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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.
Echocardiographic measurements of cardiac dimensions and indices of cardiac function in normal adult thoroughbred horses. Cardiac dimensions and indices of cardiac function were measured in 29 clinically normal adult Thoroughbreds (TB) which performed minimal exercise using guided M-mode and two-dimensional (2-D) echocardiography, from a variety of image planes and measurement methods, and standardised imaging planes based on intracardiac anatomical landmarks. The different methods of measuring these variables were compared. The variables which were considered to be most valuable for quantitative echocardiography were measured in a further 9 horses. Comparable measurements of cardiac dimensions can be obtained fr...
Heart murmurs in horses: determining their significance with echocardiography. 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...
Physiological valvular regurgitation in clinically normal young racehorses: prevalence and two-dimensional colour flow Doppler echocardiographic characteristics. Colour flow Doppler echocardiographic examinations were performed on 15 horses; 10 Thoroughbreds and 5 Standardbreds; 9 mares, 5 geldings and 1 stallion; mean +/- s.d. 3.4 +/- 1.1 years. Cardiac murmurs were audible in 12 horses (80%), but these had characteristics consistent with functional murmurs in all horses. A standardised two-dimensional (2-D) and M-mode echocardiographic examination was unremarkable in all horses except that aortic valve prolapse was identified in 3 horses, tricuspid valve prolapse in 2 horses and mitral valve prolapse was present in one horse. Colour flow Doppler echo...
Effects of sodium bicarbonate on fluid, electrolyte and acid-base balance in racehorses. Sodium bicarbonate given by nasogastric tube has been used by some trainers as the key ingredient in a 'milkshake'. It has been suggested that such treatment given 3-5 h prior to racing may enhance a horse's racing performance by increasing the blood buffering capacity and enhancing lactate clearance from skeletal muscle, thereby delaying the onset of fatigue. Several experiments were conducted to examine the effects on fluid, electrolyte and acid-base values of 0.5 g kg-1 dose of sodium bicarbonate, were examined. The effects of fasting, the simultaneous administration of glucose (0.5 g kg-1)...
Pulsed wave Doppler echocardiography in normal horses. Reference values were established for selected Doppler derived variables from a group of 40 normal Thoroughbred and Thoroughbred cross horses. Standard two-dimensional (2-D) images used for guiding the Doppler sampling site allowed accurate alignment with flow. Tricuspid inflow velocities during rapid filling (E) and atrial contraction (A) were significantly higher when recorded from a right parasternal angled view than from a right parasternal long-axis view. In 8 horses the tricuspid inflow peak A velocity was higher than the peak E velocity. The peak acceleration of blood flow was higher (P...
In vitro maturation of equine oocytes obtained from different age groups of sexually mature mares. Oocytes were harvested from mare ovaries obtained at slaughter and were divided into 3 groups based on the age of the donor. The age groups consisted of young (2 to 7 yr), middle-aged (8 to 14 yr) and aged (>or=15 yr) mares. There were no differences between age groups in the proportions of follicles available for examination or the proportions of normal, abnormal or total oocytes collected. After 24 h of culture, the overall maturation rate to the second metaphase (MII) was 52.7%. Maturation rates for oocytes obtained from young and middle-aged mares were similar, but oocytes from aged mar...
Characterisation of beta-adrenoceptors in equine digital veins: implications of the modes of vasodilatory action of isoxsuprine. Isolated equine digital veins (EDVs) were used to study beta-adrenoceptor mediated vasodilation and to examine isoxsuprine's vasodilatory mechanism of action. When the blood vessel wall tension was raised with potassium chloride solution (KCl; 59 mmol/l), the order of vasodilator potency of beta-agonists was: isoprenaline > fenoterol > noradrenaline > dobutamine > isoxsuprine. The beta 2-selective adrenoceptor antagonist, ICI 118551 (1 nmol/l) caused a 6.74 and 6.65-fold parallel shift to the right in the dose response curves to fenoterol and noradrenaline respectively. Propranolol...
