The physiology of horses encompasses the study of the biological functions and processes that occur within the equine body. This includes the examination of various systems such as the cardiovascular, respiratory, musculoskeletal, digestive, and nervous systems. Understanding equine physiology is essential for comprehending how horses adapt to different environmental conditions, perform physical activities, and respond to health challenges. Research in this field often focuses on the mechanisms of energy metabolism, thermoregulation, and muscle function during exercise, as well as the physiological responses to stress and disease. This page compiles peer-reviewed research studies and scholarly articles that explore the diverse aspects of equine physiology, providing insights into the biological processes that support the health and performance of horses.
Avison A, Physick-Sheard PW, Pyle WG.This paper reviews the myocardial substrate of horses relative to that of humans and discusses the utility of performance horses as a model of exercise-associated cardiac arrhythmias and sudden cardiac death in athletes. The coronary circulation is similar between the species while coronary artery anomalies and myocardial bridging appear to only be associated with athletic mortality in human athletes and not in performance horses. There are subtle differences in the histology of the sinus and atrioventricular nodes, of unknown clinical significance, while the His bundle is more highly innervat...
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; (...
Liedtke AM, Meijer H, Horstmann S, von Reitzenstein C, Rump I, Kirsch K.Eventing is an Olympic equestrian discipline comprising dressage, cross-country, and show jumping, with the cross-country phase imposing the greatest physical demands on horses. This study presents a composite model to estimate energy expenditure during the cross-country phase, integrating physiological data (heart rate-derived VO2 and lactate-based anaerobic estimates) with external workload indicators (GPS-derived speed, elevation, and course complexity). Model development was based on 691 rides from 256 horses across 232 events at 2-star to 5-star competition levels. The analysis showed tha...
Kiełbik P, Witkowska-Piłaszewicz O.Iron is unquestionably an essential element of physical performance for horses, just as it is for many other animals, including humans. Although post-exercise equine iron deficiency is not a common problem, recent studies showed that equine athletes may be considered a model for human exercise physiology. Sports anemia among human athletes is a common nutritional issue and remains one reason for poor physical fitness. Thus, this study area needs comprehensive knowledge since iron homeostasis changes in equine athletes remain unrecognized. The current review aims to summarize studies describing...
Kroschel L, Pilger F, Aurich J, Nagel C, Aurich C.Horses in training are often stabled individually, but this is increasingly questioned. We have investigated the effects of different stabling systems in Warmblood stallions during a 12-week pretraining programme. Stallions were 24 months old and housed either in a group stable (Group 24, n = 9) or in individual boxes (Box 24, n = 10), or they were 30 months of age and housed in individual boxes (Box 30, n = 10). Cortisol, heart rate, heart rate variability (HRV), body development, injuries and selected behaviour patterns were analysed (1) at transfer from pasture to stable and (2) the...
Bugno-Poniewierska M, Bielecka M, Pietras N, Kij-Mitka B, Podstawski Z, Długosz B.The Hucul horse is a Polish primitive breed with a small population size, which highlights the importance of preserving the genetic resources. The cryopreservation of semen is essential for creating gene banks, but its effect on the acrosome reaction in Hucul stallions has not yet been investigated. The acrosome reaction is one of the most important physiological events associated with the fertilization process. Therefore, our goal was to determine the level of acrosome reaction in chilled and frozen/thawed Hucul stallion semen using the FluoAcro test and the SCA semen analysis system. We foun...
MacKechnie-Guire R, Clayton H, Byström A, Marlin D, Haussler K, Latif S, Blum N, le Jeune SS, Wanless M, Egenvall A.Laterality or sidedness in the horse is commonly addressed as part of the horse's training. An international online survey regarding horse and rider sidedness and asymmetry was conducted, with 2304 useable responses. Confidence intervals (95%) were used to evaluate if some response options were chosen more frequently. Discounting answers of 'not sure' or 'not applicable', the right fore hoof was more often perceived to be more upright (22%) than the left (15%), and the left shoulder was more prominent (24%) more often than the right (17%), whilst most respondents reported no difference. Both l...
Wonghanchao T, Sanigavatee K, Petchdee S, Chettaratanont K, Thongyen T, Wanichayanon B, Poochipakorn C, Chanda M.The physiological capabilities of horses begin to decline after they reach 15 years of age. However, some exceptionally talented horses can continue their sports careers beyond this age, raising concerns about their welfare. This study investigated animal welfare by observing resting heart rate (HR) and heart rate variability (HRV) metrics in geriatric horses participating in similar training or physical activities compared to younger adult horses over 30 min periods. Forty-six horses of varying ages and activity levels were divided into four groups, including horses under 15 years practising ...
