Grass Sickness is a debilitating and often fatal disease affecting the gastrointestinal tract of horses. It is characterized by damage to the autonomic nervous system, leading to impaired gut motility and digestive function. The condition is classified into acute, subacute, and chronic forms, each varying in severity and progression. The exact cause of Grass Sickness remains unknown, though it is believed to involve a combination of environmental, dietary, and microbial factors. Common clinical signs include colic, difficulty swallowing, and weight loss. This page compiles peer-reviewed research studies and scholarly articles that explore the epidemiology, pathophysiology, and potential risk factors associated with Grass Sickness in horses.
McGorum BC, Davey T, Dosi MCM, Keen JA, Morrison LR, Pirie RS, Shaw DJ, Harris JB.Equine grass sickness (EGS) is a frequently fatal multisystem neuropathy of equids. The aetiology is unknown; proposed causes include toxicoinfection with Clostridium botulinum and a mycotoxicosis. The effect of EGS on the organisation and structural integrity of the skeletal neuromuscular junction (NMJ), the target of botulinum neurotoxins (BoNTs), is unknown. Objective: To compare the organisation and structural integrity of skeletal NMJs from EGS horses, control horses and one horse with a presumptive diagnosis of botulism. Methods: Blinded, retrospective case control. Methods: NMJs in samp...
Quéré E, Volmer C, Mespoulhès-Rivière C.Diagnosing equine grass sickness (EGS) requires histopathological evidence of chromatolysis and/or neuronal loss in peripheral autonomic ganglia. Previous investigators performed postmortem biopsies of gustatory papillae located on the tongue and found chromatolytic subgemmal neurons in all 13 EGS horses. The present study aimed to design a standardized lingual biopsy sampling method through a transbuccal approach in healthy standing horses and assess the quality of the obtained samples, to allow antemortem diagnosis of EGS in clinical cases. Methods: 6 healthy horses. Methods: A transbuccal a...
Stang FL, Bjerregaard R, Müller CE, Ergon Å, Halling M, Thorringer NW, Kidane A, Jensen RB.Carbohydrates in forages constitute an important part of the feed ration for all horses. The aim of the present study was to investigate the effect of harvest time on carbohydrate composition and digestion of various grass species. The experiment was divided into three parts 1) characterization of the chemical composition of experimental feeds (6 grass species: meadow fescue [MF], cocksfoot [CF], perennial ryegrass [PR], smooth bromegrass [SB], tall fescue [TF], and timothy [TI], and 3 harvest times: early, medium, and late first cut), 2) measurements of the in vitro digestion of selected expe...
Weinert-Nelson JR, Meyer WA, Williams CA.Warm-season grasses have been suggested as alternative low non-structural carbohydrate (NSC) pasture forages. The purpose of this study was to evaluate nutrient composition and diurnal changes in soluble carbohydrates for the warm-season annual 'Quick-N-Big' crabgrass [CRB; Digitaria sanguinalis (L.) Scop.] and the warm-season perennial 'Wrangler' bermudagrass [BER; Cynodon dactylon (L.) Pers] in comparison to mixed cool-season grass [CSG; 'Inavale' orchardgrass (Dactylis glomerata [L.]), 'Tower' tall fescue (Lolium arundinaceum [Schreb.] Darbysh.), and 'Argyle' Kentucky bluegrass (Poa prat...
McGorum BC, Chen Z, Glendinning L, Gweon HS, Hunt L, Ivens A, Keen JA, Pirie RS, Taylor J, Wilkinson T, McLachlan G.Equine grass sickness (EGS) is a multiple systems neuropathy of grazing horses of unknown aetiology. An apparently identical disease occurs in cats, dogs, rabbits, hares, sheep, alpacas and llamas. Many of the risk factors for EGS are consistent with it being a pasture mycotoxicosis. To identify potential causal fungi, the gastrointestinal mycobiota of EGS horses were evaluated using targeted amplicon sequencing, and compared with those of two control groups. Samples were collected post mortem from up to 5 sites in the gastrointestinal tracts of EGS horses (EGS group; 150 samples from 54 horse...
