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Topic:Physiology
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.
Coordinated changes of kinematics and muscle fibre properties with prolonged endurance training. The objective of this study was to investigate the relationship between kinematic variables and muscle characteristics by determining (1) if heavy endurance training alters these variables and (2) if such modifications occur in a coordinated manner. Fifteen Andalusian stallions age 41-45 months were used. Five horses were used as controls and 10 horses underwent a training programme based on aerobic exercise for 8 months. Intensity of exercise was adjusted individually for each horse according to a standardised exercise test. Stride kinematic characteristics at the trot were analysed by videog...
Effects of heel and toe elevation upon the digital joint angles in the standing horse. Five sound mature horses, age 8-14 years, with toe angles 45.5-55.0 degrees were placed on a specially designed platform with only the left forelimb weightbearing, which allowed the successive production of 7 different conditions of foot orientation: neutral position (N), 5, 10, 15 degrees heel (H5, H10, H15) and toe (T5, T10, T15) elevation, performed according to 2 different sequences. For each condition, 2 lateromedial radiographs were taken to evaluate the metacarpophalangeal joint (MPJ) and both interphalangeal joint (PIPJ and DIPJ) angles, respectively. In addition, two-dimensional (2-D)...
Three-dimensional kinematics of the equine spine during canter. Most research on equine kinematics has previously been performed in the walking and/or trotting animal. This is also true for the few studies on the kinematics of the equine back. These studies have, for the major part, focused on the flexion-extension movement in the sagittal plane. However, vertebrae can rotate in 3 dimensions. This study was designed to determine all 3 rotations in various segments of the vertebral column of a cantering horse. Five Dutch Warmblood horses were measured during treadmill canter (7.3 m/s). Steinmann pins were inserted into the dorsal spinous processes of 8 thor...
Effects of treadmill speed on the mechanics of the back in the trotting saddlehorse. Speed related changes in trunk mechanics have not yet been investigated, although high-speed training is currently used in the horse. To evaluate the effects of speed on back kinematics and trunk muscles activity, 4 saddle horses were recorded while trotting on a horizontal treadmill at speeds ranging from 3.5 to 6 m/s. The 3-dimensional (3-D) trajectories of skin markers on the left side of the horse and the dorsal midline of the trunk were established. Electrical activity was simultaneously obtained from the longissimus dorsi (LD) and rectus abdominis (RA) muscles using surface electrodes. T...
Relationships between third metacarpal bone parameters and surface strains. The relationships were explored between measurements of bone quality, size (quantity) and shape, and strain data collected during treadmill exercise at 4 and 12 m/s from the third metacarpal bones of 6 yearling and 6 mature Thoroughbred racehorses. Peak strains in yearling and mature Thoroughbred horses during exercise were related to the size and shape of the third metacarpal bone. The peak strains were significantly lower in horses with a greater cross-sectional area of bone and with a greater proportion of the bone in the dorsal cortex. There was no consistent relationship between peak stra...
Distribution of epidermal growth factor receptor (EGFr) in normal and acute peptic-injured equine gastric squamous epithelium. Growth factors are important in healing and restoration of injured gastrointestinal tissues and, therefore, we characterised temporally the distribution and density of epidermal growth factor receptor (EGFr) in normal and peptic-injured gastric squamous epithelium of horses. Lesions were induced in the equine gastric squamous epithelium using a feed deprivation protocol that results in prolonged increased gastric acidity. Fifteen mature horses, 9 geldings and 6 mares, age 3 to 20 years, were used and divided into 3 groups: Group 1 (n = 5) were subjected to euthanasia for problems unrelated to ...
Effects of an external nasal strip and frusemide on pulmonary haemorrhage in Thoroughbreds following high-intensity exercise. The purpose of this study was to examine the effects of an external nasal strip (NS), frusemide (FR) and a combination of the 2 treatments (NS + FR) on exercise-induced pulmonary haemorrhage (EIPH) in Thoroughbred horses. It was hypothesised that both the NS and FR would attenuate EIPH as assessed by red blood cell count in bronchoalveolar lavage fluid. In random order, 8 horses completed each of 4 sprint exercise tests on a treadmill: 1) NS; 2) FR (0.5 mg/kg bwt i.v., 4 h pre-exercise); 3) NS + FR; and 4) control (C; no treatment). After a 5 min warm-up (4.5 m/s), horses completed 2 min runni...
