Toxic plants are a concern in equine management as they pose health risks to horses when ingested. These plants contain various compounds that can lead to adverse effects ranging from mild discomfort to severe illness or death. Horses may encounter toxic plants in pastures, hay, or during foraging. Common toxic plants include ragwort, yew, and oleander, each containing specific toxins that affect equine physiology differently. Understanding the identification, distribution, and toxicological impact of these plants is important for prevention and management. This page compiles peer-reviewed research studies and scholarly articles that explore the identification, toxic mechanisms, and management strategies of toxic plants in relation to equine health.
James LF, Van Kampen KR, Staker GR.Of 70 Aberdeen-Angus cows which ate locoweed (Astragalus lentiginosus) during rotational grazing in Utah, because it was the only green feed available at the time, a large number aborted. All the cattle showed signs of poisoning, but recovered when removed from the pasture. There were signs of poisoning also in 12 horses, and though they seemed to recover signs of permanent damage to the central nervous system remained. Hereford cattle grazing plots with a similar proportion of locoweed were not affected, but for them other green herbage was available
Darby S, Sanchez LC, Mallicote MF, House AM, Plummer CE, Nadruz V, Benmoha RH, Roberts SM, Derendorf H, Silva-Sanchez C, Claire J, MacKay RJ.Creeping indigo (Indigofera spicata) toxicosis is an emerging problem among horses in Florida and bordering states. Objective: To quantify the putative toxins l-indospicine (IND) and 3-nitropropionic acid (NPA) in creeping indigo collected from multiple sites and to measure plasma toxin concentrations in ponies fed creeping indigo and horses with presumptive creeping indigo toxicosis. Methods: Experimental descriptive study with descriptive observational field investigation. Methods: Air-dried creeping indigo was assayed for IND and NPA content. Five ponies were fed chopped creeping indigo con...
Grabner A, Goldberg M.In a blind study serum and cerebrospinal fluid (CSF) of control horses and of horses in hepatic coma after chronic food intoxication with Senecio alpinus were collected simultaneously and the composition of free amino acids was determined. The hepatic encephalopathy index in serum (less than 1.65) and in CSF (less than 1.11) of liver patients was distinctly less than to the control values in serum (greater than 2.42) and in CSF (greater than 1.49). The serum concentrations of glutamic acid in hepatic coma were elevated five-fold in comparison to the controls. An indication of ammonia decontami...
Kern JR, Cardellina JH.Anemonin, the dilactone of cyclobutane-1,2-diol-1,2-diacrylic acid derived from the cyclodimerization of protoanemonin, a known blistering agent, was isolated from Clematis hirsutissima, a plant used by the Nez Perce and Teton Sioux nations as a horse stimulant.
Turner AS.Congenital and acquired torsion occur in the limbs of domestic animals. Congenital abnormalities are of clinical significance in foals; they are also seen in calves whose dams have ingested certain toxic plants that contain teratogenic agents. Acquired torsional deformities are most common in foals, but are also observed in adult horses, dogs, and llamas. Acquired rotational deformities are almost always associated with angular limb deformities. The clinical consequence of torsional deformities is the early development of degenerative joint disease.
Olson CT, Keller WC, Gerken DF, Reed SM.Of 10 horses in a heavily overgrazed pasture, 4 died within 1 week. Clinical signs included muscle tremors, ataxia, reluctance to walk, heavy sweating, and myoglobinuria. Serum creatine kinase, aspartate transaminase, and alkaline phosphatase activities were high. Histopathologic findings were nonspecific. On the basis of clinical signs, clinicopathologic findings, nonspecific histopathologic findings, the condition of the pasture, the identification of numerous white snakeroot plants from which trematone was extracted, and evidence that these plants had been heavily browsed, it was believed t...
Grant RC, Basson PA, Kidd AB.A paralytic condition of farm stock in South West Africa, characterized by prominent neuronal and some mild extraneuronal pigmentation, is described. The distribution of the pigment, which was mainly located in the larger neurones of the brain and spinal cord, is given. Experimental evidence, obtained by feeding the plant, is presented that the condition is caused by Trachyandra laxa var. laxa. The histochemical features of the pigment proved to be compatible with a lipofuscin.
