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What is Dwarf Larkspur Poisoning?

Delphiniums, or larkspur, is a deceptively beautiful plant predominantly found west of the Mississippi River. Dwarf larkspur primarily grows in the mountains and lower piedmont region of North Carolina, Mississippi, Tennessee, Kentucky, and West Virginia. Known for its bluish-purple color, larkspur is the second-leading cause of livestock loss, costing farmers tens of thousands of dollars annually. Poisonings occur predominantly in cattle during late spring and early fall when plant toxicity is at its highest level. There are two major groups of the plant, separated only by its growth characteristics and patterns. Both types are poisonous to livestock and humans. Dwarf larkspur (or low larkspur) grows wildly across pastures and grasslands. It may also be found in ravines, alongside streams, and in other moist woodlands. Unlike its counterpart, Tall larkspur, low delphiniums grow no bigger than three feet in height, while the other may reach to heights of eight feet. Due to its beauty, the plant is found in gardens across the United States.

The toxicity of the garden perennial, larkspur, is mostly unknown outside of veterinary and farming circles. On the scale of poisonous plants and grasses, dwarf larkspur is mild to moderate. Its toxins include D. nelsonii, D. geyeri, D. virescens, and D. bicolor, and function as potent neuromuscular blocking agents. To avoid instances of plant poisoning, pasture management is recommended. Horses may accidentally ingest small leaves and pieces of toxic plants if mixed with their usual grazing, hay and feed. If concerned, have hay inspected for possible contamination.

Dwarf larkspur (or low larkspur) is a deceptively beautiful bluish-purple plant that is the second-leading cause of death in livestock, particularly cattle.

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Symptoms of Dwarf Larkspur Poisoning in Horses

  • Staggering
  • Falling
  • Seizures
  • Bloat
  • Arrhythmia
  • Constipation
  • Increased salivation
  • Muscle quivers
  • Convulsions
  • Falling with head downhill
  • Heart/lung failure
  • Death

Causes of Dwarf Larkspur Poisoning in Horses

Like most toxic weeds, horses may sample dwarf larkspur, but typically do not choose to eat the plant due to its strong, acrid taste and smell. Under normal conditions, a healthy, well-fed horse with ample grazing will ignore the plant, along with the other noxious plants in the pasture. During drought or other times when food is not available, horses will graze on larkspur and other poisonous plants.

Diagnosis of Dwarf Larkspur Poisoning in Horses

Plant poisoning in its milder forms is difficult to diagnose due to its having generalized symptoms. Gastrointestinal symptoms like constipation will resemble a wide range of conditions. In its most severe forms, diagnosis may occur post-mortem after sudden death. Veterinarians will also recognize symptoms due to repeated regional poisonings. If consumed in small amounts, it shouldn’t have any effect on a large-bodied animal like a horse or cow. In large amounts, the plant may cause a rapid fatality. Cattle have been fatally poisoned by larkspur within 1-4 hours. The veterinarian may choose to walk the pasture and paddocks in the case of suspicion of poisoning; identification of the plant and other noxious weeds on the property can lead to a diagnosis.

Treatment of Dwarf Larkspur Poisoning in Horses

Signs of larkspur poisoning in both horses and cattle are related to the central nervous system, including mild muscle tremors, stiffness, weakness, hyper-irritability, confusion, and collapse. Both horses and cattle may also experience gastrointestinal symptoms including constipation and bloat. Cardiovascular conditions include hypotension, myocardial depression, and arrhythmias. Pneumonia may occur as a secondary complication. Fatalities typically occur due to respiratory paralysis or by falling into a recumbent position head first. 

In the rare situation when the consumption of larkspur is observed, veterinary treatment must occur immediately. The horse will be administered activated charcoal and magnesium sulfate. Physostigmine, a drug used to halt further damage to the central nervous system, is occasionally used to treat poisoning by certain plants such as nightshade and dwarf larkspur. Physostigmine is effective as a treatment if given within an hour of larkspur poisoning, and repeated as indicated by the veterinarian. Many veterinarians use the drug only in life-threatening cases due to its potentially harmful side effects. Particularly in the case of cattle, treatment is futile as sudden fatality often occurs.

Recovery of Dwarf Larkspur Poisoning in Horses

Though it is possible to control larkspur with herbicides, using chemicals is cost-prohibitive in most cases. Spraying particularly concentrated areas may be effective in reducing opportunities for grazing. Pasture management is key to avoiding plant and grass poisoning. Walking the area must be done on a constant basis in order to spot potentially noxious weeds or foreign growth. Samples should be taken in the case of unfamiliar plants. Veterinarians should be able to determine the type of plant and whether there is a chance for poisoning.