Laus F, Corsalini J, Mandara MT, Bazzano M, Bertoletti A, Gialletti R.Equine grass sickness (EGS) has been reported in several European and extra-European countries. Despite this, no scientific paper about clinical cases of EGS in Italy has been published. EGS is a disease affecting almost exclusively horses kept on pasture, characterized by clinical signs related to lesions in autonomic nervous system (ANS), particularly in the enteric nervous system (ENS). According to clinical presentation, acute, subacute and chornic syndromes can be observed, with various sympthoms including dullness, anorexia, dysphagia, drooling of saliva, tachycardia, ptosis, patchy swea...
Kramer KJ, Kagan IA, Lawrence LM, Smith SR.Ethanol-soluble carbohydrates (ESCs) of cool-season grasses include mono- and disaccharides and sometimes short-chain fructans, which may exacerbate the risk of pasture-associated laminitis. A calibration for prediction of ESC concentrations by near-infrared reflectance spectroscopy (NIRS) was developed from 323 samples of four cool-season grass species (orchardgrass, Kentucky bluegrass, tall fescue, and perennial ryegrass) across 10 cultivars collected in central Kentucky in the morning and afternoon over two growing seasons. The calibration, which had accuracy above 95%, was used to predict ...
Vincze B, Varga M, Kutasi O, Zenke P, Szenci O, Baska F, Bartels A, Spisák S, Cseh S, Solymosi N.Equine grass sickness (also known as dysautonomia) is a life-threatening polyneuropathic disease affecting horses with approx. 80% mortality. Since its first description over a century ago, several factors, such as the phenotype, intestinal microbiome, environment, management and climate, have been supposed to be associated with the increased risk of dysautonomia. In this retrospective study, we examined the possible involvement of genetic factors. Medical and pedigree datasets regarding 1,233 horses with 49 affected animals born during a 23-year period were used in the analysis. Among the des...
Piccinelli C, Jago R, Milne E.Equine dysautonomia (grass sickness) is characterized by autonomic neuronal degeneration and is often fatal. As outbreaks occur, rapid diagnosis is essential but confirmation currently requires histological examination. This study evaluated diagnostic accuracy of cytological examination of cranial cervical ganglion (CCG) scrapings for dysautonomia diagnosis. CCG smears from 20 controls and 16 dysautonomia cases were stained with May-Grünwald Giemsa (MGG), hematoxylin and eosin (HE), and cresyl fast violet (CFV), with HE-stained histological sections of CCG as gold standard for diagnosis. Exam...
Kenny LB, Ward D, Robson MG, Williams CA.Many methods exist for estimating species composition, but few studies compare those useful in improved horse pastures. The objective of this study was to examine 4 techniques for estimating desirable forage species composition in 2 cool-season horse pastures based on prevalence estimates, repeatability, bias, and practicality, and to select a method for use in a subsequent grazing study. The techniques included Equine Pasture Evaluation Disc (EPED), Line-Point Intercept with 3 transects of 50 observations each (LPI 3-50), LPI with 5 transects of 30 observations each (LPI 5-30), and Step Point...
Carranza J, Yoong WA, Vergara BC, Briones A, Mateos C.Reproductive phenology is an important trait subjected to natural selection. Current horses in America belong to the Palearctic original populations after being introduced by European colonizers. Photoperiod variation is the main environmental factor for the adjustment of reproductive timing in horses, but is absent in equatorial areas. Here we hypothesize that seasonality of green-grass availability may influence breeding phenology in equatorial regions. We used data of 929 services to mares from 2006 to 2011 in a thoroughbred equine exploitation in Ecuador that experienced strong grass seaso...
