Science Newsletter Nº5 March 2026

Summary

This edition highlights recent advances across multiple fields of equine medicine, with a strong focus on translating research findings into improved clinical care and performance outcomes. Featured studies explore the link between gastric disease and ridden pain behaviour, cardiovascular consequences of systemic inflammation, and the potential role of intestinal microbiota in atypical myopathy. The newsletter also addresses the clinical presentation and diagnosis of acute leptospirosis, and presents several innovative developments in equine cardiology, including new insights into arrhythmogenic substrates, minimally invasive access to the left heart, and long-term rhythm monitoring using implantable loop recorders. In addition, novel ultrastructural findings in equine grass sickness and evidence supporting heat acclimatisation strategies for elite sport horses further expand our understanding of welfare, pathophysiology, and performance optimisation.

In this edition’s "Do you know…" we get to know Michael Hewetson.
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GASTRIC DISEASE

This novel prospective observational cohort study by Pineau et al., aimed to combine the topical subjects of ridden pain ethograms and gastric disease in sport horses. Nine Warmblood showjumping horses with existing gastric disease underwent standard exercise testing with ridden pain ethogram scoring before a dietary change from a high starch to low starch diet was implemented and maintained for a 12-week period. Repeat gastroscopy, exercise testing and ridden pain scoring was performed after the 12-week period. An improvement was seen in the severity of both gastric lesions and ridden pain scoring. These findings highlight a correlation between gastric pathology and pain-related behaviour, supporting dietary modification as a strategy to improve gastric health and ridden comfort in equine athletes.

SYSTEMIC DISORDERS

An experimental study was performed in donkeys to evaluate the haemodynamic response to lipopolysaccharide infusion, as well as the effect of meloxicam in these animals. The study aimed to investigate the cardiovascular consequences of experimentally induced endotoxaemia in donkeys. Acute endotoxaemia was induced in healthy adult jennies through intravenous administration of lipopolysaccharides, and cardiovascular parameters were closely monitored over time. The infusion resulted in marked haemodynamic alterations, including hypotension, reduced central venous pressure, impaired cardiac function, and increased cardiac troponin I concentrations, indicating myocardial involvement. Echocardiographic evaluation revealed decreased stroke volume and cardiac output, along with signs of ventricular dysfunction. Importantly, intravenous treatment with meloxicam prevented most of these alterations, stabilising haemodynamic variables and cardiac performance. These findings suggest that meloxicam may be an effective therapeutic option to mitigate cardiovascular and haemodynamic disturbances associated with SIRS in donkeys.

This multi-centre study, performed across three equine hospitals in Belgium, investigated whether variations in intestinal microbiota might be present between clinical atypical myopathy cases, co-grazers and unaffected horses, since certain bacterial mitochondrial enzymes have the capacity to activate the pro-toxins involved in atypical myopathy. 
Using 16S rRNA sequencing, the authors identified significant differences in faecal microbial α-diversity, evenness and β-diversity, and notable differences within specific bacterial genera, between horses affected by atypical myopathy, their co-grazers, and unaffected toxin-free control horses. 
Further, the concentration of toxin-metabolite blood markers correlated with variation in faecal microbial composition.
Overall, these findings highlight a potential role of intestinal microbiota in the pathophysiology of atypical myopathy and prevention and therapeutic strategies.

This multi-centre study was conducted by researchers in Zurich, Munich, Pretoria, and Denmark and addressed the controversial topic of clinical leptospirosis in horses. The authors described the clinical presentation, diagnostic findings and outcome in cases of acute systemic leptospirosis, highlighting renal, pulmonary and hepatic effects. A multitude of non-specific clinical signs was observed, and the fatality rate was relatively high. In conclusion, the authors emphasised that leptospirosis should be considered as a differential diagnosis in horses with acute systemic inflammation and acute kidney injury, and advocated the combined use of serology and urine PCR to improve diagnostic sensitivity.