Effect of romifidine on gastrointestinal motility, assessed by transrectal ultrasonography. A technique of transrectal ultrasonography was developed to investigate the effects of romifidine 80 and 120 microg/kg bwt on intestinal motility in the horse. Motility of the small intestine, caecum and left ventral colon were assessed following injection of romifidine and a saline control, using a blinded, cross-over study design in 6 horses. Measurements were taken at 15, 30, 60, 120, 180 and 240 min after drug administration. There was a slight nonsignificant decrease in motility in the control group over the 4 h study period. Both doses of romifidine produced a marked decrease in gastroin...
Factors influencing blood flow in the equine digit and their effect on uptake of 99m technetium methylene diphosphonate into bone. It was hypothesised that exercise may promote perfusion of the distal part of the limbs and enhance uptake of radiopharmaceutical into bone, but bandaging and lameness would have no effect. Two hundred and two horses undergoing routine nuclear scintigraphic examination for assessment of lameness or poor performance between November 1998 and November 1999 were assigned randomly to one of 4 groups: no bandages and no exercise (NB/NE); bandages and no exercise (B/NE); no bandages and exercise (NB/E); bandages and exercise (B/E). In the bandage groups, the distal forelimbs were bandaged for at lea...
Application of a constant blood withdrawal method in equine exercise physiology studies. The aim of the present study was to test a constant blood withdrawal method (CBWM) to collect blood samples from horses during treadmill exercise. CBWM was performed in 4 Standardbreds and 5 Haflinger horses. A peristaltic pump was used to control blood aspiration from an i.v. catheter via an extension line. Blood was collected using an automatic fractions collector, with a constant delay time between the drawing of blood and sample collection. Blood withdrawal using CBWM was made during a treadmill standardised exercise test (SET). A blood flow of 12 m/min was used and samples collected every...
Quantification of the response of equine apocrine sweat glands to beta2-adrenergic stimulation. The aim of the present study was to characterise the quantitative sweating response of the horse to beta2-adrenergic stimulation. The sweating responses of 6 horses to the randomised infusion of 8 different adrenaline concentrations (0.025, 0.05, 0.075, 0.1, 0.2, 0.4, 1.0 or 2.0 microg/kg bwt/min), was investigated. Sweating rate (SR) and skin temperature (TSK) on the neck (N) and gluteal region (G), and plasma adrenaline and noradrenaline concentrations were measured. Peak SR was approximately 15 (N) and approximately 9 g/m2/min (G) during infusion of both 1.0 and 2.0 microg/kg bwt/min adrena...
Flowmetric comparison of respiratory inductance plethysmography and pneumotachography in horses. Respiratory inductance plethysmographic (RIP) and pneumotachographic (Pn) flows were compared dynamically in horses with bronchoconstriction. On a breath-by-breath basis, RIP was normalized to inspiratory volume from Pn, and peak [peak of subtracted final exhalation waveform (SFE(max))] and selected area [integral of subtracted final waveform during first 25% of exhaled volume (SFE(int))] differences between RIP and Pn flows during early expiration were measured in three settings: 1) healthy horses (n = 8) undergoing histamine bronchoprovocation; 2) horses with naturally occurring lower airway...
NO inhalation reduces pulmonary arterial pressure but not hemorrhage in maximally exercising horses. In horses, the exercise-induced elevation of pulmonary arterial pressure (Ppa) is thought to play a deterministic role in exercise-induced pulmonary hemorrhage (EIPH), and thus treatment designed to lower Ppa might reasonably be expected to reduce EIPH. Five Thoroughbred horses were run on a treadmill to volitional fatigue (incremental step test) under nitric oxide (NO; inhaled 80 ppm) and control (N(2), same flow rate as per NO run) conditions (2 wk between trials; order randomized) to test the hypothesis that NO inhalation would reduce maximal Ppa but that this reduction may not necessarily ...
Extravascular lung water in the exercising horse. Seven Standardbred horses were exercised on a treadmill at speeds (approximately 12 m/s) producing maximal heart rate, hypoxemia, and a mean pulmonary arterial pressure of approximately 75 mmHg. Extravascular lung water was measured by using transients in temperature and electrical impedance of the blood caused by a bolus injection of cold saline solution. Lung water was approximately 3 ml/kg body wt when standing but did not increase significantly with exertion. We conclude that any increase in fluid extravasation from the pulmonary hypertension accumulates in the lung at a level that is less...