Leng J, Proudman C, Darby A, Blow F, Townsend N, Miller A, Swann J.Equine grass sickness (EGS) is a frequently fatal disease of horses, responsible for the death of 1 to 2% of the U.K. horse population annually. The etiology of this disease is currently uncharacterized, although there is evidence it is associated with Clostridium botulinum neurotoxin in the gut. Prevention is currently not possible, and ileal biopsy diagnosis is invasive. The aim of this study was to characterize the fecal microbiota and biofluid metabolic profiles of EGS horses, to further understand the mechanisms underlying this disease, and to identify metabolic biomarkers to aid in diagn...
Randleff-Rasmussen PK, Leblond A, Cappelle J, Bontemps J, Belluco S, Popoff MR, Marcillaud-Pitel C, Tapprest J, Tritz P, Desjardins I.Equine grass sickness (EGS) (equine dysautonomia) is a neurodegenerative condition of grazing equines. Pre-mortem diagnosis of EGS is a challenge for practitioners as definitive diagnosis requires ileal/myenteric lymph node biopsies. This study aimed to develop a clinical score that could be used by practitioners to improve the detection of acute or subacute EGS cases in the field. Suspected EGS cases were declared by veterinary practitioners. A case was classified as confirmed positive if ileal or rectal biopsy samples showed neuronal degeneration typical of EGS. A semi-quantitative scoring s...
Jago RC, Scholes S, Mair TS, Pearson GR, Pirie RS, Handel I, Milne EM, Coyle F, Mcgorum BC.An accurate, minimally invasive, ante-mortem diagnostic test for equine grass sickness (EGS) is currently lacking. Although histological examination of haematoxylin and eosin-stained rectal biopsies for chromatolytic neurons is insensitive as a diagnostic test for EGS, we hypothesised that its diagnostic accuracy could be improved by immunolabelling for β-amyloid precursor protein (β-APP), which has increased expression in cranial cervical ganglia (CCG) neuronal perikarya in EGS. Objective: To develop a grading scheme for assessing the distribution and intensity of β-APP immunoreactivity wi...
McGorum BC, Jago RC, Cillan-Garcia E, Pirie RS, Keen JA, Reardon RJM, Saffu PY, Miller NJ.The aetiology of equine grass sickness (EGS) is currently unknown. We hypothesised that an acute deficiency of niacin (vitamin B3), which plays a key role in neural homeostasis, may contribute to neurodegeneration in EGS. Niacin deficiency can potentially result from ingestion of niacin antagonists produced by pasture mycotoxigenic fungi. Objective: To compare the niacin status of EGS and control grazing horses. A secondary objective was to compare blood concentrations of vitamins B1, B2 and B6 in EGS and control grazing horses to determine if the status of these vitamins was altered in EGS. M...
Ireland JL, McGorum BC, Proudman CJ, Newton JR.Without an experimental model of equine grass sickness (EGS), a randomised controlled field trial (RCT) represents the only method of evaluating the efficacy of Clostridium botulinum type C vaccination in preventing naturally occurring disease. Clinical trial feasibility is an important aspect of preliminary work undertaken prior to initiating RCTs, estimating parameters that are important for study design. This cross-sectional study aimed to assess the feasibility of conducting a nationwide RCT of a candidate vaccine for EGS based on responses from a sample of British equine veterinary practi...
Jago RC, Handel I, Hahn CN, Pirie RS, Keen JA, Waggett BE, McGorum BC.Objective criteria for predicting survival of chronic grass sickness cases are currently lacking. Objective: To determine whether the rate and/or magnitude of bodyweight change during hospitalisation of chronic grass sickness cases can provide an objective predictor of survival to discharge from hospital. Clinicians' recorded indication(s) for euthanasia were also reviewed. Methods: Single centre retrospective observational study. Methods: Case records of all horses admitted for management of chronic grass sickness to The Dick Vet Equine Hospital between 1998 and 2013 were analysed. Case backg...
