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.
Waller CC, McLeod MD.In recent years, the potential for anabolic steroid abuse in equine sports has increased due to the growing availability of designer steroids. These compounds are readily accessible online in 'dietary' or 'nutritional' supplements and contain steroidal compounds which have never been tested or approved as veterinary agents. They typically have unusual structures or substitution and as a result may pass undetected through current anti-doping screening protocols, making them a significant concern for the integrity of the industry. Despite considerable focus in human sports, until recently there ...
Johnson CB, Bloomfield M, Taylor PM.To characterise the effects of thiopentone on the equine electroencephalogram during halothane anaesthesia. Methods: Prospective controlled study. Methods: Eight healthy Welsh mountain pony geldings between 5 and 9 years old and weighing between 270 and 330 kg (mean 301 kg). Methods: Anaesthesia was induced with thiopentone and maintained using halothane in oxygen. End tidal halothane was maintained above 0.75 and below 0.85%. EEG was recorded continuously and a binaural broad band click stimulus was provided throughout the experiment at 6.1224 Hz. An infusion of 500 mg thiopentone was given o...
Giraldo CE, Álvarez ME, Carmona JU.To compare five activation methods in equine platelet-rich plasma (PRP) by determination of platelet-derived growth factor BB (PDGF-BB) and transforming growth factor beta 1 (TGF-β1) concentrations in platelet-rich gel (PRG) supernatants. Methods: Platelet-rich plasma from 20 horses was activated by calcium chloride (CC), calcium gluconate (CG), bovine thrombin (BT), and their combinations, BTCC and BTCG. Both growth factor concentrations in PRG supernatants were measured by ELISA and compared with plasma and platelet lysates (PL) over time. Results: Growth factor concentrations were signific...
Lee YL, Clarke KW, Alibhai HI, Song DY.To evaluate the effect of ephedrine on intramuscular blood flow and hemodynamic parameters during equine anesthesia. Methods: Prospective experimental study. Methods: Six healthy adult Welsh Mountain ponies (five males, one female, mean weight: 267 kg, range: 213-347 kg). Methods: Halothane-anesthetized ponies received an IV bolus of ephedrine (0.1 mg kg), followed 30 minutes later by a second IV ephedrine injection (0.2 mg kg). Changes in intramuscular blood flows (IMBF) in upper and lower triceps brachii were measured by laser Doppler flowmetry. Cardiopulmonary measurements were made at inte...
Taylor PM, Luna S, Dye A.To determine the effects of surgery, hypoxia, hypercapnia and flunixin administration on plasma β-endorphin immunoreactivity (BEI) in anaesthetized horses. Methods: Prospective crossover study. Methods: Six healthy adult Welsh Mountain ponies and seven healthy adult Thoroughbreds. Methods: Ponies were anaesthetized with thiopentone and halothane or with pentobarbitone and the horses with guaiphenesin, thiopentone and halothane. Ponies were anaesthetized for 2 hours and on separate occasions underwent a period of hypoxia, hypercapnia, anaesthesia only, or were given flunixin at induction. The ...
Ericsson AC, Johnson PJ, Lopes MA, Perry SC, Lanter HR.Horses are exquisitely sensitive to non-specific gastrointestinal disturbances as well as systemic and extraintestinal conditions related to gut health, yet minimal data are available regarding the composition of the microbiota present in the equine stomach, small intestine, and cecum and their relation to fecal microbiota. Moreover, there is minimal information regarding the concordance of the luminal and mucosal microbial communities throughout the equine gut. Illumina-based 16S rRNA gene amplicon sequencing of the luminal and mucosal microbiota present in seven regions of the gastrointestin...
Duke T, Cruz AM, Cruz JI, Howden KJ.To compare the cardiopulmonary effects of the head-down position, with or without capnoperitoneum, in halothane-anesthetized horses. Methods: Prospective randomized study. Methods: Five ponies (four mares, one stallion; bodyweight 302 ± 38.4 kg [mean ± SD]) were used. Methods: The ponies were anesthetized with xylazine, guiafenesin, ketamine, and maintained with halothane/oxygen and lungs were ventilated to 40 ± 2 mm Hg (5.3 ± 0.3 kPa) end-tidal CO tension. After baseline cardiopulmonary measurements, ponies were kept in horizontal position for 30 minutes, then tilted head-down 30° to the...