Williams S, Scott P.Meal contaminated by Datura stramonium seeds at the rate of 0.5% by weight was fed to two horses. Both horses showed clinical signs of depression, anorexia, weight loss, rapid heart and respiration rates, mydriasis, polyuria, polydipsia and diarrhoea. Both recovered with treatment. Maize screenings contaminated by the seeds had been used in the manufacture of the meal.
Franken P, van Beukelen P, Blok G.Two horses became ill, and one died, after being fed onions, presumably over a long period. Their intake of grass was low at the time of illness because the pasture was covered with snow. Examination of blood and urine revealed signs of severe haemolytic anaemia.
Stegelmeier BL, Davis TZ.Range and pasture toxic plants can poison horses. Many of these plants are noxious weeds that can dominate plant populations and replace healthy forages. Poisoning is often difficult to diagnose as the resulting plant-induced disease is similar to other infectious, toxic, and nutritional diseases. Identifying potentially problem plants, and observing what plants horses are eating, is essential in determining the risk of poisoning. If the risk is significant, it can drive management to invest in strategies to avoid exposure, animal disease, and suffering.
Dewes HF, Lowe MD.Events leading to the deaths of two fillies at pasture are described. Pasture hay containing the flowering stages of Senecio jacobea (ragwort) had been fed three to four months earlier. Paddocks were subdivided with posts and rails treated with copper chrome arsenate. Six horses on the property chewed rails spasmodically. Both fillies presented with haemoglobinurea. Values in liver of 83 mg Cu kg and kidney 35 mg Cu kg wet weight and serum 1.4 mg Cu/l together with histophathology of seneciosis support a sequence of ragwort poisoning followed by copper accumulation in liver and kidney terminat...
Evans JW, Stanfield J, Hoffman LS, Slaussen C.Testes were obtained from 70 colts and stallions and were pooled according to age (4 months to 23 years) to determine the relationship of age to LH/hCG receptor kinetics. The receptor concentration (Rt) increased from 0.069 x 10(-11) M/mg crude membrane fraction (CMF) for the 4-14-month pools to 0.464 x 10(-11) M for the 2-3-year-old pools. A 10-fold increase in testicular size also occurred, and so the total number of receptors per testis was significantly increased. A further increase to 1.237 x 10(-11) M/mg CMF was observed for stallions older than 5 years. No differences in binding affinit...
Blanchard T, Fantinati M, Domange C, Priymenko N.The present report describes two novel cases of suspected intoxication with Galega officinalis in 6- and 21-year-old Arabian mares displaying acute respiratory signs. Both animals showed signs of pulmonary edema at physical examination, with the oldest of the two also manifesting severe dyspnea and foamy nasal discharge. The mares were grazing on the same meadow with hay available ad libitum. Botanical analysis of the latter showed traces of the toxic plant Galega officinalis (L.), which has been daily ingested at a dose of around 14 g of dry matter for three days. Based on the respiratory sig...
Rosenfeld G, Reichmann CE, Jaria LJ, Andrade SO.Hematological studies were developed on two mares and twelve adults castrate sheeps of "Ideal" breed. The animals had been on a pasture formed with Brachiaria radicans Napper for one and two months respectively. This experiment was developed in winter time, so the leaves of the graminea had a yellow-green color. Clinical and hematological observations were made weekly. The typical symptoms of intoxication failed to present as observed in the former investigation when the plant was green (3). The hematological exames showed only for ovines a slight anemia, it was also characterized as being mac...
Sloet van Oldruitenborgh-Oosterbaan MM, Schipper FC, Goehring LS, Gremmels JF.In the course of several days most of the 40 riding-school horses turned out in paddocks developed ataxia of variable severity. Five of these horses showed severe ataxia and tremors, became paralyzed and were euthanized. Eleven privately-owned horses which were stabled on the same premises showed no clinical signs. The most likely diagnosis seemed to be the 'neurological form of EHV1', although the signs were not entirely typical. A few weeks later a second outbreak occurred among the riding-school horses and one of the privately-owned horses also showed signs of ataxia. In the meantime it had...