McGorum BC, Scholes S, Milne EM, Eaton SL, Wishart TM, Poxton IR, Moss S, Wernery U, Davey T, Harris JB, Pirie RS.Equine grass sickness (EGS) is of unknown aetiology. Despite some evidence suggesting that it represents a toxico-infection with Clostridium botulinum types C and/or D, the effect of EGS on the functional targets of botulinum neurotoxins, namely the soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins, is unknown. Further, while it is commonly stated that, unlike EGS, equine botulism is not associated with autonomic and enteric neurodegeneration, this has not been definitively assessed. Objective: To determine: 1) whether botulism causes autonomic and enteric neurodeg...
McGorum BC, Pirie RS, Shaw D, Macintyre N, Cox A.Diagnosis of equine grass sickness (EGS) can be challenging. We hypothesised that subgemmal plexus neurons are chromatolytic in EGS. If correct, histopathological examination of gustatory papillae biopsies could aid premortem diagnosis of EGS, and EGS could represent a spontaneous model of subgemmal neuronal chromatolysis to facilitate study of the pathology of structures involved in taste. Objective: To compare subgemmal plexi and gustatory papillae in EGS and control horses. Methods: Observational study. Methods: Conventional histology and immunohistochemistry were used to compare subgemmal ...
Wylie CE, Shaw DJ, Fordyce FM, Lilly A, Pirie RS, McGorum BC.We hypothesised that the apparent geographical distribution of equine grass sickness (EGS) is partly attributable to suboptimal levels of soil macro- and trace elements in fields where EGS occurs. If proven, altering levels of particular elements could be used to reduce the risk of EGS. Objective: To determine whether the geographical distribution of EGS cases in eastern Scotland is associated with the presence or absence of particular environmental chemical elements. Methods: Retrospective time-matched case-control study. Methods: This study used data for 455 geo-referenced EGS cases and 910 ...
McGorum BC, Pirie RS, Eaton SL, Keen JA, Cumyn EM, Arnott DM, Chen W, Lamont DJ, Graham LC, Llavero Hurtado M, Pemberton A, Wishart TM.Equine grass sickness (EGS) is an acute, predominantly fatal, multiple system neuropathy of grazing horses with reported incidence rates of ∼2%. An apparently identical disease occurs in multiple species, including but not limited to cats, dogs, and rabbits. Although the precise etiology remains unclear, ultrastructural findings have suggested that the primary lesion lies in the glycoprotein biosynthetic pathway of specific neuronal populations. The goal of this study was therefore to identify the molecular processes underpinning neurodegeneration in EGS. Here, we use a bottom-up approach be...
Malekinejad H, Alizadeh-Tabrizi N, Ostadi A, Fink-Gremmels J.The pathogenesis of equine grass sickness (EGS) has not fully understood. A better understanding of the exact pathogenesis of diseases can help to make an accurate diagnosis. Previous studies reported some pathological damage of neuronal cells in EGS patients. In this study, primarily cytotoxicity of serum from three clinically EGS-diagnosed horses on PC12 Tet-off (PTO) cells was assessed. Subsequently, the apoptotic tests including cytochrome C release, caspase-3/7 activity measurement and DNA fragmentation assay were conducted to clarify the apoptotic effect of serum from EGS patients. Addit...
McGorum BC, Pirie RS, Glendinning L, McLachlan G, Metcalf JS, Banack SA, Cox PA, Codd GA.While toxins from aquatic cyanobacteria are a well-recognised cause of disease in birds and animals, exposure of grazing livestock to terrestrial cyanobacteria has not been described. This study identified terrestrial cyanobacteria, predominantly Phormidium spp., in the biofilm of plants from most livestock fields investigated. Lower numbers of other cyanobacteria, microalgae and fungi were present on many plants. Cyanobacterial 16S rDNA, predominantly from Phormidium spp., was detected in all samples tested, including 6 plant washings, 1 soil sample and ileal contents from 2 grazing horses. F...
Pirie RS, Jago RC, Hudson NP.Equine grass sickness (EGS; equine dysautonomia) is a polyneuronopathy affecting both the central and the peripheral nervous systems of horses. As the name implies, EGS almost exclusively affects grazing horses, resulting in the development of a characteristic array of clinical signs, most of which can be attributed to neuronal degeneration in the autonomic and enteric nervous systems. Varying disease severities occur, largely determined by the extent of neuronal degeneration in the myenteric and submucous plexuses of the enteric nervous system. Extensive neuronal degeneration, as seen in acut...