Van Dijk P, Lankveld D, Rijkenhuizen A, Jonker FH.To assess the hormonal, metabolic and physiological effects of laparascopic surgery performed under a sedative analgesic combination of detomidine and buprenorphine in standing horses. Methods: Prospective study. Methods: Eight healthy adult Dutch Warmblood horses and five healthy adult ponies undergoing laparoscopy were studied. Five healthy adult horses not undergoing laparoscopy were used as a control group. Methods: The sedative effect of an initial detomidine and buprenorphine injection was maintained using a continuous infusion of detomidine alone. The heart and respiratory rate, arteria...
Roger T, Ruckebusch Y.The motor responses of the caecum and colon to stimulation of alpha 2-adrenoceptors by xylazine and detomidine at the recommended dose levels of 0.6 and 0.1 mg/kg were investigated in three ponies. The motor changes of the left ventral colon induced by continuous intra-arterial infusion of a prostaglandin (PGF2 alpha) were used to assess the relative inhibitory effects of xylazine and detomidine in a colic model. The administration of alpha 2-agonists inhibited the spiking activity on the whole of the large intestine for 20-30 min (xylazine) or 2-3 h (detomidine). However, the detomidine-induc...
Sayasith K, Lussier J, Doré M, Sirois J.Little is known about the expression and regulation of epiregulin (EREG) and amphiregulin (AREG) in ovarian follicles of large monoovulatory animal species. To characterize the gonadotropin-dependent regulation of EREG and AREG mRNAs in equine follicles prior to ovulation, extracts were prepared from equine follicles collected during estrus between 0 and 39h post-hCG and corpora lutea obtained on day 8 of the estrous cycle (day 0=day of ovulation). Results from RT-PCR/Southern blot analyses showed that levels of EREG and AREG mRNAs were very low in follicles obtained at 0h but increased therea...
Bourzac CA, Koenig JB, Link KA, Nykamp SG, Koch TG.To evaluate the efficacy and effects of labeling equine umbilical cord blood (UCB)- and bone marrow (BM)-derived multipotent mesenchymal stromal cells (MSCs) with an ultrasmall superparamagnetic iron oxide (SPIO) contrast agent and the detection of labeled MSCs by use of MRI. Methods: UCB MSCs from placental tissues of 5 foals and BM MSCs from 5 horses. Methods: UCB and BM MSC cultures were seeded in duplicate (5,000 cells/cm(2)). One duplicate was incubated with SPIO (50 μg/mL); the other was processed identically, but without SPIO. Mesenchymal stromal cells were expanded in triplicates for ...
Freytag C, Seeger J, Siegemund T, Grosche J, Grosche A, Freeman DE, Schusser GF, Härtig W.The present study was performed on whole-mount preparations to investigate the chemical neuroanatomy of the equine myenteric plexus throughout its distribution in the intestinal wall. The objective was to quantify neurons of the myenteric plexus, especially the predominant cholinergic and nitrergic subpopulations. Furthermore, we investigated the distribution of vasoactive intestinal polypeptide and the calcium-binding protein calretinin. Samples from different defined areas of the small intestine and the flexura pelvina were taken from 15 adult horses. After fixation and preparation of the ti...
White SH, Wohlgemuth S, Li C, Warren LK.Exercise is known to promote mitochondrial biogenesis in skeletal muscle as well as enhance mitochondrial function and efficiency in human and rodent models. These adaptations help to decrease exercise-associated production of reactive oxygen species, which can negatively affect health and performance if antioxidant mechanisms are overwhelmed. Little is known about the adaptations of mitochondria in response to exercise training in the growing horse or if supplementation with a dietary antioxidant can improve mitochondrial function. To evaluate the separate and combined effects of selenium (Se...
Timoney JF, Suther P, Velineni S, Artiushin SC.Resistance to phagocytosis is a crucial virulence property of Streptococcus equi (Streptococcus equi subsp. equi; Se), the cause of equine strangles. The contribution and interdependence of capsule and SeM to killing in equine blood and neutrophils were investigated in naturally occurring strains of Se. Strains CF32, SF463 were capsule and SeM positive, strains Lex90, Lex93 were capsule negative and SeM positive and strains Se19, Se1-8 were capsule positive and SeM deficient. Phagocytosis and killing of Se19, Se1-8, Lex90 and Lex93 in equine blood and by neutrophils suspended in serum were sig...
Janczarek I, Wiśniewska A, Tkaczyk E, Wnuk-Pawlak E, Kaczmarek B, Liss-Szczepanek M, Kędzierski W.Cooling a horse after intensive exercise under hot conditions is commonly recommended. The study aimed to analyze changes in the rectal and surface temperature of the horses subjected to various water cooling treatments. This followed medium-intensity exercise performed by leisure horses under moderate air temperature. The experiment involved a control group without water application, and three variants of water cooling applied to 19 warmblood geldings after medium-intensity effort. Cooling of lower, upper, and lower and upper body parts was performed. In each variant, the rectal and body surf...
