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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.
Oxygen deficit-oxygen debt relationships in ponies during submaximal treadmill exercise. The O2 deficit-O2 debt relationship in ponies was examined at two levels of treadmill exercise. Five healthy ponies exercised for 8 min at two work rates (WR):(1) 50 m/min at 6% grade and (2) 70 m/min at 12% grade. The O2 deficit and O2 debt were calculated using open-circuit measurement of pulmonary gas exchange during the transition from rest to steady-state exercise and during recovery from exercise. The O2 deficit was significantly lower (P less than 0.05) than the O2 debt at each of the two work rates. The means (+/- SEM) for the deficit and the O2 debt, respectively, in liters were: (1) ...
The equine colonic mucosal granular cell: identification and X-ray microanalysis of apical granules and nuclear bodies. The granular columnar epithelial cell of the equine dorsal large colon has been studied by transmission electron microscopy and X-ray microanalysis. Particular attention was focused on nuclear bodies commonly observed as central clusters of spherical, electron-dense inclusions within the nucleus. Ultrastructural morphology as well as X-ray microanalysis spectra reveal great similarity between colonic nuclear bodies and the numerous small granules of the apical cytoplasm in these epithelial cells. X-ray spectra of these cells were distinct from those of goblet cell mucous granules and mast cell...
The use of a passive hemolysis system to evaluate the complement activities of six mammalian species. A passive hemolysis assay system was developed which permitted comparisons of the hemolytic activities of complement (C) from six species. This system employs a single antigen and an antiserum raised in one species. Thus, variations resulting from different target antigens and those inherent in using antibodies (of different affinities and isotypes) raised in a variety of species were minimized. Of the erythrocytes (E) examined, those from horses and guinea pigs were most susceptible to lysis, and either would be suitable, as a tentative choice, for measuring C activity of a previously unstudi...
Ventilation-perfusion relationships in the standing horse: an inert gas elimination study. The multiple inert gas elimination technique was adapted for use in the conscious standing horse. The modifications included increased infusion rate of the inert gases (30 ml/min), extended infusion time (60 mins) in order to reach steady state, and construction of a nose mask mixing box system for collection of expired gas. Eight adult horses with a mean weight of 454 kg and a mean age of 6.1 years were studied while standing under resting conditions. Ventilation was 65.2 liters/min and cardiac output measured by thermodilution 40.2 liters/min. Systemic and pulmonary artery mean pressures wer...
Autotransfer of Day 4 embryos from oviduct to oviduct versus oviduct to uterus in the mare. Embryo autotransfer is defined as the collection of an embryo from and the transfer of this embryo into the same animal. The objectives of this study were to: 1) test the hypothesis that oviduct transport of the equine embryo from the oviduct into the uterus is not dependent on a unilateral embryo-corpus luteum interaction, 2) develop an embryo autotransfer technique for the mare and 3) compare the success rates of Day 4 embryos surgically autotransferred from the oviduct ipsilateral to ovulation to either the oviduct (n=10 mares) or the uterine horn (n=10 mares) contralateral to ovulation. Se...
Effects of semen fractionation and dilution ratio on equine spermatozoal motility parameters. Two experiments were conducted to examine the effects of semen fractionation and dilution ratio on motility parameters of stallion spermatozoa. In Experiment 1, three ejaculates from each of three stallions were divided into sperm-rich (SR) and sperm-poor (SP) fractions to determine the difference in sperm concentration. Mean sperm concentration in SR fractions (349.5 x 10(6)/ml) was greater (P < 0.001) than that of SP fractions (96.9 x 10(6)/ml). In Experiment 2, three ejaculates from each of two stallions were divided into SR and SP fractions. Fifty percent of the original volume of SR fr...
Assessment of neutrophil migration, phagocytosis and bactericidal capacity in neonatal foals. Comparison of neutrophil function was made between 8 clinically normal pony foals (3 to 7 days of age), and their dams. Random migration, stimulated migration to zymosan-activated serum, bacterial phagocytosis and bactericidal capacity of neutrophils were determined in vitro. Random migration was greater (P less than 0.01) and stimulated migration was less (P less than 0.01) in foals than in their dams. Bacterial phagocytosis and bactericidal capacity of neutrophils were not different (P greater than 0.05) between foals and mares. Results of this study suggested that neonatal foals have altere...