Wylie CE, Shaw DJ, Fordyce FM, Lilly A, McGorum BC.Equine grass sickness (EGS) remains a frequently fatal disease of equids in Britain. Since previous investigations of signalment- and meteorology-related risk factors for EGS have yielded some conflicting data, further investigation is warranted. Objective: To identify signalment- and meteorology-related risk factors for EGS in Scotland. Methods: Retrospective time-matched case-control study. Methods: This study was undertaken using data for 455 EGS cases and 910 time-matched controls that were referred to the Royal (Dick) School of Veterinary Studies, and average UK Meteorological Office weat...
Goren G, Fritz J, Dillitzer N, Hipp B, Kienzle E.Hay stabilises urine pH in horses. It is unknown whether this is an effect of structure or of chemical composition. In this study, four ponies (230-384 kg body weight [BW]) were fed six different diets with either a structure or a composition similar to hay with and without acidifiers in a cross-over experimental design in amounts to maintain body weight with the following main compounds: Fresh grass (GRASS), alfalfa hay (ALF), grass cobs (COBS), grass silage (SIL), straw (STR) or extruded straw (STRe) for 2 to 10 days. Urine pH was measured in all trials, blood pH, blood base excess and bicar...
Garrett LA, Brown R, Poxton IR.This study compares quantitatively the microbiota of the gastrointestinal tract of healthy horses with that of horses with equine grass sickness (EGS). Faecal and ileal samples were cultured quantitatively on selective and non-selective media. Confirmed anaerobes were identified to species level. Overall faecal counts gave a ratio of aerobes:anaerobes of approximately 1:1. However, the mean counts in healthy horses of 4.4x10(8) aerobes:3.7x10(8) anaerobes per gram wet weight were different from counts in EGS (means were 10-100-fold higher), with statistically significant differences for the an...
McGorum BC, Pirie RS, Glendinning L, McLachlan G, Metcalf JS, Banack SA, Cox PA, Codd GA.While toxins from aquatic cyanobacteria are a well-recognised cause of disease in birds and animals, exposure of grazing livestock to terrestrial cyanobacteria has not been described. This study identified terrestrial cyanobacteria, predominantly Phormidium spp., in the biofilm of plants from most livestock fields investigated. Lower numbers of other cyanobacteria, microalgae and fungi were present on many plants. Cyanobacterial 16S rDNA, predominantly from Phormidium spp., was detected in all samples tested, including 6 plant washings, 1 soil sample and ileal contents from 2 grazing horses. F...
Hunter LC, Miller JK, Poxton IR.The cause of grass sickness, an equine dysautonomia, is unknown. The disease usually results in death. Gastrointestinal (GI) dysfunction is a common clinical manifestation in all forms of the disease. It is generally thought that equine grass sickness (EGS) is caused by an ingested or enterically produced neurotoxin which is absorbed through the GI tract. Clostridium botulinum was first implicated as a causative agent when it was isolated from the GI tract of a horse with EGS in 1919. The aim of the present study was to investigate the hypothesis that EGS results from toxicoinfection with C. b...
French NP, McCarthy HE, Diggle PJ, Proudman CJ.Equine grass sickness (EGS) is a largely fatal, pasture-associated dysautonomia. Although the aetiology of this disease is unknown, there is increasing evidence that Clostridium botulinum type C plays an important role in this condition. The disease is widespread in the United Kingdom, with the highest incidence believed to occur in Scotland. EGS also shows strong seasonal variation (most cases are reported between April and July). Data from histologically confirmed cases of EGS from England and Wales in 1999 and 2000 were collected from UK veterinary diagnostic centres. The data did not repre...
