# Monensin: veterinary dose and monograph

> Monensin is a veterinary antiparasitic. Polyether IONOPHORE — an in-feed anticoccidial (poultry) and rumen modifier (cattle) that improves feed efficiency, controls coccidiosis and reduces bloat/acidosis and ketosis risk. Indications include 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. This monograph lists 4 reference doses for cattle, goats, sheep and poultry, each with route, frequency and source, plus meat and milk withdrawal periods for food animals.

Source: https://vetmasterji.com/drugs/monensin · Last reviewed: 2026-10-01

## 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

*Monensin doses for cattle*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Rumen modifier / coccidiosis (in feed) | 1–2 mg/kg | PO | daily in feed | — | Withdrawal NOT established — treat as extra-label |

- 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

*Monensin doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| CONTRAINDICATED — fatal | Never feed to horses, donkeys or mules — ionophore toxicity is fatal at very low doses | — | — | — |

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

### Goats

*Monensin doses for goats*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Coccidiosis prevention (in feed) | ~20 g per ton of feed, continuously | PO | continuous in feed | — | Withdrawal NOT established — treat as extra-label |

- 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

*Monensin doses for sheep*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Coccidiosis (in feed, where permitted) | 1 mg/kg | PO | daily | — | Withdrawal NOT established — treat as extra-label |

- 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

*Monensin doses for poultry*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Coccidiosis (broilers, in feed) | ~90–110 ppm in feed, continuously | PO | continuous in feed | — | Withdrawal NOT established — treat as extra-label |

- 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.

*Monensin doses for buffalo*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Rumen modifier / coccidiosis (in feed) | 1–2 mg/kg | PO | daily in feed | — | Withdrawal NOT established — treat as extra-label |

- 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

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

> **Caution:** 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

> **Caution:** 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.

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## Frequently asked questions

### What is the dose of Monensin for cattle?

Reference doses for Monensin in cattle: 1–2 mg/kg PO daily in feed (Rumen modifier / coccidiosis (in feed)). Confirm against the label and the patient before use.

### Can Monensin be given to horses?

Never feed to horses, donkeys or mules — ionophore toxicity is fatal at very low doses (CONTRAINDICATED — fatal).

### What is the dose of Monensin for goats?

Reference doses for Monensin in goats: ~20 g per ton of feed, continuously PO continuous in feed (Coccidiosis prevention (in feed)). Confirm against the label and the patient before use.

### What is the withdrawal period for Monensin?

Cattle, PO (Rumen modifier / coccidiosis (in feed)): Withdrawal NOT established — treat as extra-label; Goats, PO (Coccidiosis prevention (in feed)): Withdrawal NOT established — treat as extra-label; Sheep, PO (Coccidiosis (in feed, where permitted)): Withdrawal NOT established — treat as extra-label; Poultry, PO (Coccidiosis (broilers, in feed)): Withdrawal NOT established — treat as extra-label. Follow the product label and national regulations where they differ.

### When should Monensin not be used?

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.

### What are the side effects of Monensin in animals?

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.

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.