Bailey VN, Gilbert BM, Vetter M, Oberhaus EL.The mechanism by which photoperiod influences the hypothalamic-pituitary-gonadal (HPG) axis and regulates seasonal reproduction in horses has yet to be fully elucidated. The hypophyseal pars tuberalis (PT) has been indicated as a critical site for the transduction of melatonin signals through melatonin-responsive, PT-specific cells that produce thyroid-stimulating hormone (TSH) in many mammalian species. However, this has yet to be investigated in horses. The objective of this study was to explore the interaction of melatonin and thyroid-stimulating hormone in the equine HPG axis. Pituitaries ...
Mendoza Flores JE, Terrazas A, Lara Sagahon AV, Aleman M.Parasympathetic tone activity (PTA) and its association with behavior in conscious versus anesthesia in horses are unknown. Objective: To study PTA, heart rate (HR), minimum alveolar concentration (MAC), and mean arterial pressure (MAP) during castration under anesthesia. To study PTA, HR, Horse Grimace Scale (HGS), locomotor activity (LA), and behavior in conscious horses before and after castration. Methods: Pilot study including seven healthy adult horses. After habituation (days 1, 2, and 3), PTAm, HR, HGS, LA, and behavior were investigated during pre-surgery (days 4-, 5-, and one-hour pr...
Valenchon M, Reigner F, Lefort G, Adriaensen H, Gesbert A, Barrière P, Gaude Y, Elleboudt F, Lévy I, Ducluzeau C, Dupont J, Lainé AL, Uszynski I....Social interactions shape both the physiological and behavioural development of offspring, and poor care/early caregiver loss is known to promote adverse outcomes during infancy in both animals and humans. How affiliative behaviours impact the future development of offspring remains an open question. Here, we used Equus caballus (domestic horse) as a model to investigate this question. By coupling magnetic resonance imaging, longitudinal biobehavioural assessments and advanced multivariate statistical modelling, we found that prolonged maternal presence during infancy promotes the maturation o...
Bindi F, Cingottini D, Sorvillo B, Sala G, De Marchi L, Monni G, Celardo S, Bonelli F, Sgorbini M.During the perinatal period, neonates experience a sudden increase in oxygen exposure, predisposing them to oxidative stress. Objective: This prospective, in vivo study aimed to evaluate biomarkers of oxidative stress and antioxidant defence in healthy neonatal foals during the first 48 hours of life. Methods: Ten Standardbred foals were enrolled. Blood samples were collected at birth, 24 hours, and 48 hours after birth and analyzed for biomarkers using spectrophotometry assays. Statistical analysis was performed using non-parametric tests and linear regression. Results: The results revealed s...
Yuan X, Yao X, Zeng Y, Wang J, Ren W, Wang T, Li X, Yang L, Yang X, Meng J.The effects of physical exercise on protein expression and metabolites in the plasma exosomes of horses are not yet clear. This study aims to elucidate the effects of exercise training on the expression of plasma extracellular vesicle proteins and metabolites in horses through multi-omics analysis, providing reference indicators for the training and performance evaluation of horses. Methods: Eight healthy 3-year-old horses were selected for the study, with four untrained horses as the control group and four trained horses as the training group. After conducting proteomic and metabolomic an...
Mlyneková E, Zaťko S, Halo M, Imrich I, Halo M.This study aimed to examine the seasonal dynamics of non-structural carbohydrates in pasture and their relationship to metabolic indicators in horses with a history of laminitis. Thirty Hucul mares were divided into a laminitis group (LG, = 15) and a control group (CG, = 15). Insulin, glucose, fructosamines concentrations and body weight were monitored during four sampling periods (S0-S3), while pasture variables were analyzed during three periods (S1-S3). The concentration of water-soluble carbohydrates was highest in May (126.8 g/kg DM) and measured lower in October (57.9 g/kg DM), while s...
Henshall C, McGreevy P, Shea G, Doherty O, Christensen JW, Fenner K, Warren-Smith A, McLean A.The use of horses for sport is under scrutiny due to evidence that common practices such as tight nosebands may impair horse welfare. Restrictive nosebands prevent horses from performing normal comfort behaviour such as coughing and yawning. To address these concerns, the International Society for Equitation Science (ISES) developed a noseband tightness-checking device, the ISES "taper gauge," along with a validated method that assesses how far the device can be inserted beneath the noseband at the dorsal midline of the nasal planum. However, citing concerns about the reliability of dorsal mid...
