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What is Dodder Poisoning?

Belonging to the morning glory family, the many species of Cuscuta are leafless, rootless, parasitic plants with thread-like stems that coil around and attach to host plants. Dodders lack chlorophyll, which is why they penetrate the tissues of host plants and steal their nutrients. Stems can range in color from white, to yellow and orange, and even to purple. Dodder bears small clusters of flowers in white, pink, or yellow in the summer months.

Dodder can cover several square feet if it finds a suitable host, producing thousands of seeds that can remain dormant in the ground for many years. Seeds form filaments that elongate to find a host in pastures, fields, and wherever else the hosts it prefers grows. There are many species native throughout North America.

Dodder, also referred to as strangleweed, is a parasitic-type plant that feeds on other plants, such as clovers and alfalfa. Not only can it destroy a field of alfalfa, but when ingested, dodder can cause problems in your horse’s digestive and nervous systems, resulting in weight loss, abdominal pain, unusual behavior, and significant brain damage that can be fatal.

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Symptoms of Dodder Poisoning in Horses

Symptoms of a dodder poisoning can vary, as dodder can absorb toxins from the plants it feeds from. Many of these toxins can affect the liver and nervous system. Some of the more common signs include:

  • Diarrhea
  • Decrease or loss of appetite
  • Weight loss
  • Colic
  • Abdominal pain 
  • Depression
  • Weakness
  • Abnormal behavior
  • Muscle tremors
  • Incoordination
  • Staggering
  • Wander aimlessly
  • Lying down
  • Coma
  • Convulsions
  • Death 

Types

There are many types of dodder within the species. Many are named after the plants they parasitize. Some common dodder species include:

  • Cuscuta breviflora, Chaparral dodder
  • Cuscuta campestris, Golden dodder 
  • Cuscuta coryli , Hazel dodder
  • Cuscuta epithymum, Alfalfa dodder 
  • Cuscuta gronovii, Common dodder
  • Cuscuta indecora, Collared dodder
  • Cuscuta japonica, Japanese dodder 
  • Cuscuta pentagona, Field dodder

Causes of Dodder Poisoning in Horses

Research has not yet identified the exact toxins that occur naturally in dodder, but they seem to affect the digestive and nervous systems, as well as the liver. This can result in liver damage, hemorrhages seen throughout the body, and brain damage that can cause the affected horse’s behavior to become unpredictable. The toxic effects of dodder can become more complicated due to the fact that dodder absorbs toxins from the host plants it feeds from. Since there is a wide range of host plants the parasitic dodder attaches to, there are many possible toxins that could be involved in a dodder poisoning of your horse.

While dodder can be consumed in fields and pastures, it is often rolled into hay bales. Poisoning from contaminated hay is usually seen after ingestion has taken place over several weeks. Symptoms are more often seen when dodder makes up about half of the hay in the bale.

Diagnosis of Dodder Poisoning in Horses

A diagnosis of dodder poisoning can be difficult. If you have seen evidence that your horse has ingested this plant, bring in a sample of the dodder, along with the plant it is parasitizing, to your veterinarian to be correctly identified. Diagnosis is then based on plant identification and symptoms.

If you do not know your horse has ingested this plant, your veterinarian will need to examine your horse and run a series of tests to find a cause to the symptoms. Blood samples will be taken for a CBC, serum analysis, and other tests. A urinalysis may also be taken. Often, these tests can reveal the presence of alkaloids and other toxins, leading to a plant or chemical poisoning. 

Treatment of Dodder Poisoning in Horses

There is no specific treatment for dodder poisoning. Removing the source of dodder, whether in pastures or baled with hay, has been seen to resolve symptoms within days, without further treatments. Treatment can help to reduce absorption of toxins, often through the administration of activated charcoal or mineral oil. Supportive treatment can be given, such as fluid and electrolyte therapies. 

Other treatments aimed at addressing the various symptoms that could be present will be specific to any alkaloids found, host plants identified, or particular symptoms present, and will be prescribed on a case by case basis.

Recovery of Dodder Poisoning in Horses

Recovery is generally good in cases of many dodder toxicities. Often, simply removing the toxic plant from your horse’s grazing and feeding areas can resolve symptoms within 3 days. The severity of your horse’s condition does depend on other factors, such as the added toxins absorbed by the dodder from the host plant. Due to the various toxins that could be present in the hosts, a prognosis of recovery will depend on your horse’s specific case.  Prevent your horse from ingesting dodder by practicing good management strategies, such as:

  • Regularly monitor dodder growth on your property
  • Destroy dodder through mowing, burning, and herbicides
  • Refrain from hand pulling dodder off of host plants, as any stems left behind can continue to grow
  • Clean all equipment used in removal thoroughly
  • Regularly inspect hay for signs of dodder