What is Kimberley Disease?
Sheep and goats may be affected; however, horses are 30 times more susceptible to suffering from this toxicity.
Poisoning from this plant often causes nervous system symptoms such as ataxia, head pressing, and aimless walking, hence the name walk-about disease. This can occur following the ingestion of large amounts of the plant; in these cases, the progression of the disease is acute. In some cases, low levels of exposure may cause cumulative liver damage, with symptoms developing over a year. As there is no cure for Kimberley disease in horses, prevention is essential for the health of your horse.
Kimberley, or walk-about disease, is named after the district in the Northern Territory of Western Australia where horse poisonings most often occur. This condition occurs following the ingestion of plants of the Crotalaria species. These plants have the potential to be toxic to horses due to the cumulative damage they cause on the liver.
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Symptoms of Kimberley Disease in Horses
The symptoms experienced by your horse may have an acute onset if a large amount is consumed. These symptoms include:
- Nervous system damage and head pressing
- Abnormal or erratic behaviour
- Weight loss and anorexia
- Lack of control of the hind quarters or dragging of the hind legs, causing worn tips of the hooves
- Red or copper colored urine
- Difficulty swallowing
- Aimless wandering or walking in circles
Causes of Kimberley Disease in Horses
Kimberley disease is caused following the ingestion of plants of the genus Crotalaria. The species of this plant that are known to cause Kimberley disease in horses are:
- Crotalaria crispata
- C. novae-hollandiae
- C. ramosissima
- C. retusa
- C. dissitiflora
- C. trifoliastrum
The cause of toxicity in these plants is the presence of substances called pyrrolizidine alkaloids (PAs). Following ingestion these poisons travel to the liver and are metabolized into pyrroles. These metabolites are toxic to the liver and cause the healthy liver cells to be replaced by fibrous liver tissue. In many cases, repeated intermittent access to these plants causes cumulative damage over time, leading to liver failure. Although ingestion of large volumes may cause acute symptoms, in some cases the onset of disease may be slow, taking up to 18 months.
Diagnosis of Kimberley Disease in Horses
The first thing your veterinarian will do is perform a thorough physical examination. Your vet will ask questions and discuss your horse’s history with you. It is important to let your vet know if your horse has had access to this plant or if other animals are showing similar or unusual symptoms.
Your veterinarian will then watch your horse from a distance to observe their gait and movement, behaviour and body condition. Symptoms such as head pressing, ataxia or aimless walking which are characteristics of this disease may suggest Kimberley disease to your vet.
Your vet will carefully examine your horse, monitoring heart and respiration rates and thoroughly checking over the body. A urinalysis may be taken which on visual examination may show red or copper coloring.
Often, a presumptuous diagnosis can be made from your horse’s clinical signs. Your veterinarian may choose to perform a blood chemistry or liver test; this may show evidence of the metabolites of PAs, however, only if consumption has occurred recently. In cases of fatalities due to poisoning, the liver will often show changes and damage that enable diagnosis.
Treatment of Kimberley Disease in Horses
Unfortunately, for animals affected by the ingestion of large amounts of the plant causing Kimberley disease there is no cure. Euthanasia may be considered for humane reasons. Even with consumption of a small portion of the plant, if it is cumulative over time, liver damage can result. Often, by the time symptoms are noted, the toxicity has progressed to dangerous levels. Therefore, prevention is the best option for your horse.
Recovery of Kimberley Disease in Horses
The plant that causes Kimberley disease is not palatable to horses, and therefore is very rarely ingested in horses that are provided with adequate feed. Ensuring adequate feed is available to your horse at all times will reduce the chance of ingestion due to indiscriminate grazing. If grazing is limited remove your horse from pastures with plants of the Crotalaria species and feed high quality hay and feed.
In some cases, accidental ingestion may occur due to contamination. To reduce this risk of accidental ingestion, ensure that your horse’s food is obtained from a reliable source. Regularly clean and check to ensure that machinery, seed and hay are free of contamination. As seeds may be present in stools, quarantine new livestock for at least four days prior to introducing to the property to allow ingested seeds to be excreted.
Remove all plants of the Crotalaria species either mechanically or using appropriate pesticides from the pastures of your horses or livestock. Discuss safe options with your veterinarian.
Amino acids and other dietary supplements and support may be given to horses that suffer from liver damage due to ingestion of the Crotalaria plants.