Botulism in Donkeys: Feed-Related Toxin Exposure and Progressive Paralysis

Botulism is a severe poisoning caused by a nerve toxin made by Clostridium botulinum. In adult equids, including donkeys, it is most often linked to eating preformed toxin in spoiled forage or feed rather than a contagious infection. The toxin blocks communication between nerves and muscles, causing a flaccid, progressive paralysis that can become fatal if the muscles used for swallowing or breathing are affected.

Although published donkey-specific studies are limited, donkeys are managed as equids and your vet will usually apply horse-based evidence to diagnosis and treatment. In horses, botulism is uncommon but highly serious, and even very small amounts of toxin can cause disease. Feed-related cases are often called forage poisoning.

Many pet parents first notice vague weakness, a sleepy expression, or trouble eating. As the toxin spreads, affected donkeys may have poor tongue tone, drooling, difficulty swallowing, reduced tail or eyelid tone, and increasing trouble standing or walking. This is why any suspected case should be treated as an emergency.

In adult donkeys, the most likely cause is feed-related toxin exposure. Clostridium botulinum grows best in low-oxygen, decaying material. That means risk rises when forage or feed is spoiled, improperly fermented, stored wet, or contaminated with decomposing animal tissue. A small bird, rodent, or other carcass accidentally baled into hay or mixed into feed can create enough toxin to make an equid critically ill.

High-risk feeds include moldy hay, poorly stored grain, haylage or silage, and round bales with wet, damaged, or anaerobic areas. Horse-based guidance also notes regional risk differences, with type B botulism more recognized in parts of the eastern United States and type C often linked to carcass contamination. Donkeys on pasture with supplemental round bales or stored forage can face the same exposure risks.

Less commonly, botulism can develop from a contaminated wound or from toxin production in the intestinal tract after ingesting spores. Those forms are discussed more often in foals than in adults. Still, if your donkey has a deep wound plus weakness or swallowing trouble, your vet may keep wound botulism on the list of possibilities.

Diagnosis is usually based on a combination of history, physical exam, and pattern of neurologic signs. Your vet will look closely at swallowing ability, tongue tone, eyelid and tail tone, gait, and whether weakness is getting worse. A recent history of suspicious hay, haylage, silage, round bales, or possible carcass contamination can be a major clue.

There is no single perfect test that rules botulism in or out right away. Depending on the case, your vet may submit serum, feces, stomach or intestinal contents, wound samples, or suspect feed for toxin testing, PCR, or other specialized assays. In equids, these tests can be helpful, but false negatives happen because toxin levels may be very low or unevenly distributed.

Your vet will also work to rule out other causes of weakness or paralysis, such as severe electrolyte problems, toxic plants or chemicals, trauma, choke with secondary complications, tick paralysis, or other neurologic disease. Because treatment works best early, your vet may recommend starting supportive care and pursuing presumptive treatment before test results are back.

Prevention centers on feed quality and storage. Check hay, grain, and bagged feed before every feeding. Discard forage that smells rotten, feels hot or slimy, looks moldy, has wet pockets, or may contain animal remains. Be especially cautious with round bales, haylage, and silage, because low-oxygen areas can support toxin production if storage conditions are poor.

Store feed in a dry, clean area and protect it from moisture, rodents, birds, and wildlife. Remove carcasses promptly from barns, paddocks, and feed storage spaces. If one donkey becomes ill after eating a particular batch of forage, stop feeding that lot to all equids until your vet advises you. Saving a sample of the suspect feed can help with investigation.

Vaccination may be worth discussing with your vet in higher-risk regions or on farms using higher-risk forage systems. In the United States, the licensed equine botulism vaccine targets type B and is considered risk-based rather than routine for every equid. Because donkey-specific vaccine protocols are not as well studied, your vet can help decide whether a horse-based protocol makes sense for your herd, geography, and feeding practices.