Leng J, Proudman C, Darby A, Blow F, Townsend N, Miller A, Swann J.Equine grass sickness (EGS) is a frequently fatal disease of horses, responsible for the death of 1 to 2% of the U.K. horse population annually. The etiology of this disease is currently uncharacterized, although there is evidence it is associated with Clostridium botulinum neurotoxin in the gut. Prevention is currently not possible, and ileal biopsy diagnosis is invasive. The aim of this study was to characterize the fecal microbiota and biofluid metabolic profiles of EGS horses, to further understand the mechanisms underlying this disease, and to identify metabolic biomarkers to aid in diagn...
Pirie RS, Jago RC, Hudson NP.Equine grass sickness (EGS; equine dysautonomia) is a polyneuronopathy affecting both the central and the peripheral nervous systems of horses. As the name implies, EGS almost exclusively affects grazing horses, resulting in the development of a characteristic array of clinical signs, most of which can be attributed to neuronal degeneration in the autonomic and enteric nervous systems. Varying disease severities occur, largely determined by the extent of neuronal degeneration in the myenteric and submucous plexuses of the enteric nervous system. Extensive neuronal degeneration, as seen in acut...
Copas VE, Durham AE, Stratford CH, McGorum BC, Waggett B, Pirie RS.Equine grass sickness (EGS) is a debilitating and often fatal neurodegenerative disease. A presumptive diagnosis of EGS may be made on the basis of clinical signs and subjective ancillary tests, but a definitive antemortem diagnosis can only be made following histopathological examination of intestinal biopsies. It has previously been reported that horses with EGS may show clinical and clinicopathological signs of systemic inflammation. The objective of this study was to (a) quantify acute inflammatory markers in blood samples collected from acute, subacute and chronic EGS cases, and (b) compa...
McGorum BC, Pirie RS, Eaton SL, Keen JA, Cumyn EM, Arnott DM, Chen W, Lamont DJ, Graham LC, Llavero Hurtado M, Pemberton A, Wishart TM.Equine grass sickness (EGS) is an acute, predominantly fatal, multiple system neuropathy of grazing horses with reported incidence rates of ∼2%. An apparently identical disease occurs in multiple species, including but not limited to cats, dogs, and rabbits. Although the precise etiology remains unclear, ultrastructural findings have suggested that the primary lesion lies in the glycoprotein biosynthetic pathway of specific neuronal populations. The goal of this study was therefore to identify the molecular processes underpinning neurodegeneration in EGS. Here, we use a bottom-up approach be...
Pogson DM, Doxey DL, Gilmour JS, Milne EM, Chisholm HK.Histological investigations were undertaken on four sympathetic autonomic ganglia and on the myenteric and sub-mucosal plexuses of the jejunum in healthy animals, in naturally occurring cases of acute, sub-acute and chronic equine dysautonomia and in ponies in which neuronal damage had been induced by the injection of acute grass sickness sera. The degree of neuronal damage is related to the type of dysautonomia. The coeliac-mesenteric ganglion reacts differently from other ganglia and is less severely damaged in cases of short duration. Extensive experimentally induced damage to the coeliac-m...
Scholes SF, Vaillant C, Peacock P, Edwards GB, Kelly DF.The degeneration of enteric neurones has been recorded in grass sickness, but the distribution of the lesions in the gut and their possible relationship with the severity of the clinical signs has not been established. Samples obtained from 11 anatomically defined sites along the gastrointestinal tract of eight control horses without gastrointestinal disease, five horses with acute grass sickness and three horses with chronic grass sickness were examined histologically. The organisation of the enteric ganglia was similar to that in other large mammalian species. Minor exceptions included the p...
Cottrell DF, McGorum BC, Pearson GT.Autonomic dysfunction constitutes a prominent clinical feature of equine grass sickness (EGS). Significant injury to the nervous control of the alimentary system is life threatening, partly because of dysphagia but also because of the failure of the unique regulatory mechanisms in equine digestion involving water and electrolyte balance. The neuropathology also indicates the presence of a somatic polyneuropathy. The morphological features of EGS are similar to those of excitotoxic neuronal degeneration, which resembles neuronal apoptosis. It is difficult to ascertain from published accounts th...