Evidence of strain-mode-related cortical adaptation in the diaphysis of the horse radius. The relative importance that certain strain features, including mode (e.g., tension vs. compression) and magnitude, have in affecting adaptive bone remodeling seen in normal skeletally mature bones remains controversial. The equine radius is used as a model because in vivo strain data show that the mid-to-proximal diaphysis receives a consistent history of predominantly cranial-caudal bending loads, in contrast to the distal diaphysis which receives relatively more torsional loading superimposed on cranial-caudal bending. Medial and lateral cortices serve as control regions because they corres...
Prophylactic efficacy of phenytoin, acetazolamide and hydrochlorothiazide in horses with hyperkalaemic periodic paralysis. Horses with hyperkalaemic periodic paralysis were challenged with an oral dose of potassium chloride, and the prophylactic efficacy of phenytoin, acetazolamide and hydrochlorothiazide was evaluated, with at least three weeks separating the trials of each drug. After the administration of potassium chloride without prophylactic medication the horses' clinical signs ranged from generalised fine muscle fasciculations to gross tremors, and weakness with occassional prolapse of the nictitating membrane; plasma potassium concentration increased significantly (P < 0.01) from 4.0 +/- 0.2 to 6.0 +/-...
A novel uterine protein that associates with the embryonic capsule in equids. An apparently unique protein produced in large quantities by the endometrium of the mare which adheres to, or is incorporated into, the acellular capsule that surrounds the equine conceptus in early pregnancy, has been characterized and partially sequenced. It has a molecular mass of approximately 18 kDa on SDS-PAGE gels and is nonglycosylated as assessed by a sensitive carbohydrate detection kit. Comparison of its first 24 amino-terminal amino acids with all entries in the databases failed to show any significant identity with any other protein sequence. Secretion of the protein appears to be...
Amino acid sequence of HSP-1, a major protein of stallion seminal plasma: effect of glycosylation on its heparin- and gelatin-binding capabilities. We report the complete amino acid sequence of HSP-1, a major protein isolated from stallion seminal plasma or acid extracts of ejaculated spermatozoa. The protein consists of 121 amino acids organized in two types of homologous repeats arranged in the pattern AA'BB'. Each of the 13-15-residue A-type repeats contains two O-linked oligosaccharide chains. The B-type repeats span 44-47 amino acids each, are not glycosylated, and have the consensus pattern of the gelatin-binding fibronectin type-II module. This domain also occurs in the major bovine seminal plasma heparin-binding proteins PDC-109 (...
The maternal leucocyte response to the endometrial cups in horses is correlated with the developmental stages of the invasive trophoblast cells. Invading trophoblasts form endometrial cups in the endometrium of the pregnant mare. In the present study we characterized the maternal leucocyte response to endometrial cups from their formation to their regression. The maternal leucocyte response was correlated with the stages of trophoblast development. (1) Aggregates of CD4+ and CD8+ cells were present between the migrating and differentiating endometrial cup trophoblasts and surrounding the forming endometrial cups. (2) Numbers of CD4+ cells within the mature endometrial cups were much reduced. At the periphery of the endometrial cups CD4...
Interleukin-1-mediated regulation of plasminogen activation in pregnant mare serum gonadotropin-primed rat granulosa cells is independent of prostaglandin production. This study examines the effects of interleukin-1 (IL-1) on plasminogen activator (PA) activity and prostaglandin (PG) E production in pregnant mare serum gonadotropin (PMSG)-primed granulosa cells and the potential involvement of PGE in the regulation of ovarian plasminogen activation. Methods: Granulosa cells were obtained from PMSG-primed rat (27-day-old) ovaries and cultured in serum-free conditions for 48 hours in the absence or presence of IL-1 beta (10 ng/mL) with and without transforming growth factor-beta 1 (10 ng/mL). Cellular PA activity was measured through the conversion of plasmin...
Activities of selected aerobic and anaerobic enzymes in the gluteus medius muscle of endurance horses with different performance records. Biopsies of the gluteus medius muscle were taken at three different depths from 36 endurance horses aged 8.42 +/- 2.85 years and of both sexes. Twenty of the horses were considered to be excellent performers on the basis of the mean speed of their three fastest records in endurance events over the previous two or three years, whereas 16 were moderate performers. The biopsy samples were analysed for the activities of the enzymes citrate synthase (an indicator of citric acid cycle activity), 3-OH-acyl-CoA-dehydrogenase (an indicator of lipid oxidation) and lactate dehydrogenase (an indicator of ...
