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Topic:Electrocardiography

Electrocardiography (ECG) in horses is a diagnostic tool used to assess the electrical activity of the heart. It involves recording the electrical impulses that govern heartbeats, providing insights into cardiac function and rhythm. This non-invasive method is useful for identifying arrhythmias, conduction disturbances, and other cardiac abnormalities in equine patients. Electrocardiography can be performed at rest or during exercise to evaluate cardiac performance under different physiological conditions. This page compiles peer-reviewed research studies and scholarly articles that explore the methodology, interpretation, and clinical applications of electrocardiography in equine health.
Three-dimensional electro-anatomical mapping of premature atrial complexes originating from the right atrial free wall and treatment by radiofrequency ablation in three horses.
Equine veterinary journal    September 9, 2025   doi: 10.1111/evj.70095
Buschmann E, Van Steenkiste G, Bulckens H, Schauvliege S, Decloedt A, van Loon G.Frequent premature atrial complexes (PACs) can increase the risk of atrial fibrillation or atrial tachycardia, and pharmacological therapy can be challenging. Objective: To report the use of three-dimensional electro-anatomical mapping of PAC originating from the right atrial free wall and treatment by radiofrequency ablation in three horses. Methods: Retrospective case report. Methods: Frequent premature atrial complexes (PACs) were diagnosed in three horses. Twelve-lead ECG and vectorcardiography suggested an origin in the right lateral free wall in two horses and the caudal right atrium in ...
Pilot Study: Heart Rate and Heart Rate Variability Indices in Mules Evaluated by 24-Hour Electrocardiogram.
Animals : an open access journal from MDPI    August 20, 2025   Volume 15, Issue 16 2438 doi: 10.3390/ani15162438
Maas LT, Morgan JM, Case J, Chell DD, McLean AK.Mules and donkeys are the 5th largest equine population in the U.S., yet basic information such as heart rate and arrhythmia prevalence in mules has not been described. Analysis of heart rate variability (HRV) provides valuable insight into physiologic and autonomic differences between mules, horses, and donkeys. We aimed to pilot the evaluation of heart rate and variability in a healthy population of mules using a 24 h electrocardiogram. Twenty-four-hour ambulatory electrocardiogram (aECG) recordings were collected from an athletic population of seven privately owned healthy mules in Northern...
A fitness tracker can be used interchangeably with a reference method for underwater single-lead electrocardiography but not heart rate variability analysis in swimming horses.
American journal of veterinary research    August 12, 2025   1-8 doi: 10.2460/ajvr.25.04.0113
Kisilevich Q, O'Connor SGP, Bayly WM, Léguillette R.To validate a single-lead ECG fitness tracker device (FT) against the reference multilead ECG recording device (RM) for heart rate (HR) and HR variability (HRV) monitoring of horses during routine swimming. Unassigned: 40 race-fit Thoroughbred racehorses were used for 5 days in May 2024. Surface ECG recordings were obtained simultaneously from the FT and RM devices in horses swimming 63.65 m across a pool. Electrocardiograms were reviewed and artifacts corrected when necessary, and correlations were analyzed between the 2 devices for HR and HRV parameters. Descriptive statistics and Bland-Altm...
Cardiac arrhythmia prevalence and risk factors in 24-h electrocardiograms of sedentary horses.
Equine veterinary journal    July 18, 2025   doi: 10.1111/evj.14543
Maas LT, Louie EW, Finno CJ, Donnelly CG, Stern JA, Hill AE, Morgan JM.Cardiac arrhythmias are common in horses, but their clinical relevance remains controversial. Objective: To describe prevalence and identify risk factors for arrhythmias that may warrant additional screening in a sedentary mixed-breed population of horses. Methods: Prospective cross-sectional. Methods: Ninety-four clinically healthy, university-owned, sedentary horses underwent 24-h ambulatory electrocardiograms and echocardiograms. Potential risk factors were recorded for all horses. Affected individuals were defined as those with >1 supraventricular premature complex/h or with any ventric...
Orthodromic Atrioventricular Reentry Bradycardia and Tachycardia Caused by an Accessory Pathway in Horses.