Uzal FA, Robles CA, Olaechea FV.'Mal seco' is a grass sickness-like syndrome of horses in Argentina. A histopathological study was made of the coeliaco-mesenteric ganglia of four horses with 'mal seco' and of four horses that died from other causes. The severity and extent of the lesions found in the horses with 'mal seco' was greatest in the two with the shortest clinical course. Degenerative changes consisted mainly in the loss of Nissl substance, cytoplasmic vacuoles, neuronophagia, intercellular and intracytoplasmic eosinophilic bodies, and pyknotic and eccentric nuclei. The coeliaco-mesenteric ganglia of the control hor...
Bailey SR, Marr CM, Elliott J.Acute laminitis has been associated with the release of compounds, as yet unidentified, produced by hindgut fermentation which affect blood flow to the digit. The objectives of this study were to identify amine compounds in equine caecal and colonic contents, some of which are known to have vasoactive properties. In addition, the concentrations of amines in caecal contents of horses fed either grass or hay diets were compared. Fifteen amines were identified in equine hindgut contents in concentrations greater than 1 microM. The caecal concentrations of phenylethylamine, isoamylamine, cadaverin...
Hudson N, Mayhew I, Pearson G.Equine dysautonomia (grass sickness) is a frequently fatal disease of horses characterised by intestinal stasis. Interstitial cells of Cajal (ICC) are the pacemakers and mediators of neurotransmission in the gastrointestinal tract. Impaired ICC-mediated control of motility has been implicated in intestinal disorders in laboratory mammals, humans and in equine grass sickness. The aim of this study was to compare the in vitro electrical properties of ileum from grass sickness cases with horses free from gastrointestinal disease. Intracellular microelectrode recordings were made from smooth muscl...
Newton JR, Hedderson EJ, Adams VJ, McGorum BC, Proudman CJ, Wood JL.The reasons why equine grass sickness (EGS) recurs on premises are unknown and, consequently, practical methods for reducing the risk of recurrence are not available. Objective: To identify risk factors associated with recurrence of EGS on premises and to gain possible insights into the pathogenesis of the disease. Methods: Data on disease history and risk factors were collected by postal questionnaire from premises with EGS cases between 1st January 1997 and 31st December 2001. Data on variation in rates of recurrence of EGS for different risk factors were analysed using Poisson regression an...
Hahn CN, Mayhew IG, de Lahunta A.Equine grass sickness (EGS) is an acquired disease of unknown aetiology affecting horses kept at grass. The disease is characterised by postganglionic sympathetic and parasympathetic neuronal pathology and is categorised as a dysautonomia. This study undertook a systematic examination of brain stem cranial nerve nuclei in 59 cases of EGS. Pathology consisting of neuronal chromatolysis was most consistently noted in the lower motor neurons of the general visceral efferent nucleus of CN III and X and the general somatic efferent nuclei of CN III, V, VII and XII. The prevalence of chromatolysis d...
Baker JR, Ellis CE.The causes of death recorded in 480 consecutive post mortem examinations of horses performed at the department of pathology, Veterinary Field Station, University of Liverpool, between February 1958 and February 1980, are reported. The alimentary, locomotor and nervous systems were those most frequently diseased. The most common specific entities were those associated with grass sickness, fractures and endoparasitism.
McCarthy HE, French NP, Edwards GB, Miller K, Proudman CJ.Equine grass sickness (EGS) occurs repeatedly on certain premises over time. Few studies have sought, or identified, the determinants of this phenomenon in order to inform advice on disease prevention strategies. Objective: Premises-level risk factors are important determinants of whether EGS occurs. Methods: A matched case-control study was undertaken. Sixty premises giving rise to one or more histologically confirmed case of EGS and 120 time-matched control premises were sampled. Data were collected on pasture management, soil nutrient content, pasture nutrient content and local weather cond...
