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.
O'Sullivan BM, Goodwin JA.On 6 properties in south-western Queensland an outbreak of nervous disease occurred horses due to ingestion of Swainsonia (Darling pea). Loss of condition, depression, hyperaesthesia and hyperexcitability were seen in affected horses. At autopsy of 2 horses generalised c ytoplasmic vacuolation was seen in the neurones of the central nervous system and in the liver, adrenal and thyroid. The clinical and pathological features were similar to those described in horses suffering from Swainsona poisoning in Australia and Astragalus and Oxytropis in North America.
Knight HD, Costner GC.During the summer and fall of 1973, a few horses, goats, and cattle in the Napa Valley of California became intoxicated by bromide via the ingestion of volunteer oat hay that had been cut from a field treated with methyl bromide, a soil fumigant. The bromide content of the hay ranged from 6,00 to 8,400 ppm. Signs of intoxication were lethargy, weakness, and ataxia. Animals experimentally fed the contaminated hay developed signs of intoxication between the 7th and 9th days.
Wilson JW.Creatine phosphokinase activity was determined in cerebrospinal fluid samples submitted for analysis from 126 animals suspected of having central nervous system disease. Values less than 1 sigma unit/ml were obtained on 32 samples and values less than or equal to 1 sigma unit/ml were obtained on 94 samples. The creatine phosphokinase values were increased in all cases of feline toxoplasmosis and feline infectious peritonitis. From other cases, especially seizure disorders and suspected poisonings, and apparent aid in prognosis for future cases was identified.
Oehme FW.Animals are constantly exposed to a wide variety of foreign chemicals, many of which are potentially toxic and some of which result in the clinical poisonings. Pesticides are applied on or around animals for the control of insects and rodents. These chemicals may be placed in areas without regard for accessibility to household pets and domestic livestock. Insecticides, herbicides, and fungicides are routinely and haphazardly applied to animal and environmental surfaces alike with apparent disregard for differences in absorptive capability. Fortunately, newer herbicides and fungicides are relat...
Matsuoka T.Gelded horses of mixed breeding, ranging in weight between 360 and 455 kg, were fed pellets that contained monensin at concentrations of 279, 124, 31, and 0 ppm. Of 2 horses fed 279 ppm (253 g/T), both died. Of 3 horses fed 125 ppm (113 g/T), 1 died; feed intake was reduced in the 2 survivors. Of 3 horses fed 31 ppm (28 g/T), 1 had a transitory reduction in feed intake and the other 2 remained clinically normal. The 2 horses fed 0 ppm remained clinically normal. Monensin was also given to horses by gavage, at dosages of 1, 2, 3, 4, or 20 mg/kg of body weight. The LD50 was estimated to be betwe...
Greenway JA, Puls R.Clinical sickness was observed in domestic ducks, geese, horses and swine during October 1973. All species showed upper alimentary distress with mortalities occurring in the geese. Barley derived from a common source had been fed. Examination of the barley revealed invasion by Fusarium spp and detection of a high level of dermatitic fusariotoxins.
Science (New York, N.Y.)May 26, 1975
Volume 188, Issue 4189 738-740 doi: 10.1126/science.1168366
Carter CD, Kimbrough RD, Liddle JA, Cline RE, Zack MM, Barthel WF, Koehler RE, Phillips PE.Tetrachlorodibenzodioxin was identified as the apparent cause of an outbreak of poisoning in humans, horses, and other animals. Exposure was related to the spraying of contaminated waste oil on riding arenas for dust control. The contamination resulted from improper disposal of a toxic industrial waste. The pathologic effects and chemical identification of tetrachlorodibenzodioxin are described.
Harris WF.Three horses exhibited nervous and cardiopulmonary signs after ingestins small amounts of metaldehyde, and 2 died in 3 to 5 hours. A colt given 0.1 mg/kg was similarly affected and died.
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...
Willoughby RA, MacDonald E, McSherry BJ, Brown G.Groups of young growing horses were fed toxic amounts of lead only, zinc only and the same amounts of lead and zinc together. Those fed Pb only developed pharyngeal and laryngeal paralysis ("roaring") whereas those fed Zn only and Pb and Zn together developed the same clinical syndrome which included swelling at the epiphyseal region of the long bones, stiffness and lameness. Anemia and decreased weight gains were most pronounced in animals fed Zn for the longest periods. Animals fed Pb only did not become anemic and weight loss did not occur until after there was an interference in swallowing...