Journal of veterinary internal medicine    July 17, 2025   Volume 39, Issue 4 e70175 doi: 10.1111/jvim.70175
Buschmann E, Easton-Jones C, Van Steenkiste G, De Wilde H, Roberts V, Durando M, Decloedt A, Marr C, van Loon G.Accessory pathways (APs) are muscular bundles directly connecting the atria and ventricles, bypassing the atrioventricular (AV) node-His-Purkinje system. Anterograde conduction along the AP results in ventricular preexcitation. A retrograde conducting AP allows ventriculo-atrial (VA) conduction, creating a reentry circuit that mediates orthodromic atrioventricular reentry tachycardia (OAVRT). This condition is well described in humans and small animals, but has not been reported previously in horses. Objective: Describe clinical and electrocardiographic findings of horses with retrograde AP co...
Application of Acoustic Cardiography in Assessment of Cardiac Function in Horses with Atrial Fibrillation Before and After Cardioversion.
Animals : an open access journal from MDPI    July 7, 2025   Volume 15, Issue 13 1993 doi: 10.3390/ani15131993
Schneider MJ, Piotrowski IL, Junge HK, van Steenkiste G, Vernemmen I, van Loon G, Schwarzwald CC.Left atrial mechanical dysfunction is common in horses following the treatment of atrial fibrillation (AF). This study aimed to evaluate the use of an acoustic cardiography monitor (Audicor) in quantifying cardiac mechanical and hemodynamic function in horses with AF before and after treatment and to correlate these findings with echocardiographic measures. Twenty-eight horses with AF and successful transvenous electrical cardioversion were included. Audicor recordings with concomitant echocardiographic examinations were performed one day before, one day after, and two to seven days after card...
Ventriculophasic response in a horse with atrioventricular block.
Journal of veterinary cardiology : the official journal of the European Society of Veterinary Cardiology    May 17, 2025   Volume 60 46-49 doi: 10.1016/j.jvc.2025.05.005
Liu J, Baumwart R, Kwon S.Ventriculophasic response (VR) in atrioventricular nodal (AVN) block is characterized by a shortening of the sinoatrial cycle length when a QRS complex is interposed between two P waves. This has been well documented in humans and dogs with AVN blocks but not in horses. Herein, we describe a horse with second-degree AVN blocks and constant PR intervals that exhibited 5:3 conduction and suspected VR at rest but less consistently after submaximal exercise. Proposed VR mechanisms include (1) inhibition of the Bezold-Jarisch reflex from reduced end-systolic volume during ventricular contraction; (...
Can Acute Neurological Disease Cause Cardiomyopathy in Horses?
Animals : an open access journal from MDPI    May 16, 2025   Volume 15, Issue 10 doi: 10.3390/ani15101447
Vitale V, Velloso Álvarez A, de la Cuesta-Torrado M, Neira-Egea P, Vandecandelaere M, Tee E, Gimeno M, van Galen G.In human medicine, neurological diseases have been associated with transient cardiac abnormalities. In horses, myocardial disease is rarely diagnosed and has been associated with a wide variety of causes. The aim of this article is to describe three horses with no previous cardiac disease, which all developed severe cardiomyopathy following neurological disease. A 5-year-old Shetland pony stallion was diagnosed with cardiomyopathy with arrhythmias following an episode of seizures caused by an accidental intra-arterial xylazine injection. A 20-year-old crossbred mare was hospitalised for an ope...
Physiological and behavioral parameters of pain and stress in mares during and after transvaginal ultrasound-guided follicular aspiration.
Frontiers in veterinary science    April 9, 2025   Volume 12 1574351 doi: 10.3389/fvets.2025.1574351
Van den Branden E, Salamone M, Broothaers K, Peere S, Polfliet E, Dewulf M, Van Steenkiste G, van Loon G, Smits K, Govaere J.The use of transvaginal ultrasound-guided follicle aspiration (TVA) for oocyte collection has become a widely used procedure in horses for embryo production (IVEP). The TVA procedure is characterized by various manipulations, which are physical restraint, perineal preparation, transrectal palpation, insertion of an intravaginal device, and needle punctures. These repeated transvaginal and transovarian punctures have raised concerns about their potential effects on mare welfare. Our study aimed to investigate the effects of TVA manipulations, and especially puncturing, on pain and stress in ma...
The effects of a plant-based and a plant- and marine-based n-3 oil supplement on behavioural reactivity, heart rate variability, and plasma fatty acid profile in young healthy horses.