Management of twin conceptuses by manual embryonic reduction: comparison of two techniques and three hormone treatments. One hundred mares carrying twin conceptuses between gestation days (GD) 12 and 30 were assigned to 4 groups. Group-1 mares (n = 20) were given a placebo (sterile saline solution, IV, and sesame oil, IM). Group-2 mares (n = 32) were given a single dose of progesterone (625 mg, IM) in sesame oil. Group-3 mares (n = 28) were given multiple progesterone treatments (625 mg, IM) at 6-day intervals until GD 42. Group-4 mares (n = 20) were given a single treatment of flunixin meglumine (500 mg, IV) and progesterone (625 mg, IM). Each group was further assigned to equal subgroups A and B according to t...
Oral administration of ascorbic acid to horses. The effects of oral administration of high doses of ascorbic acid on plasma concentrations were investigated in both experimental Thoroughbred horses and those within racing stables. A single oral dose (20 g) did not result in any increase in plasma concentrations. However, daily administration of either 4.5 g or 20 g doses resulted in significant increases in plasma concentrations. Monthly variations in plasma ascorbate concentrations were found in both supplemented (20 g daily) and unsupplemented stables. It is concluded that oral supplementation with ascorbic acid is a satisfactory route to...
Effects of physiologic and pharmacologic agents on serum prolactin concentrations in the nonpregnant mare. Four studies were conducted to evaluate the effects of several physiologic and pharmacologic agents on serum prolactin concentrations in the nonpregnant mare. An increase in prolactin measured in response to administration of thyrotropin-releasing hormone (TRH; 50 micrograms, iv) was found not to vary (P = .20) in mares in estrus compared with mares in diestrus (5 to 10 d post-ovulation). Administration in the dopamine receptor blocker, metoclopramide (25 or 100 mg, im), rapidly increased serum prolactin, and the response was dependent on dose administered (total prolactin measured for 420 min...
Measurements of muscular microcirculation by laser Doppler flowmetry in isoflurane and halothane anaesthetised horses. The cardiovascular function of horses was less depressed during anaesthesia with isoflurane than during anaesthesia with halothane. Muscular microcirculation measured by laser Doppler flowmetry was significantly greater in horses anaesthetised with isoflurane.
Ischaemia induced development of functional coronary collateral circulation in ponies. The response of coronary collaterals in nine ponies subjected to repeated reversible occlusions (2 min duration, 30 min interval) of the left anterior descending coronary artery was studied at rest. Each pony was instrumented with a Doppler flowmeter and hydraulic cuff occluder around the left anterior descending coronary artery, left ventricular subendocardial sonomicrometers, and a left ventricular micromanometer. Initial occlusions increased end diastolic myocardial segment length by 3% and decreased segment systolic shortening, stroke work, and velocity of shortening by 103%, 95%, and 79% ...
Energy utilization and blood traits of ponies fed fat-supplemented diets. The digestibility and heat production values for three fats of different origin were determined. Four pony geldings (225 kg) were used in a study consisting of four successive digestion trials utilizing a 4 X 4 Latin square design. The four dietary treatments were basal alone and supplemented with 15% corn oil, blended fat or inedible tallow. The blended fat was composed of a mixture of animal and vegetable fats. A 7-d preliminary period preceded a 7-d total fecal collection period for each trial. Heat production values were obtained by indirect calorimetry and calculated from oxygen consumpti...
Central to peripheral sound propagation in excised lung. The time it takes audible sound to travel from the trachea to the pleura in five intact, excised horse lungs and one dog lung inflated with several gases was measured. Regression estimates of sound speed at total lung capacity (TLC) using straight line distance from the carina to the pleura are: helium, 775 +/- 60.5 m/s (means +/- 95% confidence limits); air, 282 +/- 23.5; carbon dioxide, 219 +/- 25.5; sulfur hexafluoride, 142 +/- 43.5. With the exception of sulfur hexafluoride, these speeds are 15%-20% less than the free-field speed of sound in each gas. Total airway length did not predict ti...