Serteyn D, Sandersen C, Lejeune JP, de la Rebière de Pouyade G, Ceusters J, Mouithys-Mickalad A, Niesten A, Fraipont A, van Erck E, Goachet AG....Intense physical exercise can induce the degranulation of neutrophils leading to an increase in plasma concentration of the neutrophil marker enzymes myeloperoxidase (MPO) and elastase (ELT). These enzymes have pro-oxidative and pro-inflammatory properties and may play a role in the exercised-induced muscular damage. Objective: To measure MPO and ELT concentrations in plasma and muscles of endurance horses and to correlate them to the extent of exercise-induced muscular damage. Methods: Seven endurance horses qualified on 120 km races were tested in this study. Neutrophil count, serum creatine...
Pollin MM, Griffiths IR.Primary dysautonomias appear to be the result of initial damage to the protein synthetic pathway of a specific neuronal population, but despite detailed morphological study of several species there is, as yet, no indication of the precise lesion or the nature of the causal agent. The very marked similarities between the species with regard to lesion type, distribution, the age group affected and the geographical restrictions of occurrence would suggest a very similar, if not common, aetiology. There is no explanation, however, for the 70 year gap between its appearance in horses and its subseq...
Katepalli MP, Adams AA, Lear TL, Horohov DW.Telomeres, specialized structures present at the ends of linear eukaryotic chromosomes, function to maintain chromosome stability and integrity. Telomeres shorten with each cell division eventually leading to replicative senescence, a process thought to be associated with age-related decline in immune function. We hypothesized that shortened PBMC telomere length is a factor contributing to immunosenescence of the aged horse. Telomere length was assessed in 19 horses ranging in age from 1 to 25 years. Mitogen-induced 3H-thymidine incorporation, total serum IgG, and pro-inflammatory cytokine exp...
Clegg PD, Burke RM, Coughlan AR, Riggs CM, Carter SD.The cellular production by resident articular cells and infiltrating inflammatory cells of the gelatinase matrix metalloproteinases (MMP) was investigated by tissue culture methods and analysis of cell supernatants by gelatin zymography. Peripheral blood neutrophils in short term culture produced MMP-9, as did peripheral blood monocytes in culture. Isolated articular chondrocytes in monolayer culture produced both MMP-2 and MMP-9, although articular cartilage maintained as explant culture produced MMP-2 alone. Synovial fibroblasts grown in monolayer culture produced MMP-2 alone, although synov...
Reef VB.Physiological flow murmurs occur frequently in horses and may be difficult to distinguish from murmurs associated with underlying cardiac disease. The significance of heart murmurs auscultated in horses is often difficult to determine if the horse is not exhibiting any clinical signs or if the signs, such as poor performance, are nonspecific. A complete echocardiographic examination (M-mode, 2-dimensional (2-D) and Doppler) provides an objective assessment of the severity of the horse's underlying cardiac disease. Valvular regurgitation and ventricular septal defects (VSDs) occur frequently an...
How MJ, Gonzales D, Irwin A, Caro T.Of all hypotheses advanced for why zebras have stripes, avoidance of biting fly attack receives by far the most support, yet the mechanisms by which stripes thwart landings are not yet understood. A logical and popular hypothesis is that stripes interfere with optic flow patterns needed by flying insects to execute controlled landings. This could occur through disrupting the radial symmetry of optic flow via the aperture effect (i.e. generation of false motion cues by straight edges), or through spatio-temporal aliasing (i.e. misregistration of repeated features) of evenly spaced stripes. By r...
McClure SR, VanSickle D, Evans R, Reinertson EL, Moran L.Extracorporeal shock-wave therapy (ESWT) may stimulate healing of desmitis in multiple species. The objective of this study was to evaluate the ultrasonographic and histologic appearance of collagenase-induced suspensory ligament (SUL) desmitis in untreated ligaments and ligaments treated with ESWT in horses. Four mature horses had SUL desmitis induced in both forelimbs. Beginning 3 weeks after induction of the lesions, one ligament per horse was treated 3 times at 3-week intervals with ESWT. The percent lesion, echogenicity and fiber alignment scores of the SULs were evaluated at 3-week inter...
