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What is Caley Pea Poisoning?

Also known as singletary or rough pea, the caley pea is a legume with characteristic leaves made of two long leaflets that end in coiled tendrils that can grow up to 40 inches long. In spring, small flowers bloom in shades of reds and blues. Distinctively hairy, flat, and oblong seedpods turn from green to brown when readying to release their seeds. Caley pea can be found in places with dry or moist soils, from roadsides, pastures and fields, to wetlands and rocky shores.

Ingestion of the caley pea plant, or Lathyrus hirsutus, can cause neurological symptoms in your horse, from incoordination to paralysis that can affect several areas of the body. Lathyrism is a syndrome that can result from chronic consumption of the seeds of the caley pea, which often occurs accidentally with hay.

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Symptoms of Caley Pea Poisoning in Horses

Symptoms of a caley pea poisoning reflect conditions of paralysis, and can include staggering, incoordination, and roaring, a condition resulting from a paralyzed laryngeal nerve. If not treated quickly, roaring can progress to a fatal asphyxiation. While symptoms can be seen within days of consumption, they can also take months to appear. Signs include:

  • Paralysis of the rear legs
  • Roaring 
  • Sweating 
  • Lethargy 
  • Fast, weak pulse
  • Difficulty breathing
  • Head pressing 
  • Shortened stride 
  • Abnormal or stilted gait 
  • Uncoordinated gait 
  • Staggering 
  • Muscle atrophy 
  • Muscle tremors 
  • Weight shifting
  • Swaying the hindquarters
  • Abnormal stance 
  • Falling down
  • Inability to rise
  • Seizures
  • Death from asphyxiation 
  • Osteolathyrism

Causes of Caley Pea Poisoning in Horses

Caley pea poisoning occurs from the ingestion of the seeds of the caley pea, which often occurs when horses eat hay that contains them. Caley pea can also be eaten in the pasture, especially when there is a lack of other green forage, and can increase in toxicity during drought conditions. While generally non-toxic for most mammals, horses are particularly susceptible to the amino acids within the seeds. 

These amino acids include beta-aminopropionitrile (BAPN), which has been linked to osteolathyrism, a syndrome characterized by skeletal deformities and a ruptured aorta, L-alpha gamma-diaminobutyric acid, and beta-N-oxalylamino-L-alanine (BOAA), which affects the neurological system. Besides phenol and glycosides, caley pea also contains high levels of selenium, which has been linked to lathyrism.

Diagnosis of Caley Pea Poisoning in Horses

Diagnosis of a caley pea poisoning is based on evidence of plant consumption and symptoms seen in your horse. Bring in a sample of the plant your horse has been eating to your veterinarian to positively identify. If you have not seen any evidence of plant ingestion, your veterinarian will need to run tests to determine the cause of your horse’s symptoms.

Tests that often follow a physical exam can include blood and serum testing, which can often reveal the presence of toxins. This alone may lead your veterinarian to a diagnosis of a plant poisoning. X-rays, ultrasounds and other imaging techniques may be used to ensure there is not a mass or any internal damage causing your horse’s symptoms. Seeds can also be detected in hay with a microscopic examination.

Treatment of Caley Pea Poisoning in Horses

Treatment for caley pea poisoning begins with removing the plant from your horse’s reach. This can be plants in the pasture or along any fence lines, or any hay that has been contaminated with its seeds. Your veterinarian may change your horse’s diet. Ascorbic acid as an antidote may be added.

If your horse has been severely poisoned with a large ingestion of caley pea seeds at one time, activated charcoal may be administered to reduce toxin absorption. Supportive care may also be given, often in the form of fluid and electrolyte therapy.

Recovery of Caley Pea Poisoning in Horses

Recovery from a caley pea poisoning depends on your horse’s condition, the amount of seeds consumed, and the duration that caley pea seeds have been eaten. If treatment is administered quickly, or if symptoms are mild, your horse may recover. In more severe cases where a larger amount of seeds has been eaten, your horse may experience seizures or paralysis. Recovery after these symptoms have occurred is poor. If consumption has been chronic, and lathyrism or osteolathyrism have occurred, your horse may recover with some permanent damage.

Prevention of a caley pea ingestion involves monitoring and removing caley pea wherever it is found on your property. Be sure to inspect your horse’s hay for signs of caley pea seedpods, and always provide quality green forage.