Sr2+ can become incorporated into an agonist-sensitive, cytoplasmic Ca2+ store in a cell line derived from the equine sweat gland epithelium. We have explored the properties of a Ca(2+)-dependent cell-signalling pathway that becomes active when cultured equine sweat gland cells are stimulated with ATP. The ATP-regulated, Ca(2+)-influx pathway allowed Sr2+ to enter the cytoplasm but permitted only a minimal influx of Ba2+. Experiments in which cells were repeatedly stimulated with ATP suggested that Sr2+, but not Ba2+, could become incorporated into the agonist-sensitive, cytoplasmic Ca2+ store. Further evidence for this was provided by experiments using ionomycin, a Ca2+ ionophore which has no affinity for Sr2+.
Comparison of the workload of Dutch warmblood horses ridden normally and on a treadmill. Six Dutch warmblood horses, ridden by an experienced rider, cantered 3320 m at a speed adapted to the individual horse's anaerobic threshold, under four different conditions: 1, on a firm shell track with the speed varying from 6.5 to 9.4 m/s; 2, on a horizontal treadmill at the same speeds and for the same duration as in test 1; 3, on a horizontal treadmill for the same duration as in tests 1 and 2, but at a 10 per cent higher speed; and 4, on a treadmill at the same speed and for the same duration as in test 1, but at an inclination of 1 to 2 per cent adjusted individually to obtain heart ra...
Partial sequence of the equine immunoglobulin epsilon heavy chain cDNA. In order to isolate a part of the immunoglobulin E (IgE) heavy chain cDNA of the horse, primers have been designed based upon well conserved sequences in humans, sheep and rats. The PCR resulted in a 500 bp fragment which hybridised with a human IgE constant region probe. The fragment was cloned and sequenced and its derived protein sequence compared with the corresponding sequences in humans, sheep and mice. Most amino acids common to these three species are also shared by the horse.
Aseptic tenosynovitis of the digital flexor tendon sheath, fetlock and pastern annular ligament constriction. The anatomy of the digital flexor tendon sheath and related tendons and ligaments is described. Diagnosis and management of acute tenosynovitis and long-term tenosynovitis and associated tendon injuries are discussed, as well as the syndrome of stenosis of the fetlock canal (or fetlock annular ligament constriction) and palmar annular ligament constriction. Desmitis of the palmar annular ligament is also described.
Ligaments associated with joints. This article contains a short introduction to the anatomy, physiology, and pathophysiology of ligaments associated with diarthrodial joints. Individual ligaments are discussed on a regional basis as forelimb, distal limb, and hindlimb. Emphasis is placed on the anatomy of the ligaments because this is the key to sound clinical application of their involvement in joint disease. There are few conditions of diarthrodial joints that do not involve their associated ligaments, and this role may be in causative, diagnostic, and therapeutic or convalescent considerations.
[Heart rate fluctuations in the horse at rest: (2) Biological variation factors related to behavioural profile]. Variability of heart rate was analysed within a sample of 30 horses in order to determine the influence of factors (animal, age, sex and breed) associated with different behavioural patterns. The heart rate fluctuations were analysed by computing the power spectral density of a series of heartbeat intervals. A generalized linear model was used to compare the spectra and to reveal the effect of each factor: animal age, sex and breed. The scale and shape of spectral densities were significantly different between animals. This individual variability was partly explained by the sex and age effects...
Miscellaneous conditions of tendons, tendon sheaths, and ligaments. The use of diagnostic ultrasonography has greatly enhances our ability to diagnose injuries of tendons and tendon sheaths that were previously either unrecognized or poorly understood. For may of these injuries, there is currently only a small amount of follow-up data. This article considers injuries of the deep digital flexor tendon and its accessory ligament, the carpal tunnel syndrome soft tissue swellings on the dorsal aspect of the carpus, intertubercular (bicipital) bursitis and bicipital tendinitis, injuries of the gastrocnemius tendon, common calcaneal tendinitis, rupture of peroneus (...