Journal of animal science    April 8, 2025   skaf117 doi: 10.1093/jas/skaf117
Hartwig S, Rankovic A, McCrae P, Gagliardi K, Burron S, Ellis J, Ma DWL, Shoveller AK.Behavioural reactivity in horses poses a welfare and safety risk to both the horse and the handler, however, beneficial effects have been observed when dietary fat is increased in replacement of sugar. Supplementation with the fatty acids (FA) eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) appear to improve negative behaviours in rodents and humans, but the effect of α-linolenic acid (ALA), EPA, and DHA, specifically, on reactivity in horses is unknown. The objective of this study was to evaluate the effects of camelina oil (CAM; ALA-enriched) and a mix of camelina and algal oil (ALG; ...
Best practices for physiological data collection in youth with autism and co-occurring mental health diagnoses: Implications for human-animal intervention research.
MethodsX    March 27, 2025   Volume 14 103284 doi: 10.1016/j.mex.2025.103284
Smith CM, Weimann K, Widick M, Merritt T, Christensen H, Siegel M, Pan Z, Gabriels RL.The purpose of this paper is to serve as a catalyst for the human-animal interaction research field to improve scientific rigor and accelerate the knowledge of field-based physiological responses during equine-assisted services in youth with autism spectrum disorder. This paper outlines the best practices for collecting and analyzing electrocardiogram and electrodermal activity in youth with autism spectrum disorder, utilized during a 10-week therapeutic horseback riding intervention.•Motivation strategies such as device choice, reward systems, and a visual schedule should be implemented to ...
Association of heart rate variability, exercise intensity and exercising arrhythmias with competition results in eventing horses.
Equine veterinary journal    February 26, 2025   doi: 10.1111/evj.14491
Navas de Solis C, Ramseyer A, Stefanovski D, Haughan J, Solomon CJ, Kirsch K.Exercising arrhythmias are common in horses participating in eventing competitions. Heart rate variability (HRV) and a specific measure of the degree of heart rate fluctuation (Detrended Fluctuation Analysis alpha1; DFA-α1) are proposed as exercise intensity and fatigue markers. Objective: (1) To describe exercising arrhythmias and DFA-α1 values during 2-4* level eventing cross-country competitions in horses from two European countries; (2) to identify associations between exercising arrhythmias, DFA-α1 and competition results and (3) to evaluate whether markers of the intensity of exercise...
Heart rate variability responses of horses and veterans with post-traumatic stress disorder to ground-based adaptive horsemanship lessons: a pilot study.
Translational animal science    February 12, 2025   Volume 9 txaf019 doi: 10.1093/tas/txaf019
Rankins EM, Faremi BE, Hartmann K, Quinn A, Posada-Quintero HF, McKeever KH, Malinowski K.Heart rate variability (HRV) can be measured as an indicator of autonomic nervous system (ANS) balance and thus, stress and affective arousal. Mixed results have been reported in the limited literature addressing the effects of equine-assisted services (EAS) on HRV in the human and horse participants. The aims of the present study were to determine the effects of ground-based adaptive horsemanship (AH) lessons on veterans' and horses' HRV during weekly lessons as well as veterans' resting HRV outside of lessons. Veterans with post-traumatic stress disorder (PTSD) were randomly assigned to 8 w...
Examining the arrhythmogenicity of dobutamine when used in conjunction with isoflurane in horses: A retrospective study at a single university teaching hospital.
The Veterinary record    January 28, 2025   e5123 doi: 10.1002/vetr.5123
Ishihara T, Nieves E, Reed R, Hofmeister E.Dobutamine is used to treat hypotension in isoflurane-anaesthetised horses but may produce arrhythmias. Halothane is a volatile anaesthetic that was, historically, widely used in horses, but in one study, 56 of 200 halothane-anaesthetised horses (28%) developed arrhythmias after dobutamine administration. Although isoflurane has largely replaced halothane, it is unknown how isoflurane and dobutamine interact in the development of arrhythmias. Methods: The medical records of horses undergoing general anaesthesia at the University of Georgia Veterinary Teaching Hospital in 2015 were reviewed ret...
Plasma Cardiac Troponin-I Concentration in Normal Horses and in Horses with Cardiac Abnormalities.
