Poisoning in horses refers to the ingestion, inhalation, or absorption of toxic substances that can adversely affect their health. These substances may include plants, chemicals, medications, or environmental toxins. Poisoning can lead to a range of clinical signs, from mild gastrointestinal upset to severe neurological or systemic effects, depending on the toxin involved. Common toxic substances for horses include certain plants like oleander and yew, heavy metals such as lead and arsenic, and specific pesticides or herbicides. This page compiles peer-reviewed research studies and scholarly articles that investigate the causes, effects, diagnosis, and management of poisoning in horses.
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
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.
Machado M, Queiroz-Machado CRR, Gardner DR, Castro MB, Câmara ACL, Pimentel LA, Galiza GJN, Riet-Correa F.Leucaena leucocephala poisoning is reported in horses in different Brazilian regions. The poisoning occurred one month after the horses were introduced into paddocks invaded by the plant or after 10 days of consuming cut Leucaena administered as the only food. Affected horses showed moderate to severe hair loss on the mane and tail, orthokeratotic hyperkeratosis with marked follicular telogenization, and hyperplasia of thyroid follicular cells. Mimosin concentration in leaves (5.5 mg/g) was determined by a new HLPC-UV method which is also reported.
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...
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....
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.
Decloedt A, Verheyen T, De Clercq D, Sys S, Vercauteren G, Ducatelle R, Delahaut P, van Loon G.Horses are extremely susceptible to ionophore intoxication. Although numerous reports are available regarding monensin, little is known about lasalocid toxicity. Objective: To describe accidental lasalocid poisoning on a farm in Belgium. Methods: Eighty-one horses, of which 14 demonstrated clinical signs from day 0-21 after being fed a new concentrate batch. One horse died on day 20 and another on day 27. Methods: The most severe cases (n = 7), admitted to the clinic on day 29-46, underwent cardiac examination and blood biochemical analysis, including determination of plasma cardiac troponin...
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 ...
Dickinson CE, Traub-Dargatz JL, Dargatz DA, Bennett DG, Knight AP.To determine the clinical manifestations, morbidity, mortality, and treatment methods for rattlesnake venom poisoning in horses. Methods: Retrospective analysis of medical records. Methods: 27 horses with acute venom poisoning attributable to prairie rattlesnakes, and 5 with chronic problems subsequent to a rattlesnake bite. Results: Most horses were bitten on or near the muzzle while on pasture, resulting in head swelling, dyspnea, and epistaxis. Additional manifestations of acute poisoning included fever, tachycardia, tachypnea, cardiac arrhythmia, hemolytic anemia, thrombocytopenia, hemorrh...
Edwards WC, Edwards RM, Ogden L, Whaley M.Cantharidin content of male and female Epicauta occidentalis and E conferta was determined. Aspects of the life cycle of blister beetles, taxonomy, pheromonal and adaptive functions of cantharidin relative to the medico-legal aspects of cantharidin poisoning, prevention and control in horses are discussed.
van Weeren PR, Morales JA, Rodríguez LL, Cedeño H, Villalobos J, Poveda LJ.This article describes a case of massive mortality among horses which was probably due to intoxication by pyrrolizidine alkaloids from Heliotropium indicum. Over 4 years more than 75% of a population of about 110 horses on a farm in Costa Rica died after showing nervous neurological symptoms. Two clinical manifestations were encountered, an acute and a chronic one, both with a fatal outcome. Pathological findings in 2 horses coincided with those reported in the literature for intoxication by pyrrolizidine alkaloids and were not specific for VEE. However Venezuelan equine encephalitis (VEE) was...
Landolt G, Feige K, Schöberl M.The present study describes the poisoning due to Robinia pseudoacacia in two horses. One of the horses showed mainly intestinal symptoms such as decreased intestinal motility and obstipation of the pelvic flexure. In the second animal central nervous symptoms were predominant. It showed intermittent phases of somnolence alternating with phases of excitation and head pressing. In addition mydriasis and a lacking menace response could be observed. Sensation to the head and the spinal reflexes were reduced. Symptomatic treatment was initiated in both animals and recovery occurred within 2 days.
Rollinson J, Taylor FG, Chesney J.Six cases of accidental salinomycin poisoning in horses are described. The horses were fed a contaminated ration and presented clinical signs which were extremely varied in nature and severity. However, the range of signs, including anorexia, colic, weakness and ataxia bore similarities to those described in horses poisoned with the related ionophore monensin. Other similarities became apparent in serum biochemical profiles of the clinical cases. Although ionophore toxicity is rarely reported in horses they appear to be particularly susceptible, and it should therefore be considered as a diffe...
Gy C, Leclere M, Bélanger MC, Allano M, Beauchamp G, Lavoie JP.Monensin is highly toxic to horses and inadvertent ingestion can result in cardiac injury and death. Objective: To describe sequelae of monensin ingestion and to determine clinical predictors of outcome. Methods: Observational clinical study. Methods: Physical examination, electrocardiogram and echocardiography were performed on 76 horses accidentally exposed to monensin-contaminated feed. Four horses were examined within 14 days of exposure (acute period), 29 horses were examined between 15 and 45 days post-exposure (subacute period) and 70 horses were examined 4-10 months after exposure ...