Jung Y, Yoon M.Oxytocin (OXT) plays a crucial role in regulating the serotonin (5-HT) system and behavior. Although previous studies have reported significant relationships among OXT, 5-HT, and behavioral responses, the effects of OXT on 5-HT concentrations and behavioral traits in horses remain poorly understood. This study aimed to investigate the effects of intravenous OXT administration on plasma 5-HT concentrations and trainability in horses. A crossover design was employed using eight horses, each receiving either a 10-IU intravenous dose of OXT or normal saline. Blood samples were collected at baselin...
Hodgson E, Romano TR, Stewart A, Bond S, Wise J.The pathogenesis of gastric ulceration is not well understood in foals, and its relationship with gastric acidity requires further investigation. A wireless capsule, designed for intraesophageal pH monitoring in humans, was adapted to measure intragastric pH in adult horses. Objective: To (1) determine the feasibility of wireless intragastric pH measurement in foals; (2) determine capsule attachment duration; and (3) describe the intragastric pH profiles recorded. Methods: Eight healthy foals aged 24-98 days. Methods: Prospective interventional study. Capsules were attached to the glandular g...
Avison A, Pyle WG, Sears W, Physick-Sheard PW.Sudden cardiac death is a leading cause of athletic death in both humans and horses, making racehorses a potentially valuable model for investigating sudden cardiac death. Cardiac restitution ratio (QT/TQ interval) is used to assess arrhythmia risk in humans, but investigations in athletes are scarce. The objective was to characterize QT interval and cardiac restitution ratio in Thoroughbred racehorses during maximal effort. Automated restitution analysis was performed using 2709 pairs of cardiac cycles from 30 Thoroughbred horses during races. Cardiac cycles were obtained during: pre-race; ac...
Valera M, Encina A, Sánchez-Guerrero MJ, Rodríguez-Sainz de Los Terreros A, Bartolomé E.Behavioral and emotional reactivity assessment in sport horses is essential for optimizing their management and sports performance, particularly in equestrian disciplines such as Dressage. This study investigates, in Pura Raza Española (PRE) horses, the association between facial hair whorl (FHW) patterns, behavioral traits, and physiological stress responses using ocular temperature (OT) assessed with infrared thermography as, an objective, non-invasive physiological stress indicator. Unassigned: A total of 98 male PRE horses, aged 4-6 years old and all gray coated, were evaluated during the...
Raidal SL, van Diggelen M, Catanchin CSM, Lehmann HS, Quinn CT.Noninvasive ventilation (NIV) provides effective respiratory support in foals, but face masks are poorly tolerated and associated with hypercapnia. Bi-nasal prongs might be a more effective device interface in foals. Objective: To compare bi-nasal prongs and masks for NIV in foals with pharmacologically induced respiratory insufficiency. Methods: Six healthy foals. Methods: In a randomized cross-over study, sedated foals received NIV delivered by mask or bi-nasal prongs, with the treatment repeated using the alternative device interface after a 3-day rest period. After periods of spontaneous v...
Takahashi K, Shirai T, Mukai K, Ebisuda Y, Sugiyama F, Yoshida T, Kitaoka Y.While exercise performance deteriorates in hot environments, heat stress may contribute to exercise-induced adaptations in skeletal muscle. In this study, we assessed transcriptional profiles of equine skeletal muscle following 3 min of high-intensity exercise (at the speed eliciting their maximal oxygen uptake) in cool [wet bulb globe temperature (WBGT) 15°C] or hot (WBGT 30°C) conditions. Differential gene expression was identified using DESeq2 (false discovery rate cutoff: 0.05, minimal fold change: 1.5). At 4 h after exercise, RNA-seq identified 176 and 156 genes that were differentially...
Ishimaru M, Kume K, Murase H, Sato F, Matsui A, Ohmura H, Taya K.Thoroughbreds born early in the year are believed to have an advantage in racing. However, the development of endocrine functions in early-born foals in the cold winter climate is unclear. The present study was conducted to elucidate the effect of birth month on the development of endocrine function in Thoroughbred foals born from February to May in Hokkaido by comparing hypothalamic-pituitary axis, adrenal and thyroid functions from birth to 24 weeks of age. Eighty-seven Thoroughbred foals were used to compare the changes in circulating luteinizing hormone (LH), follicle-stimulating hormone (...