Animals : an open access journal from MDPI    January 3, 2025   Volume 15, Issue 1 doi: 10.3390/ani15010092
Foreman JH, Tennent-Brown BS, Oyama MA, Sisson DD.Cardiac troponin-I (cTnI) is a highly sensitive and specific marker of myocardial injury detectable in plasma by immunoassay techniques. Inclusion criteria over a 3-year period required a diagnosis of cardiac disease accompanied by electrocardiographic (ECG) and cardiac ultrasound examinations (n = 23) in adult horses (≥2 years of age). A second group of normal adult ponies (n = 12) was studied as a reference group. Heparinized jugular venous blood samples were collected and centrifuged within 30 min, and the plasma was separated and frozen at -70 °C for subsequent batched cTnI analysis. Th...
A consort-guided randomized, blinded, controlled clinical trial on the effects of 6 weeks training on heart rate variability in thoroughbred horses.
Journal of veterinary internal medicine    December 10, 2024   Volume 39, Issue 1 e17253 doi: 10.1111/jvim.17253
Santosuosso E, Léguillette R, Shoemaker S, Baumwart R, Temple S, Hemmerling K, Kell T, Bayly W.Fitness assessment of horses remains challenging. Heart rate variability (HRV) can be used to monitor human athlete's training, but its value is unknown in horses. Objective: The linear domain HRV variables are affected by fitness. Methods: Twelve healthy untrained thoroughbreds were randomly split into a training group (6 weeks of incremental racetrack training) and a control group (no training). Methods: Linear domain HRV variables were analyzed (high frequency [HF], low frequency [LF], their normalized units [Hf, Lf], root mean square of successive differences between beats [RMSSD], Poinc...
Electrocardiograms from different types of exercise in Eventing horses with and without cardiac signs.
Equine veterinary journal    December 4, 2024   Volume 57, Issue 4 991-1000 doi: 10.1111/evj.14449
Navas de Solis C, Solomon C, Durando M, Stefanovski D.Exercising arrhythmias can be clinically irrelevant or associated with poor performance, collapse and sudden cardiac death. Objective: To test if readable exercising ECGs can be recorded by grooms or riders and to describe arrhythmias in ECGs from different types of exercise in Eventing horses and investigate associations with type of workout, the presence of previous cardiac signs and intensity of exercise. Methods: Cohort study. Methods: Single lead exercising ECGs were obtained by riders or grooms during training and competition from a convenience sample of horses in training for Eventing c...
Caudal vena cava isolation using ablation index-guided radiofrequency catheter ablation (CARTO™ 3) to treat sustained atrial tachycardia in horses.
Journal of veterinary internal medicine    November 30, 2024   doi: 10.1111/jvim.17251
Buschmann E, Van Steenkiste G, Vernemmen I, Demeyere M, Schauvliege S, Decloedt A, van Loon G.Myocardial sleeves of the caudal vena cava are the predilection site for atrial tachycardia (AT) in horses. Caudal vena cava isolation guided by the ablation index, a lesion quality marker incorporating power, duration and contact force, might improve outcome. Objective: Describe the feasibility and outcome of caudal vena cava isolation using ablation index-guided radiofrequency catheter ablation (RFCA) to treat AT in horses. Methods: Ten horses with sustained AT. Methods: Records from 10 horses with sustained AT treated by three-dimensional electro-anatomical mapping and ablation index-guided...
A new smartphone-based digital stethoscope featuring phonocardiography and electrocardiography in adult horses.
Veterinary research communications    November 27, 2024   Volume 49, Issue 1 43 doi: 10.1007/s11259-024-10584-w
Bindi F, Bozzola C, Vezzosi T, Zucca E, Caivano D, Freccero F, Sala G, Sgorbini M.Smartphone-based technology is increasingly used in veterinary medicine as a complementary tool for cardiac auscultation and ECG recording. This prospective observational study evaluates a digital stethoscope (DS) that consists of simultaneous phonocardiographic and one-lead ECG recording (dECG) in adult horses, comparing it with auscultation using a conventional stethoscope (CS) and reference base-apex ECG (rECG). A total of 104 horses underwent cardiac auscultation using CSs and DSs to detect arrhythmias and murmurs. Audio and dECG were acquired using the DS. The rECG tracings were also reco...
Smartphone-based ECG assessment of heart rhythm at birth in healthy foals born after spontaneous or induced parturition: is there a potential difference?