Gu XL, Dai FY, Xiao X, Li GZ, Zhang LM, Qu WJ.The effect of Ageratina adenophora on pathological characteristics of the liver and lungs as well as serum biochemical parameters in horses were investigated. Ten horses without ingestion history of Ageratina adenophora were classified into the control group, and 10 poisoned but survived horses with 3 months ingestion history were set as the case group. Results showed that serum AST, ALT, ALP, magnesium and phosphorus were elevated significantly, while creatinine was decreased remarkably. Hematoxylin and eosin staining of liver tissues showed diffuse swelling or destruction of hepatocytes, nar...
Hooper PT.Severe spongy degeneration of the central nervous system (CNS) was seen in 11 cattle, 19 sheep, 4 pigs and 1 goat, associated with a variety of hepatic diseases, particularly those caused by hepatotoxic pyrrolizidine alkaloids. It was also seen in a milder form in 2 of 8 horses examined, 1 dog of 5 dogs examined, and in 1 rabbit only of a large number of laboratory animals examined. This paper reports results of experiments which confirmed initially that the CNS disease cold be caused by pyrrolizidine alkaloid intoxication. This was done by poisoning lambs with lasiocarpine. As the disease was...
Smith S, Naylor RJ, Knowles EJ, Mair TS, Cahalan SD, Fews D, Dunkel B.Acorn toxicity has been anecdotally reported to cause fatal colitis and colic in horses but reports in the scientific literature are sparse. Objective: This study reports the diagnosis, treatment, prognosis and outcome of 9 cases with suspected acorn toxicity admitted to 2 referral hospitals. Methods: Retrospective case series. Methods: Case records from 2004 to 2013 were reviewed. Horses were included in the study if they met 3 of 4 criteria: exposure to acorns; clinical and laboratory data suggesting alimentary or renal dysfunction; acorn husks in the faeces or gastrointestinal tract; and ne...
Easterwood L, Chaffin MK, Marsh PS, Porter B, Barr C.66 horses were potentially exposed to phosphine (a gas) 14 hours after being fed a pelleted ration treated with aluminum phosphide. Results: 28 horses had clinical signs of profuse sweating, tachycardia, tachypnea, pyrexia, ataxia, seizures, and widespread muscle tremors. Clinically relevant laboratory findings included hypoglycemia and high plasma concentrations of lactate and ammonia and activities of gamma-glutamyl transpeptidase, aspartate aminotransferase, and alkaline phosphatase. At least 4 horses had signs consistent with hepatic encephalopathy. Necropsy findings included petechial and...
Newton TA, Rose SR.Phenylbutazone is a potent nonsteroidal, anti-inflammatory drug often used by veterinarians to treat racetrack animals. Its use in human beings is limited because of significant adverse effects and the availability of newer, safer drugs. We report the case of a 24-year-old man who ingested 17 g of equine phenylbutazone over a 24-hour period to treat the pain of a toothache. He developed grand mal seizures, coma, hypotension, respiratory and renal failure, and hepatic injury. Serum phenylbutazone concentration obtained approximately eight hours after presentation was 900 micrograms/mL. The pati...
Qualls HJ, Holbrook TC, Gilliam LL, Njaa BL, Panciera RJ, Pope CN, Payton ME.The efficacy of orally administered therapeutics for the treatment of cantharidin intoxication has not been evaluated in controlled studies. Objective: To develop a model of acute cantharidin intoxication in laboratory rats and to evaluate in this model the relative efficacy of 3 gastrointestinal therapies used to treat equine cantharidin toxicosis. Methods: Sixty-four male Sprague-Dawley rats. Methods: A blinded, randomized, controlled study was performed on rats surgically implanted with telemetry transmitters for evaluating heart rate, locomotor activity, and body temperature. Orogastric ad...
Davis EO, Curran GE, Hetherington WT, Norris DA, Wise GA, Roth IJ, SeaWright AA, Bryden WL.Flood plain staggers, a corynetoxicosis of grazing livestock, occurred on flood plains of the Darling river in northern New South Wales between spring 1990 and autumn 1991, associated with the grazing of Agrostis avenacea with diseased inflorescences. Over this period 1722 cattle, 2466 sheep and 11 horses died on 31 farms. Clinical signs were similar in sheep and cattle, being characterised by intermittent episodes of cerebral convulsion superimposed on varying degrees of cerebellar dysfunction. Pathological changes were variable and non-specific, principally reflecting trauma and the generali...