Microscopic anatomy of the equine skin with special reference to the dermis. We have observed and re-evaluated the histology of the skin of the horse, using samples from four Thoroughbreds. The skin was composed of the usual three components: epidermis, dermis and subcutis. In particular, the dermis was found to have three fibrous components: a papillary layer, a reticular layer and a cordovan-leather tissue layer. The cordovan-leather tissue layer was subdivided into a superficial main layer and a deeper accessory layer. The superficial main layer was thick, and present in all of the skin samples. The deeper accessory layer was found in the dorsal and dorso-lateral pa...
Localisation of alkaline phosphatase in equine growth cartilage. The aim of this study was to localise alkaline phosphatase (ALP) activity in equine growth cartilage both histochemically and ultrastructurally. For histochemical studies, full thickness growth cartilage samples were obtained from 6 anatomical sites from 16 horses and ponies ranging in age from 90 d postconception to 12 years of age. For ultrastructural studies, samples were obtained from the lateral trochlear ridge of the distal femur of 3 animals ranging in age from 157 d postconception to 12 months of age. Alkaline phosphatase in histological sections was localised using a substituted napht...
Equine pelvic flexure myoelectric activity during fed and fasted states. The pelvic flexure is the midpoint of the equine large colon that marks the junction of dorsal and ventral components. Previous studies of intraluminal pressure in this region indicate that it could be an important motility control center. The present study was undertaken to expand our knowledge of normal myoelectric activity around the pelvic flexure region. Eight bipolar silver wire electrodes were surgically fixed at 5-cm intervals to the colonic serosa of five adult horses, starting 30 cm oral to the pelvic flexure on the left ventral colon and ending 15 cm aboral to the pelvic flexure on ...
Detection of immunoreactive atrial and brain natriuretic peptides in the equine atrium. The distribution of immunoreactivity (IR) for cardiodilatin/atrial natriuretic peptide (CDD/ANP) and brain natriuretic peptide (BNP) was examined immunohistochemically and immuno-electron-microscopically in the equine atrium, using specific antibodies. In the immunohistochemical studies, IR-CDD/ANP and IR-pBNP-26 (porcine BNP-26 immunoreactivity) was detected in the cytoplasm of the auricular cardiocytes, but IR-hBNP-32 (human BNP-32 immunoreactivity) was not. The double immunogold labelling method for IR-hBNP-28 and IR-pBNP-26 revealed that gold particles of different sizes were located in th...
[Heart rate fluctuations in the horse at rest: (1) Investigation of heart rate changes by spectrum analysis]. The heart rate fluctuations at rest were studied in order to explore the emotionality of the horses by isolating the influence of the autonomic control. This paper presents a method of spectral analysis which was used to analyse the heart rate variability in the frequency domain. The heartbeat intervals were recorded during 1 h and a series of 1,024 heartbeats was extracted to compute a power spectrum of density. This was obtained by calculating the Fourier transform of the autocorrelation function of the series. This spectral analysis was applied to heart rate recordings in order to illustrat...
Prothrombotic events in the prodromal stages of acute laminitis in horses. Prothrombotic changes occurring in the prodromal stages of carbohydrate-induced laminitis were investigated. Hemostatic alterations were evaluated by determining platelet counts, platelet survival, activated partial thromboplastin time, one-stage prothrombin time, and monocyte procoagulant activity. Thrombosis of vessels in the hoof wall was evaluated by contrast arteriography and histologic examination. Of 5 horses, 4 became lame between 28 and 52 hours after carbohydrate administration. Mean platelet count in laminitis-affected horses was lower throughout the prodromal stages of laminitis, c...
Subcellular biochemical changes during the development of the small intestine of pony foals. To examine the postnatal development of equine small intestine, biopsy specimens of jejunal mucosa from 8 ponies, between 6 and 28 weeks old, were subjected to analytical subcellular fractionation and assay of organelle marker enzymes. Fractionation revealed a reduction in the particulate brush border component of beta-galactosidase (lactase) activity between 6 and 28 weeks, and a corresponding increase in soluble activity, although the reduction in mean specific activity was not significant. There also was a decrease in the proportion of brush border to soluble aminopeptidase N activity, a re...