Veterinary research communications    November 23, 2024   Volume 49, Issue 1 31 doi: 10.1007/s11259-024-10576-w
Petrucelli M, Sgorbini M, Castagnetti C, Lanci A, Mariella J, Marmorini P, Freccero F.Background- Subclinical electrophysiological derangements occur at birth in foals. Smartphone-based ECG (spECG) is practical tools to assess heart rhythm and was recently validated in foals. Objectives-To assess the heart rate (HR) and rhythm at birth in clinically healthy foals born after spontaneous and induced parturition using a spECG. Animals- Newborn healthy foals born after at term spontaneous (SF) or induced foaling (IF). Methods- Cohort study. In SF and IF groups, a spECG was performed immediately at birth (T0) and after 5 min (T5). SpECG tracings were selected for quality. HR was ma...
Lesion size index-guided radiofrequency catheter ablation using an impedance-based three-dimensional mapping system to treat sustained atrial tachycardia in a horse.
Equine veterinary journal    October 21, 2024   doi: 10.1111/evj.14424
Buschmann E, Van Steenkiste G, Vernemmen I, Demeyere M, Schauvliege S, Decloedt A, van Loon G.Sustained atrial tachycardia at an atrial rate of 191/min on the surface ECG was detected in a 6-year-old Warmblood mare. The vectorcardiogram obtained from a 12-lead ECG suggested a caudo-dorsal right atrial origin of the arrhythmia. Impedance-based three-dimensional electro-anatomical mapping, using the EnSite™ Precision Cardiac Mapping System revealed a clockwise macro-reentry around a line of conduction block in the caudomedial right atrium. Ten radiofrequency applications were applied to isolate the caudal vena cava myocardial sleeves at a power of 35 W and mean contact force of 14 ...
Quadricuspid aortic valve in a 16-year-old Quarter horse.
Journal of equine veterinary science    September 20, 2024   Volume 142 105199 doi: 10.1016/j.jevs.2024.105199
Caivano D, Cicogna M, Orvieto S, Spitale D, Porciello F.A 16-year-old horse, 400 kg, male, Quarter horse gelding was examined for a cardiac murmur that had not been previously heard. Physical examination revealed a regularly irregular pulse and a grade III/VI, decrescendo, diastolic murmur with a point of maximum intensity over the left heart base. Base-apex standard electrocardiographic examination at rest showed sinus rhythm with second-degree atrio-ventricular blocks. Echocardiography identified the presence of four aortic valve cusps, two equal larger and two unequal smaller cusps. Color flow Doppler examination showed a diastolic regurgitant j...
Heart rate variability in horses with and without severe equine asthma.
Equine veterinary journal    September 14, 2024   doi: 10.1111/evj.14414
Nyerges-Bohák Z, Kovács L, Povázsai Á, Hamar E, Póti P, Ladányi M.Equine asthma in severe form (severe equine asthma [sEA]) shares remarkable similarities with human asthma. Human studies detected changes in the autonomic nervous system function in asthmatic patients based on heart rate variability (HRV) analysis. Methods: Observational study. Objective: To investigate the relationship between sEA and HRV in horses. Methods: Twenty horses diagnosed with sEA and 20 asymptomatic (non-sEA) horses were investigated. SEA horses showed clinical signs. The RR intervals of the ECG were recorded for 1 h at rest between 9 AM and 11 AM using a heart rate (HR) mon...
Unveiling directional physiological coupling in human-horse interactions.
iScience    August 31, 2024   Volume 27, Issue 9 110857 doi: 10.1016/j.isci.2024.110857
This research investigates the human-horse bond, aiming to unveil the physiological mechanisms regulating interspecies interactions. We hypothesized observing a physiological synchronization in human-horse dynamics, akin to human interactions. Through time-frequency Granger causality analysis of heart rate variability (HRV) and behavioral data, this study reveals the establishment of bidirectional synchronization in HRV between humans and horses. The coupling directionality is influenced by behavior and familiarity. In exploration scenarios led by horses, bidirectional interactions occur, part...
Intravenous administration of quinidine and metoprolol for treatment of atrial fibrillation in 2 neonatal foals.
Journal of veterinary internal medicine    August 30, 2024   Volume 38, Issue 5 2783-2789 doi: 10.1111/jvim.17164
Leduc L, Abraham M, Slack J.Atrial fibrillation (AF) is a rarely reported arrhythmia in otherwise healthy newborn foals, with a single case of cardioversion using procainamide administration described in the literature. Two neonatal Thoroughbred colts were presented to an equine hospital because of an irregularly irregular tachyarrhythmia and poor latching when trying to nurse. History, physical examination, and initial diagnostic testing including ECG and echocardiography confirmed AF without structural heart disease. The 1st foal converted into normal sinus rhythm after treatment with IV metoprolol and quinidine. The 2...
