Ionophore toxicity

Ionophore toxicity is rare in pigs, but when it occurs, it affects skeletal muscle and may present neurological, respiratory, or locomotive symptoms, making for a challenging diagnosis.

Alternative names: narasin toxicity

Ionophores are used as feed additives to improve feed efficiency and average daily gain. Ionophores work by changing bacterial flora, decreasing butyric and acetic acid production and promoting propionic acid production, which is more energy efficient. There are three different reasons ionophore toxicity in pigs can occur: overdosing due to mixing errors, concurrent use of ethyl-ionophores with pleuromutiline class antibiotics (e.g. thiamuline), or feeding an ionophore intended for another species.

Toxicity occurs when the liver is unable to metabolize and excrete the ionophore. Pleuromutilins inhibit cytochrome P450 liver enzymes, which are needed for ionophore metabolism, resulting in ionophore accumulation and skeletal muscle damage (necrosis).

All ages except nursing piglets

• Affects skeletal and diaphragmatic muscle (does not usually affect cardiac muscle as seen in cattle and horses).
• High mortality.
• Respiratory distress.
• Ataxia.
• Lameness.
• Tremors.
• Hind limb weakness/paresis.
• Lower average daily gain.

• Overfeeding an ionophore due to mixing errors.
• Feeding ethyl ionophores concurrently with pleuromutalin antibiotics (e.g. tiamulin).
• Feeding an ionophore intended for a species other than pigs.

• Diagnosis can be quite difficult as the history and investigation must demonstrate an issue with the ionophore, either a mixing error or concurrent use with pleuromutalin antibiotic.
• Feed sample (current and previous) evaluation for presence of ionophore.
• Histopathology of skeletal and diaphragmatic muscle demonstrating muscle necrosis.
• Must rule out other diseases including vitamin and mineral deficiencies or toxicities

• If toxicity is suspected, all feed should be replaced immediately with new feed without antibiotics or ionophores. The recovery of the pig depends on the extent and duration of liver damage.
• If toxicity is suspected, immediately stop pleuromutalin use.
• Ensure correct dosage of ingredients in feed.
• Ensure pleuromutalin (e.g. tiamulin) antibiotics are never used while any ionophore is used in the feed. Veterinarians must always ask what feed antibiotics are being used before ever prescribing any new antibiotics.