Rendle DI, Litchfield E, Gough S, Cowling A, Hughes KJ.Previous reports suggest that adrenocorticotrophic hormone (ACTH) degrades rapidly, limiting its use as a diagnostic test. Objective: This study quantified effects of processing delays on ACTH concentrations and investigated the addition of N-phenylmaleimide (maleimide), a protease inhibitor, as a means of reducing ACTH degradation. Methods: Experimental study. Methods: Venous blood was collected from 8 healthy horses and 8 horses with pituitary pars intermedia dysfunction (PPID) with a range of ACTH concentrations. Baseline ACTH concentrations were established immediately using a chemilumines...
Anderson JR.Although some definitions of thanatology-broadly definable as the study of death and dying-exclude nonhumans as subjects, recognition of the scientific value of studying how other species respond to sick, injured, dying and dead conspecifics appears to be growing. And whereas earlier literature was largely characterized by anecdotal descriptions and sometimes fanciful interpretations, we now see more rigorous and often quantitative analysis of various behaviors displayed towards conspecifics (and sometimes heterospecifics) at various stages of incapacitation, including death. Studies of social...
Hanggi EB, Ingersoll JF.This study investigated lateral vision in horses (Equus caballus) for the first time from a behavioral point of view. Three horses were tested using a novel experimental design to determine the range of their lateral and caudolateral vision with respect to stimulus detection and discrimination. Real-life stimuli were presented along a curvilinear wall in one of four different positions (A, B, C, D) and one of two height locations (Top, Bottom) on both sides of the horse. To test for stimulus detection, the correct stimulus was paired against a control; for stimulus discrimination, the correct ...
Alberghina D, Giannetto C, Piccione G.The purpose of this study was to evaluate the influence of exercise on plasma tryptophan (TRP) and free serotonin (f5-HT), whole blood-5-HT (WB-5-HT) and f5-HT/WB-5-HT ratio in Italian Saddle horses. Six clinically healthy Italian Saddle horses were subjected to a 450 meters obstacles course. Blood samples were collected from each horse by jugular venipuncture using vacutainer tubes with K(3)-EDTA at rest, immediately after exercise, and after 30 min. TRP, f5-HT and WB-5-HT were analyzed by HPLC. Immediately after exercise, statistically significant increases of f5-HT (p <0.001) and WB-5-HT (p...
Vail TB, Trotter GW, Powers BE.The osteoinductive capability of four particle sizes of equine demineralized bone matrix (DBM) was evaluated. Matrix particles were implanted in brachiocephalicus muscle pouches in six horses and were harvested 8 weeks later. Matrix particle sizes of 2.0 mm3 to 4.0 mm3 and 5.0 mm3 to 10.0 mm3 were associated with osteoinductive activity and minimal signs of local inflammation. The two smaller particle sizes (0.425 mm3 to 0.850 mm3 and 0.850 mm3 to 2.0 mm3) were minimally osteoinductive and were associated with a greater local inflammatory response. Microscopic events associated with new bone p...
Thomasy SM, Steffey EP, Mama KR, Solano A, Stanley SD.Fentanyl decreases the minimum alveolar concentration (MAC) of inhaled anaesthetics and has been used clinically to reduce the requirements of other anaesthetic drugs in humans and small animals. We hypothesized that i.v. fentanyl would decrease the MAC of isoflurane in horses in a dose-dependent manner. Methods: Following determination of baseline MAC of isoflurane, fentanyl was administered i.v. to target plasma concentrations of 1, 8 and 16 ng ml(-1). Each horse was randomly assigned two of three target concentrations administered in ascending order. Loading and infusion doses for each hors...
Phillips JC, Lembcke LM, Noltenius CE, Newman SJ, Blackford JT, Grosenbaugh DA, Leard AT.To determine the tissue-restricted expression pattern of tyrosinase mRNA in canine and equine melanocytic tumors and relative tyrosinase and major histocompatibility complex (MHC) I mRNA expression in variants of melanocytic tumors. Methods: 39 canine and 8 equine tumor samples and 10 canine and 6 equine normal tissue samples. Methods: RNA was isolated from formalin-fixed, paraffin-embedded tissues. Real-time PCR assays were designed to amplify canine and equine tyrosinase, S18 ribosomal RNA, and major histocompatibility complex I transcripts. Relative expression was determined by use of S18 a...
Betteridge KJ.Carl Hartman's title of 47 years ago is invoked in tribute to his first recovery of a bovine embryo 30 years before that, and his legacy of an emphasis on the value of descriptive and comparative studies in reproductive biology. The horse's qualification as a farm animal has waned since those times but, in a conference understandably dominated by research in ruminants and pigs, there are lessons to be learned from some peculiarities of equine embryonic development. Morphological and physiological features of the conceptus and its interaction with its environment during the first month of pregn...
