulin / other CYP3A inhibitors: block ionophore metabolism → severe, often fatal toxicity (NEVER combine)
• Macrolides, chloramphenicol, sulfonamides: some potentiate ionophore toxicity
• No therapeutic systemic drug pairing — it is a feed additive

Pregnancy and lactation

Used at label inclusion in breeding/pregnant ruminants and poultry; the dominant safety issue is overdose/wrong-species exposure, not pregnancy per se.

Monitoring

• Accurate feed inclusion (mixing) — the commonest cause of toxicosis is a mixing error
• Target-species performance/intake
• Cardiac signs (any exposed horse is an emergency: troponin, ECG, echo)
• Strict separation of medicated feed from equids

Toxicity and overdose

Ionophore toxicosis is the defining hazard: dose-dependent myocardial and skeletal muscle degeneration → weakness, recumbency, tachycardia/arrhythmia, dyspnoea, and death; survivors may have permanent heart damage/heart failure. HORSES are exquisitely sensitive (even small contamination is fatal); dogs are also highly sensitive. Tiamulin co-exposure dramatically lowers the toxic threshold.

Management: No specific antidote. Remove the contaminated feed immediately; decontaminate (activated charcoal early). Provide intensive supportive/cardiac care — strict stall rest (avoid exertion, which precipitates fatal arrhythmia), IV fluids, anti-arrhythmics as indicated, and serial cardiac troponin/echocardiography. Prognosis is guarded once myocardial necrosis occurs; vitamin E/selenium has been used adjunctively.

Clinical pearls

• Lifesaving for ruminant/poultry coccidiosis and feed efficiency — but a notorious killer of HORSES; the two must never meet
• The classic poisoning is a horse (or dog) eating cattle/poultry feed, or a feed-mixing error — both are emergencies with a guarded prognosis
• NEVER combine with tiamulin (or certain other CYP inhibitors) — the interaction can be fatal even in target species
• Sheep have a narrower safety margin than cattle — mix and dose precisely
• Store and label ionophore feeds rigorously to prevent cross-contamination

Mechanism of action

A lipophilic ionophore that inserts into cell membranes and shuttles cations (especially Na+, and K+) across them, collapsing transmembrane ion gradients. In coccidia/Gram-positive rumen bacteria this is lethal/inhibitory (favouring propionate-producing flora — the feed-efficiency benefit). In mammalian (especially equine) cardiac and skeletal muscle the same ion disruption causes calcium overload, mitochondrial failure and myonecrosis — the basis of its lethal cardiotoxicity.

Formulations and products

• Feed premix (e.g. Rumensin 100/200 g/kg)
• Controlled-release rumen bolus
• Rumensin (Elanco) — Monensin sodium premix / controlled-release bolus, Feed premix / rumen bolus
• Coban / Elancoban (Elanco) — Monensin poultry premix, Feed premix

Storage

Premix/bolus: 15–30 °C, dry; store SECURELY and clearly labelled away from any feed for horses/dogs. Prevent cross-contamination of equine rations during mixing.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other antiparasitics

• Mebendazole
• Meglumine Antimoniate
• Melarsomine
• Milbemycin oxime
• Monepantel
• Morantel
• Moxidectin
• Nicarbazin

Frequently asked questions