Aflatoxin Poisoning in Horses: Recognising a Feed-Related Risk

By Dr Duncan Houston

A change in appetite, energy or weight can have many explanations in a horse. When several animals eating the same feed become unwell, or feed has been damaged during storage, a toxin investigation may form part of the veterinary work-up.

Aflatoxins are poisons produced by certain Aspergillus moulds. They can contaminate ingredients before harvest or during storage, and their effects on the liver mean that a suspect batch deserves careful handling even when it does not look dramatically mouldy.

Quick Answer

Aflatoxin poisoning is a possible cause of liver injury in horses exposed to contaminated feed. Stop using the suspect batch, retain labelled samples and contact your veterinarian if exposure or illness is suspected. There is no specific antidote, and neither appearance nor smell can reliably confirm that feed is safe.

How feed becomes contaminated

Aspergillus species can produce aflatoxins in susceptible crops and stored ingredients, including maize and some oilseed products. Crop stress, heat and moisture can influence contamination, but the presence of mould does not identify which toxin is present. Conversely, toxin may remain in material without obvious visible mould.

The Merck Veterinary Manual’s aflatoxicosis review describes liver damage, impaired clotting and variable susceptibility between species. Many published feed limits and treatment studies concern livestock other than horses. They should not be converted into a supposedly safe dose for an individual horse.

Signs that deserve veterinary attention

Possible signs include reduced appetite, lethargy, weight loss, jaundice and unusual bleeding. More severe liver dysfunction can lead to altered behaviour, disorientation or incoordination. These findings are not specific to aflatoxins, and an affected horse may have a different liver disease or another feed-associated illness.

Immediate steps after a suspected exposure

1. Stop feeding the suspect material to every horse with access to it. Prevent accidental use by clearly marking and separating the batch.
2. Call your veterinarian with the product name, batch number, purchase date, storage conditions and approximate feeding amounts.
3. Keep packaging and representative samples. Ask the vet or testing laboratory how much to collect, where to sample and how to store it.
4. List all exposed animals and record appetite, manure, behaviour and any treatment already given.
5. Discuss a suitable replacement ration. Provide clean water and safe forage as advised, without making unnecessary abrupt concentrate changes.

Do not mix suspect feed into clean feed to dilute it, sell it on or feed it to another species. Contact the supplier with the batch details and veterinary concerns. Keep enough material for investigation before arranging disposal.

Emergency care and veterinary diagnosis

A horse showing neurological signs, spontaneous bleeding or profound weakness needs urgent help. Keep the area quiet and avoid forcing the horse into a trailer before speaking to the vet. Do not drench an uncoordinated horse or give human medicines.

Blood tests help assess liver injury and function, clotting, hydration and other organ changes. Ultrasound or a liver biopsy may be considered when appropriate; bleeding risk affects that decision. Feed analysis can identify toxins, but sampling matters because contamination may be uneven within a bag or delivery.

Treatment centres on removing the exposure and supporting the horse’s circulation, nutrition and complications. The Merck owner guide to equine liver disorders explains why management depends on the underlying disease and the degree of lost liver function. A raised liver enzyme alone does not establish aflatoxin poisoning or predict recovery.

Other problems that can look similar

Other toxic plants, infections, inflammatory liver disease and medicine-related injury can cause liver abnormalities. Fumonisins are different feed-associated toxins that can cause severe neurological disease in horses. A laboratory and clinical investigation should therefore consider the actual ingredients and signs rather than assuming every mould exposure is aflatoxin poisoning.

Common mistakes to avoid

• Removing visible mould and feeding the remainder.
• Using a negative result from an unrepresentative handful as proof the entire batch is safe.
• Applying poultry or cattle toxin thresholds to horses.
• Relying on a supplement or commercial binder as an antidote.
• Discarding all packaging and feed before samples can be taken.

Reducing future risk

Buy traceable feed, keep it dry and protected from pests, rotate stock and follow storage instructions. Inspect bins, bags and deliveries for water damage and heating. Clean containers between batches rather than continually topping them up. Good storage reduces risk but cannot remove toxins already present when feed arrives.

Frequently asked questions

Does mouldy feed always contain aflatoxin?

No. Different moulds and toxins are possible, and visible mould alone cannot identify the cause.

Will a toxin binder protect my horse?

Do not assume so. Evidence varies by product, toxin and species; it cannot replace withdrawal of contaminated feed and veterinary care.

Can affected horses recover?

Some can, but the outlook depends on the exposure and severity of liver injury. Follow-up testing helps assess progress.

A clear feeding history and carefully preserved samples give your veterinarian the best chance of connecting illness with a feed problem and protecting other horses.

For help understanding your animal’s care and preparing questions for your veterinarian, visit ASK A VET™.