EQUINE VETERINARY EDUCATION / AE / MAY 2015


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Datura stramonium (jimson weed) Jimson weed is a plant from the Solanaceae family characterised by its malodorous leaves, large tubular flowers and ovoid spiny fruit capsules. Jimson weed may be grown as an ornamental plant or found as a weed across Europe (Anadón et al. 2012). The plant is entirely toxic and contains tropane alkaloids which possess strong anticholinergic properties (Soler-Rodríguez et al. 2006). Because Jimson weed is rarely consumed by horses in the pasture due to poor palatability, poisoning usually occurs when the plant contaminates hay (Naidoo 2012). Toxicity in horses usually results soon after ingestion and is related to the amount ingested and the alkaloid concentration (Naidoo 2012). Common clinical signs include tachycardia, mydriasis, dry mucosae and convulsions, but severe, intractable impaction colic is the predominant sign of horse intoxication (Botha and Naudé 2002; Naidoo 2012). In an equine centre in Toledo, Spain, a jimson weed


poisoning episode occurred as a result of ingestion of hay grossly contaminated (up to 51% by weight) with the prickly fruit and stem of the plant. Colic was the most remarkable clinical sign observed in affected horses and one horse died from acute gastric dilatation and rupture (Soler-Rodríguez et al. 2006). In Bulgaria, an outbreak of jimson weed poisoning involving 34 horses after ingestion of harvested ensiled corn heavily contaminated with freshly cut jimson weed, was reported (Binev et al. 2006a). Clinical signs included mild hyperthermia, mydriasis, dry mucosae, tachycardia, polypnoea, dyspnoea, acute gastric distention and severe intestinal gas accumulation due to adynamic ileus, anorexia, lack of defaecation, thirst and urination (Binev et al. 2006a). Specific haematological changes such as


hyperchromaemia, erythrocytosis, increased haematocrit value and low erythrocyte sedimentation rate were observed and a normalisation of these parameters within 4–5 days of exposure was indicative of the favourable issue of intoxication (Binev et al. 2006b). Post mortem analysis revealed toxic liver dystrophy and extensive dystrophic and necrotic changes in the kidneys and myocardium (Binev et al. 2006a).


Taxus baccata (European yew) European yew (Fig 3) is an evergreen tree or shrub from the Taxaceae family found across much of Europe. In France and


Belgium, European yew is the most significant poisonous plant for horses (Chandes 2002; Berny et al. 2010; Vandenbroucke et al. 2010) and cases have also been recorded in Italy (Caloni et al. 2013) and Switzerland (Curti et al. 2009). With the exception of the fleshy red aril around the seed, all parts of the plant contain taxine alkaloids and are extremely poisonous. Irritant volatile oils are also found throughout the plant (Anadón et al. 2012). Taxine alkaloids are cardiotoxic and capable of causing hypotension, bradycardia and depressed atrioventricular conduction (Anadón et al. 2012). Horses are suspected to be the most susceptible species to European yew toxicosis. Ingestion of 200–400 mg/kg bwt of yew leaves has been reported to be the minimum lethal dose for horses (Ogden 1988; Tiwary et al. 2005; Wilson and Hooser 2012). Clinical signs of poisoning include nervousness, trembling, dyspnoea resulting from severe colitis, ataxia, diarrhoea, bradycardia, convulsions and collapse, but sudden death (24 h or less depending on the amount ingested) due to acute cardiac arrest is usually the most common result (Tiwary et al. 2005; Anadón et al. 2012).


Toxalbumin-containing plants


Robinia pseudoacacia (black locust) Black locust (Fig 4) is a fast-growing deciduous tree from the Fabaceae family, native to North America, but widely cultivated and naturalised in Europe. Horses are the animals most susceptible to the effects of black locust (Vanschandevijl et al. 2010). Poisoning may result from the ingestion of roots, bark, sprouts, seeds and pods (Anadón et al. 2012). The primary toxic principle is the toxalbumin robin (Botha and Naudé 2002). The glycoside robitin and alkaloid robinine are also found throughout the plant (Vanschandevijl et al. 2010). Clinical signs usually develop 1–2 h after ingestion and seem to be dose-dependent as small amounts lead to a gastrointestinal upset and higher doses cause CNS signs (hyperexcitability) to appear (Uhlig et al. 2008; Vanschandevijl et al. 2010). The following clinical signs have been reported: anorexia, lethargy, abdominal pain, diarrhoea (which may be bloody) or dark and firm faeces, laminitis, weakness to posterior paralysis, head pressing and absence of menace response and pupil reflexes (Botha and Naudé 2002; Uhlig


Fig 3: Taxus baccata (European yew). Photograph by C. Cortinovis.


Fig 4: Robinia pseudoacacia (black locust). Photograph by C. Cortinovis.


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