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What is Holly Poisoning?

Holly, also known as Ilex, is a member of the family Aquifoliaceae. There are about 400 species of these plants. It is an evergreen tree or large shrub that is conical or oval-shaped. 

Holly can be seen in the wild and is also used for landscaping and as a screen. The branches and berries of the holly are used for decorations during the holidays.

The leaves of the holly are elliptical to oval in shape and are glossy and medium to dark green in color. Sections of the leaves can have spine tips. Leaves of the holly do not fall off during the autumn season. The bark of the holly is either light gray and smooth or dark gray and mottled. The holly produces flowers that vary by the species, showing up in the spring, as well as small fruit in the fall or winter. The fruit are berries that grow in clusters and can be bright red, purple or black.

While horses typically are uninterested in eating holly, during drought conditions they may ingest it; unfortunately the berries and leaves of the holly can be toxic to your horse.

A member of the family Aquifoliaceae, and including around 400 species, holly is toxic in horses, causing symptoms like gastrointestinal upset, difficulty swallowing and convulsions.

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Symptoms of Holly Poisoning in Horses

Should your horse ingest holly, you will likely see the following:

  • Gastrointestinal upset
  • Diarrhea
  • Depression
  • Trouble swallowing
  • Blurry vision
  • Irregular heartbeat
  • Convulsions

Types 

There are about 400 species of holly in the family Aquifoliaceae. These include:

  • English holly (I. aquifolium) - A tree that grows to almost 50 feet and has spiny, shiny, dark evergreen leaves and red fruit
  • American holly (I. opaca) - Grows taller than the English holly and has oblong, prickly leaves and red fruit. There are also yellow fruited forms
  • Chinese holly (I. cornuta) - From East Asia, this is a shrub that grows to 10 feet, generates scarlet berries and shiny evergreen leaves
  • Japanese holly (I. crenata) -From East Asia, this is a shrub growing to 20 feet that has small, evergreen leaves and black berries
  • Yaupon (I. vomitoria) - Native to eastern North America, it is a shrubby tree that grows to 26 feet and has oval leaves and red berries
  • Possum haw (I. decidua) - A deciduous shrub with red fruit that grows to 33 feet
  • Yerba mate (I. paraguariensis) An evergreen shrub from South America, it grows to 21 feet and its leaves are used to make tea

Causes of Holly Poisoning in Horses

The berries of the holly are toxic to horses when consumed. The toxins contained in the berries include saponins, terpenoids, sterols, alkaloids and cyanogenic glucosides. How high the concentration, as well as the types of toxins present will depend on the stage of growth. As the fruits ripen, the level of saponins decreases, but the concentration of tannins increases. Ilicin is present in holly and is toxic to the digestive system, nervous system and cardiovascular system. Toxicity from the leaves and berries is typically low.

Diagnosis of Holly Poisoning in Horses

Should your horse ingest holly, he may show immediate discomfort resulting from any spikes on the leaves eaten. Depending on how much was eaten, your horse may experience gastrointestinal symptoms. Should you notice that your horse has consumed holly, or observe symptoms that point to something being amiss, you will want to contact your veterinarian, who can conduct a physical examination of your horse. 

If you saw him eat the holly or suspect he may have, it is a good idea have a piece of the tree available at the examination as it may help your veterinarian in diagnosing your horse. Your veterinarian will ask you about your horse’s grazing as well as for information on their diet and any supplements or medications they are currently taking. A complete blood count, biochemistry profile and urinalysis will likely be done to make sure that there is nothing else going on with your horse that is leading to his symptoms.

Treatment of Holly Poisoning in Horses

Treatment will depend upon how long it has been since the plant was consumed. Your veterinarian may suggest that you put your horse in a quiet stall to reduce anxiety and confusion. He may administer activated charcoal if he feels that a binding of the toxins is necessary. The veterinarian will examine your equine’s mouth to see if residual plant material is found. It is important that water is available for your horse to ease the pain he feels in his mouth and so that he can replace fluids that were lost during diarrhea. 

In more severe cases, your veterinarian will provide supportive therapy in the form of oral intravenous fluids and repeat the activated charcoal if needed. Your veterinarian may monitor your horse’s heart and may recommend anti-inflammatory medication to reduce the swelling he is experiencing. In some cases, hospitalization may be necessary. Fortunately, due to the spiny texture of the holly plant most horses will avoid it unless no other forage is available.

Recovery of Holly Poisoning in Horses

It is important to remove the holly from the area where your horse is grazing to avoid a recurrence of the poisoning. Make sure to provide your horse access to plenty of clean water as he is recovering from his symptoms to ensure that he does not get dehydrated. It is best to follow the recommendations of your veterinarian and attend follow-up appointments as requested to ensure the best outcome for your horse. Your veterinarian can assist you in identifying potentially noxious plants that may be on your property.