Lacerda MDSC, Wilson TM, Argenta VLS, de Araújo Pinto ÉG, E Macêdo JTSA, Soto-Blanco B, Keller KM, Ocampos Pedroso PM, Câmara ACL.The present report describes the clinical and pathological changes induced by the consumption of oats contaminated with Crotalaria spectabilis seeds by horses. Eighty horses were exposed to oats containing 10 g/kg of C. spectabilis seeds with 0.46% pyrrolizidine alkaloids, and 21 horses died within a 6-month period. Clinical signs included jaundice, apathy, a hypotonic tongue, ataxia, hyporexia, weight loss, aimless wandering, violent behavior, and proprioceptive deficits. Pathological findings were predominant in the liver and included periportal bridging fibrosis, megalocytosis, centrilobul...
Müntener CR, Bruckner L, Kupper J, Althaus F, Caduff-Janosa P.167 adverse reactions of Swissmedic-authorized veterinary medicinal products were reported during the year 2011 (2010: 160). Species and drug classes remain comparable with previous years: most of the reactions occurred following the use of antiparasitic products (39 %), antiinfectives (20 %) or non-steroidal antiinflammatory drugs (11 %) in companion animals (85 dogs and 27 cats) followed by cattle/calves (37). We received 15 cases of adverse reactions following reconverted use, 8 of them in treated cats. Additionally the Swiss Toxicological Information Centre in Zürich processed 84 enquirie...
Lovett A, Vokes J, Loghides N, Johnstone L, Sykes B.Formalin intoxication via the gastrointestinal route has not been previously reported in the horse. Whereas ingestion of formalin in humans, although rare, is well documented. Majority of human cases are either accidental, suicidal or homicidal and often lead to fatality, with a reported lethal formaldehyde dose equating to 0.12 - 0.16 g/kg bwt. Objective: To describe a single case report of the clinical management of an adult horse referred to a veterinary teaching hospital following accidental administration of 10% formalin via nasogastric tube. Methods: A 13-year-old Thoroughbred gelding or...
Mollenhauer HH, Rowe LD, Witzel DA.Heart, diaphragm, and rear limb muscle from ponies and rats treated with monensin were examined by light and electron microscopy. In both species, mitochondrial aberrations were observed in selected muscle cells. The aberrations consisted of loss of matrix substance (vacuolization) usually accompanied by swelling. Vacuolated mitochondria were characterized by an almost total loss of matrix substance with retention of the rudimentary cristae form. In ponies, most vacuolated mitochondria were observed in heart muscle though some also were found in the diaphragm. In rats, most vacuolated mitochon...
Barnard BJ.The most obvious symptoms of rabies in farm animals and pets in South Africa and South-West Africa are discussed in the light of information obtained during routine examination of specimens for the 10-year-period 1967--1976. More than 55% of the cases encountered were cattle in which the most obvious symptoms were salivation (92%), bellowing (69%), aggressiveness (47%), paresis or paralysis (30%) and straining (12%). Unlike cattle, the most obvious symptom in goats was aggressiveness (83%). Salivation was observed in ony 29% of goats but, like bellowing in cattle, bleating was very obvious in ...
Snowden NJ, Helyar CV, Platt SR, Penderis J.Moxidectin is a macrocyclic lactone related to ivermectin used in horses and dogs for endoparasite treatment and prophylaxis. The clinical and neurological presentation of moxidectin toxicity in two dogs following inadvertent poisoning with a moxidectin-containing equine de-worming medication is reported here. In both the dogs, the predominant clinical signs were generalised tremors and ataxia. Moxidectin exerts its neurotoxic effects in mammals by potentiating the effect of gamma-aminobutyric acid and, consistent with this, both the dogs demonstrated a poor response to treatment with diazepam...
Sander J, Cavalleri JM, Terhardt M, Bochnia M, Zeyner A, Zuraw A, Sander S, Peter M, Janzen N.Hypoglycin A (2-amino-3-(2-methylidenecyclopropyl)propanoic acid) is the plant toxin shown to cause atypical myopathy in horses. It is converted in vivo to methylenecyclopropyl acetic acid, which is transformed to a coenzyme A ester that subsequently blocks beta oxidation of fatty acids. Methylenecyclopropyl acetic acid is also conjugated with carnitine and glycine. Acute atypical myopathy may be diagnosed by quantifying the conjugates of methylenecyclopropyl acetic acid plus a selection of acyl conjugates in urine and serum. We describe a new mass spectrometric method for sample volumes of <0...
Bauquier J, Stent A, Gibney J, Jerrett I, White J, Tennent-Brown B, Pearce A, Pitt J.Investigation of toxicosis caused by Malva parviflora was required after 4 horses from the same farm developed severe muscle fasciculations, tachycardia, sweating and periods of recumbency leading to death or euthanasia after ingesting the plant. Objective: To describe historical, clinical, clinicopathological and pathological findings of 4 horses with suspected M. parviflora toxicosis. The role of cyclopropene fatty acids (found in M. parviflora) and mechanism for toxicosis are proposed. Methods: Case series. Methods: Historical, physical examination, clinicopathological and pathological find...