CARDIOLOGY

The cardiology team, in collaboration with the Department of Morphology, Imaging, Orthopaedics, Rehabilitation and Nutrition at Ghent University, has published this novel study investigating the potential arrhythmogenic substrate of the caudal vena cava. Following post-mortem dissection of 37 hearts from adult Warmblood horses without known cardiovascular disease, the authors described the consistent presence of myocardial sleeves extending into both the caudal and cranial vena cava, with marked inter-individual variation in size, shape, and distribution. Histological analysis revealed an heterogeneous myocardial fibre arrangement with fibro-adipose infiltration and myocardium-free islands; features known to promote slow conduction and re-entry. These findings support the concept that myocardial sleeves in the venae cavae may serve as an anatomical substrate for right-sided atrial tachyarrhythmias and represent potential targets for radiofrequency catheter ablation.

This multi-disciplinary study conducted at Ghent University described a novel procedure to gain access to the left side of the heart in horses, via atrial transseptal puncture. Using ultrasound-guided techniques and radiofrequency-assisted perforation of the fossa ovalis, the authors demonstrated that transseptal puncture is feasible in horses via jugular and transhepatic approaches without the use of fluoroscopy. The procedure was successful in 17 of 18 cases; transient atrial arrhythmias were observed in 13 cases. These findings support the potential of this technique for electrophysiological exploration of the equine left heart.

This interesting experimental and longitudinal observational study explored the feasibility of using an implantable loop recorder (ILR) designed for humans, to detect atrial fibrillation in horses. The first aim of the study was to validate and determine the sensitivity and specificity of the ILR device in the detection of atrial fibrillation in horses, whereby the device was implanted into 15 horses with induced atrial fibrillation, and 13 horses in sinus rhythm, both confirmed by surface electrocardiography. Secondly, to record the incidence of paroxysmal atrial fibrillation (pAF) in a separate population of 80 horses.
In the first population of 28 horses, the ILR device was able to record atrial fibrillation at all predetermined timepoints, with a sensitivity of 66.1% (consistent across all timepoints) and specificity of 99.99%.
In the second population of 80 horses, the incidence of paroxysmal atrial fibrillation recorded was 6.3%. The positive predictive value, calculated from 5/80 horses with detected pAF, ranged from 8% to 87%. 
The authors concluded that the ILR device reliably detected AF and that it can detect paroxysmal atrial fibrillation, making it a valuable diagnostic tool. However, Holter monitoring should be used alongside an ILR in horses with a body condition score > 6/9, since the device recorded false positive episodes of pAF in this subset of the studied population.

NEUROLOGY

Specialists from the University of Edinburgh recently published a study describing the ultrastructure of skeletal neuromuscular junctions in horses affected by equine grass sickness (EGS). The authors identified profound structural abnormalities; synaptic vesicle depletion, accelerated exocytosis, and degeneration of presynaptic terminals, using electron microscopy and morphometric techniques, The ultrastructural findings in EGS-affected horses  were markedly different from those observed at the skeletal  neuromuscular junctions of control horses, and also in a single case of equine botulism, indicating that EGS has a distinct pathogenic mechanism. These novel findings suggest that the causative toxin in equine grass sickness may target the skeletal neuromuscular junction and cause severe presynaptic dysfunction.

OTHERS

Colleagues from Utrecht University recently published this interesting article describing how a group of four horses selected for the Tokyo Olympic Games were acclimatised to the expected hot and humid climate conditions, while continuing their normal performance training. Three eventers and one para-dressage
horse were trained for 14 consecutive days in a heated indoor arena (32 ± 1 ◦C; 50–60% humidity) that simulated the environmental conditions expected in Tokyo. 
A standardised exercise test was performed on day 1 and repeated on day 14 of the acclimatisation period. Physiological parameters including heart rate, core body temperature, plasma lactate concentration, sweat production, and sweat electrolyte composition (sodium, potassium, chloride), were measured on day 1 and day 14.

Compared to the measurements taken on day 1, heart rate, rectal temperature and plasma lactate concentrations were lower on day 14, indicating improved cardiovascular efficiency and thermoregulation. In addition, three out of four horses exhibited reduced sweat loss overall and reduced loss of sodium and chloride in sweat. Overall, the results demonstrated that integrating a short period of heat acclimatisation into performance training may reduce thermal strain and improve cardiovascular efficiency in elite performance horses due to compete in hot climates, thereby improving welfare.