Sander J, Terhardt M, Janzen N.In horses, congenital defects of energy production from long-chain fatty acids have not been described so far. In contrast, inhibition of fatty acid degradation caused by the toxins hypoglycin A and methylenecyclopropylglycine from various maple species are observed frequently. These non-proteinogenic aminoacids are passed on placentally to fetuses or with collostrum or milk to newborn foals. Nevertheless, newborn foals become very rarely symptomatic. Vertical transmission apparently is not sufficient to induce clinical disease without a particular genetic constellation being present. One of t...
Kamphues J, Meyer H, Liebler EM, Johannsen A.Anamnesis and clinical signs of horses form five different stables after ingestion of ionophores are reported and techniques of feed examination are described. Within a few hours or days after feeding of new types or batches of concentrates horses fell ill. They showed colic-like symptoms with intense sweating and ataxia. Most of the sick animals died within a short time span. Samples of the concentrates were analysed and different types and amounts of ionophores were detected. In four cases contamination by monensin in concentrations of less than 5 mg to 679 mg/kg feed were found. One feed sa...
Câmara ACL, de Sousa Argenta VL, de Moraes DDA, Fonseca EF, Fino TCM, Paludo GR, Soto-Blanco B.Determining the prognosis of poisoning by plants containing pyrrolizidine alkaloids is usually challenging. This study aimed to identify important prognostic parameters that can determine the severity of spontaneous poisoning by in horses. Blood samples from 42 horses spontaneously poisoned by oats contaminated with seeds were evaluated. Complete blood counts (CBC) and serum biochemical tests [urea, creatinine, total protein, albumin, total and direct bilirubin concentrations, aspartate aminotransferase (AST), γ-glutamyl transferase (GGT), and creatine kinase (CK) activities] were performed...
Milne EM, Pogson DM, Doxey DL.Poisoning with Senecio jacobaea (ragwort) is a common cause of chronic liver disease in horses in Britain. The major clinical signs are the result of hepatic failure but gastric impaction has recently been associated with the disease. The present paper describes three cases of secondary gastric impaction associated with ragwort poisoning. In each case the impaction was the cause of death or necessitated euthanasia.
Harris WF.Three horses exhibited nervous and cardiopulmonary signs after ingestins small amounts of metaldehyde, and 2 died in 3 to 5 hours. A colt given 0.1 mg/kg was similarly affected and died.
Johnstone LK, Mayhew IG.To investigate the effects of lolitrem B intoxication on renal K(+) secretion in response to increased tubular flow rates. Methods: Results are derived from a repeated measure pilot study of seven horses fed non-perennial ryegrass feed for a week prior to exposing them to perennial ryegrass seed and hay that contained an average of 2 ppm lolitrem B. At the end of the control and treatment period frusemide (1 mg/kg I/V) was administered and serial fractional excretion of K(+)(FEK(+)) and fractional excretion of Na(+)(FENa(+)) calculated. Baseline concentration of aldosterone in plasma, serum K(...
Barr AC, Reagor JC.Horses poisoned by a plant may show a myriad of clinical signs. Awareness of the poisonous plants growing in a given area and those that are likely to appear in hay and their associated clinical signs can be instrumental in making diagnoses. More importantly, the information can be shared with clients to help prevent plant poisonings in horses.
Gish A, Robveille C, Gicquel T, Allorge D, Gault G, Gaulier JM.Analytical detection of Oenanthe crocata toxins in biological samples is challenging because of their instability, the lack of commercially available standards and the exceptionally low detection of these molecules using mass spectrometry. This work aims to report the used analytical methods that allowed identification of the main plant toxins in biological samples from an equid (an Arabian horse) fatality related to hemlock water dropwort (Oenanthe crocata Linnaeus) intake. Using both LC-DAD and LC-HRMS methods allowed identification (i) of oenanthotoxin in roots found on the site, root fragm...
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...