Lanata A, Guidi A, Valenza G, Baragli P, Scilingo EP.We present a study focused on a quantitative estimation of a human-horse dynamic interaction. A set of measures based on magnitude and phase coupling between heartbeat dynamics of both humans and horses in three different conditions is reported: no interaction, visual/olfactory interaction and grooming. Specifically, Magnitude Squared Coherence (MSC), Mean Phase Coherence (MPC) and Dynamic Time Warping (DTW) have been used as estimators of the amount of coupling between human and horse through the analysis of their heart rate variability (HRV) time series in a group of eleven human subjects, a...
Dallap Schaer BL, Epstein K.To review the hemostasis literature relevant to development of coagulopathy in the critically ill equine patient. Methods: Original scientific and review articles. Results: Inflammation plays a critical role in the activation and amplification of clot formation, as well as the impairment of physiologic anticoagulant mechanisms, and fibrinolysis. Earlier identification of coagulopathy in patients at risk and restoration of physiologic hemostasis may result in better outcome. Development of scoring systems based on information other than coagulation markers alone may better identify patients wit...
Hasan M, Siegmund W, Oswald S.Cytochrome P450 3A (CYP) enzymes are involved in the elimination of many drugs and are known to be regulated by several environmental factors. Thus, it was the aim of this study to develop and validate an analytical method allowing estimation of the hepatic CYP3A enzyme activity using the 4-hydroxycholesterol to cholesterol ratio as an endogenous biomarker in serum. Both compounds were isolated from the biological matrix by liquid-liquid extraction using n-hexane after saponification with ethanolic sodium methoxide solution (2M) to cleave the steroids from their esterified forms without any ki...
Marsbøll AF, Christensen JW.Inclusion of objective temperament tests at practical horse breeding evaluations is of increased interest. It has been debated whether such tests may involve human handling, since there may be considerable differences in horses' handling experience. Objective: To investigate the effect of a short-term standardised handling procedure on reactions of young horses in 2 types of fear tests (including and excluding human handling). Methods: An experimental study with 3-year-old Icelandic horses (n = 24). Methods: Handled horses (n = 12) were trained according to a standardised handling procedure wh...
Keller LE, Tait Wojno ED, Begum L, Fortier LA.To gain insight into Treg interactions with synovial tissues in early OA, an equine tri-culture model of OA was used to test the hypothesis that Tregs, in the absence of T Helper 17 cells, are sufficient to resolve inflammation elicited by IL-1β. Unassigned: To model normal and OA joints, synoviocytes were co-cultured with chondrocytes in a transwell system and ± stimulated with IL-1β. Tregs were activated and enriched, then added to co-cultures, creating tri-cultures. At culture end, synoviocytes and chondrocytes were analyzed for gene expression, Treg Foxp3 expression was reexamined b...
McCarty CA, Thomason JJ, Gordon KD, Burkhart TA, Milner JS, Holdsworth DW.To assess whether the transient stresses of foot impact with the ground are similar to those found during midstance loading and if the location of high stress correlate with the sites most commonly associated with mechanically induced osteoarthritis (OA). We compared impact stresses in subchondral bone between two subject-specific, three-dimensional, finite-element models of the equine metacarpophalangeal (MCP) joint-one with advanced OA and one healthy, and with similar published data on the stresses that occur at midstance. Methods: Two right MCP joints (third metacarpal and proximal phalanx...
Gibson JS, Godart H, Ellory JC, Staines H, Honess NA, Cossins AR.Potassium transport was measured in equine red blood cells, using 86Rb+ influx as a convenient assay. A significant component of volume- and pH-sensitive K(+)-Cl- cotransport to the overall K+ flux was observed in all blood samples studied, although fluxes were variable between animals, and within individuals when measured at intervals over a period of weeks. The aryloxyacetic acid [(dihydroindenyl)oxy]alkanoic acid (DIOA), at a final concentration of 100 microM, inhibited most (> 95%) of the Cl(-)-dependent K+ flux, and DIOA sensitivity was therefore used to define the activity of the K(+)...
McTaggart C, Yovich JV, Penhale J, Raidal SL.Flow cytometric assays were used to compare phagocytic and oxidative burst activity of neutrophils from healthy foals less than 7 days of age with the activity of cells from healthy adult horses. The phagocytosis of Staphylococcus aureus by foal neutrophils was less than that observed for adult neutrophils when autologous serum was used as the source of opsonins in the assay. The use of adult serum did not significantly improve the ability of foal neutrophils to attach bacteria. The oxidative burst activity of foal neutrophils was equivalent to that of adult cells. However, when serum or plasm...