Hurley DJ, Berghaus LJ, Hurley KA, Moore JN.To evaluate effects of black walnut extract (BWE) on equine mononuclear cells and determine whether BWE has direct proinflammatory effects. Methods: Mononuclear cells separated from blood samples from 8 horses. Methods: Aqueous BWE was prepared and processed to eliminate contamination with particulates and microbes. A Limulus amoebocyte lysate assay was used to detect lipopolysaccharide (LPS) contamination in the BWE. Mononuclear cells were incubated in minimal essential medium with or without the addition of 0.6% to 10% (vol/vol) BWE. These mononuclear cells were assessed for viability, activ...
Lotstra RJ, van den Broek J, Power T, Marr CM, Wijnberg ID.Atrial fibrillation is a common equine arrhythmia. Quinidine alone, or with digoxin are common treatments. Studies on outcome in Warmblood populations in which duration of the AF is often unknown are limited. Objective: To identify the factors that are associated with the success of full treatment cardioversion with oral medication, and establish whether there are differences in these factors between institutions. Methods: Retrospective case series using patient records of Equine University Clinic of Utrecht University and Rossdales Equine Hospital, Newmarket. Methods: Forty-nine horses treate...
Kellam LL, Johnson PJ, Kramer J, Keegan KG.Signs of mild colic, intermittent lethargy, and weight loss of 6 weeks' duration in a 2-year-old Quarter Horse gelding were attributed to persimmon (Diospyros virginiana) phytobezoar formation. Diagnosis of the phytobezoar was facilitated by gastric endoscopy. Signs of gastrointestinal tract obstruction were associated with a large phytobezoar in the lumen of the stomach, gastric ulceration, and obstruction of the small intestine (as a consequence of fragmentation of the primary bezoar). Conservative treatment, using mineral oil and dioctyl sodium sulfosuccinate, was unsuccessful. A celiotomy ...
Mello GW, Riet-Correa F, Batista MC, Carvalho CJ, Dias AC, Franklin FL, Silva SM, Dias A.Farmers in the State of Piauí in northeastern Brazil reported nervous signs in ruminants and donkeys after ingestion of Brunfelsia uniflora at the start of the rainy season when the plant is flowering. Leaves of the plant, collected at the start or at the end of the rainy season, were administered in single doses of 5-20 g/kg body weight to 8 sheep and 3 donkeys. Two sheep and 1 donkey that ingested 10 g/kg of the plant in November at the start of the rainy season, when the plant was flowering, developed severe convulsions and diarrhea. One sheep was euthanized and autopsied, and no significa...
González Medina S, Hyde C, Lovera I, Piercy RJ.Hypoglycin A (HGA) toxicity, following ingestion of material from certain plants, is linked to an acquired multiple acyl-CoA dehydrogenase deficiency known as atypical myopathy, a commonly fatal form of equine rhabdomyolysis seen worldwide. Whilst some plants are known to contain this toxin, little is known about its function or the mechanisms that lead to varied HGA concentrations between plants. Consequently, reliable tools to detect this amino acid in plant samples are needed. Analytical methods for HGA detection have previously been validated for the food industry, however, these technique...
Hertzsch R, Emmerich IU, Lachenmeier DW, Sproll C, Monakhova YB, Aboling S, Bachmann U, Vervuert I.Opioid alkaloids were identified in the urine of horses during an anti-doping control and in a case of intoxication. In both cases, it was suspected that the horses had ingested poppy-contaminated feed. To verify this suspicion, possible opioid alkaloid sources in Germany were identified through a literature research. Additionally, the contaminated feed was botanically and chemically analysed. The results indicated that both cases were most probably caused by the poppy in the feed. This highlights the previously underestimated risk of an intake of poppy-contaminated feed in horses. Recommendat...
Pearson EG.Of 41 equids referred to a veterinary teaching hospital in the Pacific northwest because of dyspnea and inspiratory noise, 3 ponies were diagnosed as having liver failure, most likely attributable to pyrrolizidine alkaloid toxicosis. Dyspnea appeared to be caused by laryngeal and/or pharyngeal paralysis. It is proposed that this paralysis was a manifestation of hepatic encephalopathy. Although these clinical signs are not common for pyrrolizidine toxicosis, practitioners should be aware of the possibility so that misdiagnosis of other causes of inspiratory dyspnea may not be made.