Einthoven’s triangle adapted for horses: Proposal for the Delta configuration.
Journal of veterinary internal medicine    August 28, 2024   doi: 10.1111/jvim.17179
Paulussen E, Van Steenkiste G, Hermans BJM, Decloedt A, van Loon G, Delhaas T.Reliable ECGs are crucial for diagnosing arrhythmias, yet a lack of standardization impedes arrhythmia diagnosis and treatment in horses. Objective: To objectively determine an optimal position of Einthoven's triangle for ECG recordings in horses at rest, which can form the basis for standardized ECG recording and improve diagnosis and treatment of arrhythmias. Methods: The study involved 72 healthy, warmblood horses aged between 3 and 20 years. Methods: In view of future 12-lead studies and vectorcardiography, requiring an orthogonal system, Einthoven's triangle was positioned around the he...
Long-term use of an implantable loop recorder for ECG recording in horses.
Acta veterinaria Hungarica    August 22, 2024   Volume 72, Issue 3 178-185 doi: 10.1556/004.2024.01075
Kovács S, Bodó G, Tóth FZ, Néder L, Bakos Z.Potential arrhythmias recorded by cardiac monitors using the built-in human algorithm are as follows: total number of episodes, ventricular tachycardia, asystole, bradycardia, atrial tachycardia, atrial fibrillation and the percentage of time spent in atrial tachycardia or atrial fibrillation. Long-term use of an insertable cardiac monitor (loop recorder) has been reported in one horse earlier, but its accurate role as a diagnostic tool is still unclear. The aim of the present study was to investigate the long-term applicability of the Reveal XT cardiac monitor for recording cardiac arrhythmia...
Stress Responses in Horses Housed in Different Stable Designs during Summer in a Tropical Savanna Climate.
Animals : an open access journal from MDPI    August 4, 2024   Volume 14, Issue 15 2263 doi: 10.3390/ani14152263
Poochipakorn C, Wonghanchao T, Sanigavatee K, Chanda M.Single-confinement housing can pose welfare risks to domestic horses. This study investigated horses' stress responses when confined to single stalls in different stable designs in a tropical savanna region to address a gap in the literature. In total, 23 horses were assigned to a stable with a central corridor and solid external walls (A) (N = 8), a stable with one side corridor and solid external walls (B) (N = 6), or a stable with a central corridor and no solid external walls (C) (N = 9). Air velocity, relative humidity, air temperature, and noxious gases were measured inside the stables, ...
Intracardiac ultrasound-guided transseptal puncture in horses: Outcome, follow-up, and perioperative anticoagulant treatment.
Journal of veterinary internal medicine    July 31, 2024   Volume 38, Issue 5 2707-2717 doi: 10.1111/jvim.17158
Vernemmen I, Buschmann E, Van Steenkiste G, Demeyere M, Verhaeghe LM, De Somer F, Devreese KMJ, Schauvliege S, Decloedt A, van Loon G.Cardiac catheterizations in horses are mainly performed in the right heart, as access to the left heart traditionally requires an arterial approach. Transseptal puncture (TSP) has been adapted for horses but data on follow-up and closure of the iatrogenic atrial septal defect (iASD) are lacking. Objective: To perform TSP and assess postoperative complications and iASD closure over a minimum of 4 weeks. Methods: Eleven healthy adult horses. Methods: Transseptal puncture was performed under general anesthesia. Serum cardiac troponin I concentrations were measured before and after puncture. Wee...
Workload and spirometry associated with untethered swimming in horses.
BMC veterinary research    July 19, 2024   Volume 20, Issue 1 327 doi: 10.1186/s12917-024-04143-3
Leguillette R, McCrae P, Massie S, Filho SA, Bayly W, David F.Swimming has been used empirically for rehabilitation and conditioning of horses. However, due to challenges imposed by recording physiological parameters in water, the intensity of free swimming effort is unknown. Objective: Measure the physiological workload associated with untethered swimming in horses. Five fit Arabian endurance horses were assessed while swimming in a 100 m-long indoor pool. Horses were equipped with a modified ergospirometry facemask to measure oxygen consumption (V̇O) and ventilatory parameters (inspired/expired volumes, V, V; peak inspiratory/expiratory flows, PkV, P...