Böhnel H, Wernery U, Gessler F.Botulism is caused by different types of Clostridium botulinum, a soil bacterium. Equine grass sickness (equine dysautonomia) is suspected of being a clinical form of this disease. On a stud where this disease occurred twice within 8 months, grass and soil samples and necropsy specimens of one horse were tested for the presence of bacterial forms and toxin of C. botulinum. Different types and type mixtures (A-E) of C. botulinum and botulinum neurotoxin were found. For the first time, it has been shown that green grass blades contain botulinum toxin. The results support the hypothesis that equi...
Wood JL, Milne EM, Doxey DL.A case-control study was performed to investigate the epidemiology of grass sickness in the United Kingdom from 1992 to 1995. Data were collected by means of postal questionnaire when cases of grass sickness were identified. Sets of three questionnaires were posted to owners of, or veterinary surgeons attending, cases of grass sickness, with a request to provide information on the case, on one healthy animal on the same premises as the case and on another healthy animal on other premises. Controls were matched to cases by date of onset. After univariate analyses, the probability of grass sickn...
Wylie CE, Proudman CJ.Equine grass sickness (EGS) is recognized as a debilitating and predominantly fatal neurodegenerative disease affecting grazing equids. The gastrointestinal tract is the most severely affected body system, resulting in the main clinical signs of colic (acute grass sickness), weight loss, or dysphagia (chronic grass sickness). EGS predominantly occurs within Great Britain, although it is also recognized in regions of mainland Europe, and mainly affects young horses with access to pasture in the springtime. There is strong evidence of an association between EGS and the type C toxins produced by ...
Whitwell KE.An autopsy study of one dead and two sick hares from an East Anglian estate on which two mares had died of grass sickness revealed that two of the hares were suffering from a polyganglionopathy and alimentary tract changes, remarkably similar to those seen in grass sickness in horses. No such abnormalities were found in two healthy hares from the same locality.
Doxey DL, Pogson DM, Milne EM, Gilmour JS, Chisholm HK.Damage to the neurons of selected autonomic ganglia was quantified in relation to the severity of the clinical signs shown in acute, subacute and chronic cases of dysautonomia (grass sickness). No connection between the clinical severity of acute or subacute dysautonomia and the amount of neuronal damage in the superior cervical, stellate and coeliaco-mesenteric ganglia could be demonstrated. However, a higher proportion of normal neurons were found in chronic cases. Jejunal submucosal neuronal damage was correlated with clinical severity but further work is required to confirm this finding an...
Kenny LB, Ward D, Robson MG, Williams CA.Many methods exist for estimating species composition, but few studies compare those useful in improved horse pastures. The objective of this study was to examine 4 techniques for estimating desirable forage species composition in 2 cool-season horse pastures based on prevalence estimates, repeatability, bias, and practicality, and to select a method for use in a subsequent grazing study. The techniques included Equine Pasture Evaluation Disc (EPED), Line-Point Intercept with 3 transects of 50 observations each (LPI 3-50), LPI with 5 transects of 30 observations each (LPI 5-30), and Step Point...
McCarthy HE, Proudman CJ, French NP.The geographical spread of grass sickness between 1909 and 1999, particularly in England and Wales, is described, and the experimental investigations to identify a causal agent are summarised. The epidemiological techniques used to investigate grass sickness vary from clinical observations, to more advanced methods such as case-control studies using logistic regression analyses. Several risk factors for grass sickness have been reported consistently (age, time of year and recent movement to new pasture or premises) and several others have been reported for which the findings remain inconsisten...
Waggett BE, McGorum BC, Wernery U, Shaw DJ, Pirie RS.While previous studies have demonstrated an association between equine grass sickness (EGS) and the presence of Clostridium botulinum within ileal contents and faeces, no such associations with other intestinal-derived anaerobic bacteria have been extensively investigated. Objective: The prevalence of C. perfringens in the ileal contents and faeces of EGS horses is greater than control horses; the detection of C. perfringens in faeces by ELISA could be diagnostically beneficial in a clinical setting. Methods: The prevalence of C. perfringens in faeces from EGS horses and healthy grazing contro...