Botha CJ, Naudé TW.Well-known plant poisonings such as 'dunsiekte' (seneciosis) and 'jaagsiekte' (crotalariosis) of horses in southern Africa are briefly reviewed. Relatively unfamiliar mycotoxicoses such as stachybotryotoxicosis and perennial rye grass staggers and potentially occurring exotic intoxications such as equine nigropallidal encephalomalacia and ergot alkaloid poisoning are also discussed. This article is aimed at informing the southern African equine practitioner about probable poisonings that might occur locally in horses.
Votion DM, Habyarimana JA, Scippo ML, Richard EA, Marcillaud-Pitel C, Erpicum M, Gustin P.Equine atypical myopathy in Europe results from hypoglycin A (HGA) exposure through the ingestion of samaras or seedlings of the sycamore maple tree. This pilot study aimed at better defining sources of HGA intoxication in spring. Samaras fallen on the ground and then seedlings were collected at two-week intervals from sycamore, Norway, and field maple trees over the spring 2016. In early April, rainwater from wet seedlings collected after a rainy night was harvested to be analysed. Mid-May, samaras of the box elder, common ash, and inflorescences of sycamore maples were collected on the tree....
Wimmer-Scherr C, Taminiau B, Renaud B, van Loon G, Palmers K, Votion D, Amory H, Daube G, Cesarini C.Equine atypical myopathy (AM) is caused by hypoglycin A (HGA) and methylenecyclopropylglycine (MCPG) intoxication resulting from the ingestion of seeds or seedlings of some Acer tree species. Interestingly, not all horses pasturing in the same toxic environment develop signs of the disease. In other species, it has been shown that the intestinal microbiota has an impact on digestion, metabolism, immune stimulation and protection from disease. The objective of this study was to characterize and compare fecal microbiota of horses suffering from AM and healthy co-grazers. Furthermore, potential d...
Giles CJ.Five out of 20 horses (25 per cent) on one farm died from an acute hepatic encephalopathy typical of ragwort toxicosis. Circumstantial evidence implicated pasture rather than hay as the principal source of the toxic alkaloids. Plasma levels of gamma glutamyl transferase (GGT) were determined on three occasions in all surviving ragwort-exposed horses. Elevated GGT levels were a useful early indicator of hepatic damage although not all horses with this biochemical sign developed clinical disease.
Mueller C, Sroka L, Hass ML, Aboling S, These A, Vervuert I.Extensively used grasslands are frequently utilised for hay production for equines. Especially, extensive meadows have a great variety of plant species, which may include plants that are poisonous for equines such as meadow saffron (Colchicum autumnale L.). To authors' knowledge investigations about horses` avoidance behaviour towards dried meadow saffron in hay are missing. Reports of farmers are contrary to clinical symptoms described in case reports and associated with meadow saffron in hay. Objective: The aim of this study was to determine the rejection behaviour of horses for hay contamin...
Bochnia M, Ziegler J, Sander J, Uhlig A, Schaefer S, Vollstedt S, Glatter M, Abel S, Recknagel S, Schusser GF, Wensch-Dorendorf M, Zeyner A.Hypoglycin A (HGA) in seeds of Acer spp. is suspected to cause seasonal pasture myopathy in North America and equine atypical myopathy (AM) in Europe, fatal diseases in horses on pasture. In previous studies, this suspicion was substantiated by the correlation of seed HGA content with the concentrations of toxic metabolites in urine and serum (MCPA-conjugates) of affected horses. However, seed sampling was conducted after rather than during an outbreak of the disease. The aim of this study was to further confirm the causality between HGA occurrence and disease outbreak by seed sampling during ...
Fayrer-Hosken R, Stanley A, Hill N, Heusner G, Christian M, De La Fuente R, Baumann C, Jones L.The cellular effects of tall fescue grass-associated toxic ergot alkaloids on stallion sperm and colt testicular tissue were evaluated. This was a continuation of an initial experiment where the effects of toxic ergot alkaloids on the stallion spermiogram were investigated. The only spermiogram parameter in exposed stallions that was affected by the toxic ergot alkaloids was a decreased gel-free volume of the ejaculate. This study examined the effect of toxic ergot alkaloids on chilling and freezing of the stallion sperm cells. The effect of toxic ergot alkaloids on chilled extended sperm cell...