Pregnancy-associated plasma protein-A (PAPP-A) in ovine, bovine, porcine, and equine ovarian follicles: involvement in IGF binding protein-4 proteolytic degradation and mRNA expression during follicular development. IGF binding protein-4 (IGFBP-4) proteolytic degradation is a common feature of preovulatory follicles from human, ovine, bovine, porcine, and equine ovary. In all these species, the protease is a zinc-dependent metalloprotease and its ability to degrade IGFBP-4 is IGF dependent. The human intrafollicular IGFBP-4-degrading protease has recently been identified as pregnancy-associated plasma protein-A (PAPP-A). The aim of this study was to investigate whether PAPP-A is also involved in IGFBP-4 degradation in ovine, bovine, porcine, and equine preovulatory follicles and to study the expression of...
In vitro evaluation of a customized solution for use in attenuating effects of ischemia and reperfusion in the equine small intestine. To determine whether a customized solution could attenuate the effects of low-flow ischemia and reperfusion injury of the equine jejunum. Methods: A segment of jejunum obtained from 21 healthy adult horses. Methods: A segment of jejunum was maintained in an isolated extracorporeal circuit, and arterial flow was reduced to 20% of baseline for 40 minutes (ischemia) followed by 60 minutes of reperfusion. In 1 group, a customized solution was infused at a rate of 1 ml/min during low-flow ischemia and 3 ml/min during reperfusion. In a second group, the solution was infused at the same rate during l...
Effects of superior check desmotomy on flexor tendon and suspensory ligament strain in equine cadaver limbs. To measure the effects of transection of the accessory ligament of the superficial digital flexor (SDF) muscle (superior check desmotomy) on flexor tendon and suspensory ligament (SL) strain in vitro. Methods: In vitro experimental biomechanical investigation. ANIMALS USED: Ten equine cadaver forelimbs. Methods: The effects of superior check desmotomy were determined using equine cadaver forelimbs secured in a servocontrolled hydraulic testing machine. Strain sensors were used to measure strain on the superficial and deep digital flexor tendons and SL, and a goniometer was used to measure join...
Evaluation of a signal-adapted filter for processing of periodic electromyography signals in horses walking on a treadmill. To evaluate an adaptive-filter method for use in analysis of periodic electromyography (EMG) signals in which the transfer function of the filter is matched to characteristics of the signal. Methods: 15 adult horses without clinical signs of back pain. Methods: Electromyography signals of the left and right longissimus dorsi muscles, middle gluteal muscles, and triceps brachii muscle were recorded from horses walking on a treadmill, using bilaterally placed surface electrodes. A reflective marker was placed on the hoof of the left hind limb for simultaneous kinematic measurement of motion cycl...
Effect of topical anesthesia of the laryngeal mucosa on upper airway mechanics in exercising horses. To determine the effect of desensitization of the laryngeal mucosal mechanoreceptors on upper airway mechanics in exercising horses. Methods: 6 Standardbreds. Methods: In study 1, videoendoscopic examinations were performed while horses ran on a treadmill with and without topical anesthesia of the laryngeal mucosa. In study 2, peak tracheal and nasopharyngeal pressures and airflows were obtained from horses during incremental treadmill exercise tests, with and without topical anesthesia of the laryngeal mucosa. A nasal occlusion test was performed on each horse while standing during an endosco...
Co-ordinated expression of contractile and non-contractile features of control equine muscle fibre types characterised by immunostaining of myosin heavy chains. Combined methodologies of immunohistochemistry, histochemistry and photometric image analysis were applied: (1) to characterise control equine skeletal muscle fibres according to their myosin heavy chain (MyHC) composition and (2) to determine on a fibre-to-fibre basis the correlation between contractile [i.e. MyHC(s), myofibrillar ATPase (mATPase) and sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) isoforms], metabolic [i.e. succinate dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (GPD) activities, glycogen and phospholamban (PLB) contents], and morphological [i.e. cross-sect...
Osmotic tolerance of equine spermatozoa and the effects of soluble cryoprotectants on equine sperm motility, viability, and mitochondrial membrane potential. Osmotic stress attributed to differences in the relative permeability of cryoprotectants, such as glycerol and water, appears to be an important factor in cryodamage. The objective of this study was to characterize the osmotic tolerance of equine spermatozoa, and to evaluate the effects of addition and removal of cryoprotectants from equine spermatozoa on their motility, and membrane and acrosomal integrity, as well as their mitochondrial membrane potential. Equine spermatozoa had a limited osmotic tolerance to anisosmotic conditions. Although the addition of increasing concentrations of glyce...