Maria Feitosa Ribeiro L, Bersot Gomes JV, Hernando Ortiz Vega W, da Silva Alves A, Netto Machado M, Junio Wutke L, Raquel Quirino C....Stallion breeding is mostly based on desirable phenotypic traits, with little consideration for semen quality. Objective: To identify relationships among semen parameters in stallions using a non-invasive, integrative approach across summer and winter seasons. Methods: Twenty-four stallions were evaluated, in which semen collections, testicular thermography, and Doppler velocimetry of the testicular artery by Doppler ultrasonography were performed, in addition to the measurement of physiological, environmental, and heat stress parameters, both in winter (coat weather) and summer (T-shirt weath...
Scoggin KE, Adlan F, Fedorka CE, Rakha SI, Stout TAE, Troedsson MHT, Ali HE.The insulin-like growth factor (IGF) system regulates implantation, placental development, and angiogenesis in eutherian mammals. However, little is known about the changes in this system in equine placenta (chorioallantois; CA) and the endometrium (EN) during pregnancy, or the relationship to vascular endothelial growth factor () expression. The current study investigated the expression of the IGF system components, namely the ligands ( and ), their receptors (, , and ), and their binding proteins ( and s) in equine CA at 45 days, 4, 6, 10, and 11 months of gestational age (GA) and immediatel...
Atayde MF, Vidondo B, Bruckmaier R, Freymond SB, Sieme H, Rey-Kaeser R, Burger D.In-hand breeding involving restraint methods is likely the most common practice in the horse breeding industry worldwide. However, welfare issues that arise from such management have not been investigated in detail. Objective: (1) To investigate whether the mares show increased stress responses during in-hand breeding using (a) a lip twitch and (b) hobbles. (2) To evaluate if the use of restraint methods influences the mare's expression of oestrous behaviour. Methods: Intra-individual cross-over design. Methods: Six Franches-Montagnes stallions and 10 warmblood mares were used in these experim...
Roth LSV, McGreevy P.To improve human-horse interactions and reduce the risk of injury, it is essential to adopt an equi-centric perspective that prioritizes how horses perceive their environment. This review focuses on the equine visual system, both because it is the most studied of the horse's senses and because misunderstandings about how horses see can lead to unsafe or unsustainable handling. By applying two complementary frameworks, namely Tinbergen's Four Questions and the Five Domains model, we examine equine vision from both a biological and a welfare-oriented perspective. We explore the anatomical and fu...
Paganelli GC, Schott HC.Small intestinal (SI) distension and gastric reflux (GR) are common in horses with mechanical and functional ileus. Removal of GR results in fluid/ion losses. Objective: 1) Determine the capacity of healthy SI; 2) measure ion concentrations in normal SI fluid, GR, or fluid from SI undergoing resection. The authors hypothesized that Na and Cl concentrations would be lower and higher, respectively, in GR as compared to SI fluid from healthy horses, while there would be little difference in K concentration. Methods: Observational study: two to 15 meters of SI from 15 horses were distended with wa...
Aarts RM, Siegers EW, Serra Braganca FM, van Weeren PR.The need for comprehensive equine welfare assessments has become particularly evident amid ongoing debates about the social licence to operate in equestrian sports. During exercise, multiple physiological systems, principally the cardiovascular, respiratory, muscular, thermoregulatory, endocrine, and locomotory systems, undergo complex adaptations. To monitor and determine equine welfare, an approach that focuses on the quantitative monitoring of both physiological and psychological parameters to determine and understand the impact of equestrian sports on horses is essential. Existing and emer...
Čebulj-Kadunc N, Frangež R, Kruljc P.The aim of the study was to determine the fluctuations of selected physiological parameters in young Lipizzan stallions ( = 10) during the initial phase of their training as indicators of adaptation to a graded exercise load and stress exposure. For this purpose, four exercise tests (ExT) with lunging were carried out over a period of one year. Physiological parameters (gait speed, heart and respiratory rate (HR and RR), rectal and body surface temperature (RT and BST), and cortisol and lactate concentration (CORT and LAC)) were measured before and after training. In all ExT, gait speeds incre...
Gomes ÉR, Felix LA, Gonzaga LWF, da Silva NFD, Soares BCF, de Almeida JVFC, Souza GP, Pereira RN, Taffarel MO, Ferrante M.The combination of detomidine and midazolam may provide safer sedation with muscle-relaxant effects, which are particularly necessary during standing procedures. Unassigned: Thus, the objective of this study was to evaluate the sedative and muscle-relaxant effects of the detomidine/midazolam combination in horses through a pharmacodynamic study. Unassigned: Five horses were used and subjected to four experimental protocols: 15 µg/kg of detomidine (D15); a combination of detomidine (15 µg/kg) with 25 µg/kg (DM25), 50 µg/kg (DM50), or 75 µg/kg (DM75) of midazolam administered intravenously....