The isolation and identification of steroidal sapogenins in switchgrass. Switchgrass (Panicum virgatum L.) has been reported to be hepatotoxic, causing photosensitization in lambs and horses. In this study we show the presence of steroidal saponins in two samples of switchgrass that has been implicated in the poisonings of sheep and horses. After hydrolysis of the saponins, diosgenin was determined to be the major sapogenin in both switchgrass samples. We also confirmed the presence of diosgenin in kleingrass after hydrolysis of saponins extracted from it.
In vivo imaging of physiological angiogenesis from immature to preovulatory ovarian follicles. To develop a model for the study of physiological angiogenesis, we transplanted ovarian follicles onto striated muscle tissue and analyzed the process of microvascularization in vivo using repeated fluorescence microscopy. Follicles were mechanically isolated from unstimulated as well as pregnant mare's serum gonadotropin (PMSG)- or PMSG/luteinizing hormone (LH)-stimulated Syrian golden hamster ovaries and were transplanted as free grafts into dorsal skinfold chambers of untreated or synchronized hamsters. Follicles lacking thecal cell layers did not vascularize regardless whether harvested fr...
The application of three-dimensional internal structure microscopy in the observation of mare ovary. The ovary of the mare has a unique structure which differs totally from that of other mammals. However, because of its relatively large size, conventional histological techniques were unsuitable for the observation of the internal structure of the whole ovary. Three-dimensional internal structure microscopy (3D-ISM) consists of a cryotome-CCD camera-laser disc recorder-PC-based control system coupled with a graphic workstation. The internal structure of the ovary is observed by processing over more than 1,000 stored images of serially sliced surfaces of each frozen equine ovary. The 3D reconst...
The effect of aging on T cell responses in the horse. Horses greater than 20 years of age exhibit alterations in their immune responses similar to those observed in other aged individuals. The purpose of this study was to characterize immunosenescence in a population of aged ponies. The peripheral blood mononuclear cells (PBMC) from aged ponies exhibited a decreased proliferative response to various mitogens that was not overcome by the addition of interleukin 2 (IL-2) to the cultures. No difference in overall expression of the IL-2 receptor was seen between young and aged ponies, though CD8(+) cells from aged ponies exhibited increased levels of...
Insulin responsiveness of sheep, ponies, miniature pigs and camels: results of hyperinsulinemic clamps using porcine insulin. It had been suggested that marked species differences in glucose tolerance tests were due to differences in insulin resistance. To compare insulin responsiveness, euglycemic hyperinsulinemic clamps were carried out in sheep, ponies, miniature pigs and camels. Porcine insulin was infused as primed-continuous infusions for 2 h (6 mU x kg(-1) x min(-1)). The steady state glucose infusion rates in the pigs, sheep, ponies and camels were 96.0, 18.6, 7.1 and 6.1 micromol x kg(-1) x min(-1), respectively. The maximal plasma insulin concentrations during the insulin infusions were 2,700 microU x ml(-1...
Assessment of colostral transfer and systemic availability of immunoglobulin G in new-born foals using a newly developed enzyme-linked immunosorbent assay (ELISA) system. To measure the immunoglobulin G (IgG) concentration in colostrum, milk and serum samples, a sandwich enzyme-linked immunosorbent assay (ELISA) detection system was developed. The system provided high reproducibility and sensitivity for routine diagnostic purposes. The period of fluctuating serum concentrations of IgG was monitored in new-born foals and their mares for a period of 6 weeks postnatum and postpartum, respectively. All foals received colostrum from their mares. The mean IgG concentration in the precolostral mare serum was approximately 19.0 mg/ml and decreased significantly to 13.8...
Magnetic resonance imaging of the normal equine brain. The purpose of this investigation was to define the magnetic resonance (MR) imaging appearance of the brain and associated structures of the equine head. MR images were acquired in oblique dorsal (T2-weighted), sagittal (T1-weighted), and transverse planes (T2-weighted), using a magnet of 1.5 Tesla and a human body coil. Relevant anatomic structures were identified and labeled at each level. The resulting images provided excellent anatomic detail of the cranioencephalic structures. Annotated MR images from this study are intended as a reference for clinical imaging studies of the equine head, ...