Effect of ranitidine on gastric acid secretion in young male horses. Gastric cannulas were placed surgically in 5 young male horses. After a 2-week recovery period, horses were studied once a week. Horses were fasted for 24 hours, and gastric fluid output was collected for 5 continuous hours. Volumes were recorded every 15 minutes, and pH and hydrogen ion concentration were determined in an aliquot from each period. In 10 basal experiments, using 5 horses, volume, pH, and hydrogen ion concentration were continuously variable. Mean acid output was 45.1 +/- 2.02 microEq/15 min/kg (mean +/- SEM). In 6 experiments, using 3 horses, 0.5 mg of ranitidine/kg of body we...
In vitro febantel transformation by sheep and cattle ruminal fluids and metabolism by hepatic subcellular fractions from different animal species. Febantel and one of its main metabolites, febantel sulphoxide, are chemically modified to only a slight extent when incubated in vitro with sheep and cattle ruminal fluids; other major metabolites, fenbendazole and oxfendazole, are respectively, oxidized to oxfendazole and reduced to fenbendazole. Febantel is negligibly metabolized by hepatic cytosol fractions but microsome preparations effect more extensive metabolic transformations. Important differences in this respect were found between microsome preparations from rat, horse, pig, cattle, sheep, chicken and trout livers.
Systemic distribution of blood flow in ponies during 1.45%, 1.96%, and 2.39% end-tidal isoflurane-O2 anesthesia. Effects of 1.1, 1.5, and 1.8 minimal alveolar concentration (MAC) isoflurane-O2 (1.45%, 1.96%, and 2.39% end-tidal isoflurane, respectively) anesthesia on cardiac output, blood pressure, and blood flow to the brain, thyroid glands, adrenal glands, kidneys, and splanchnic organs were examined in 9 healthy isocapnic adult ponies. Tissue blood flows were studied using 15-micron diameter radionuclide-labeled microspheres that were injected into the left ventricle, and comparisons were made with data obtained from ponies in the conscious state. Isoflurane anesthesia caused dose-related reduction in...
Can the product of the theta gene be a real globin? A new member (theta 1, or psi alpha) of the alpha-globin gene family has recently been identified in a number of species. In higher primates the theta 1 gene has all the structural features apparently necessary for expression, and it appears to have long been under strong selective constraints which suggests that it could still be, or recently have been, a functional gene. No corresponding 'globin' has yet been identified, however. In some other species, galago and rabbit for example, the theta 1 and psi alpha genes have accumulated enough inactivating mutations for them to be considered genui...
Effects of a nine-month endurance training programme on muscle composition in the horse. Muscle biopsy samples were collected from the middle gluteal muscle of seven horses undergoing a nine-month endurance training programme. Samples were collected before the programme began and again after three, six and nine months of training. A fifth sample was collected three months after training ceased. Serial muscle sections were reacted histochemically for myosin adenosine triphosphatase after either acid (pH 4.3 and 4.6) or alkaline (pH 10.3) pre-incubation, and muscle fibres identified as type I, IIA, IIB or IIC. The oxidative capacity of individual fibres was assessed, using the reduc...
Definition of 15 equine leucocyte antigens. Fifteen equine leucocyte antigens were defined by absorption and titration analysis of alloantisera obtained by natural sensitisation through pregnancy and by planned experimental immunisation. Definitive sera were tested on the cells of 90 unrelated horses and members of eight equine families. The family data suggested that 13 specificities were coded by a single locus (first locus) and one specificity (Eq 14) was coded by a second linked locus. The remaining specificity (Eq 7) was controlled by a third locus unlinked to the first or second loci. Tests on the cells of unrelated horses showed ...
Distribution of cephapirin into a tissue chamber implanted subcutaneously in horses. The pharmacokinetics of cephapirin sodium and its distribution into a tissue chamber implanted subcutaneously in the neck of mature horses are described. Cephapirin was administered as an intravenous bolus dose of 20 mg/kg. The serum concentration vs time curve was best described by a two-compartment open model. Cephapirin disappeared from serum rapidly (t1/2 beta = 18.8 min), and had only a modest volume of distribution (Vd(area) approximately equal to 346 mg/kg, Vd(ss) approximately equal to 204 ml/kg). Total clearance was also rapid (approximately equal to 13 ml/min.kg). Concentrations of t...
Exercise-induced pulmonary haemorrhage in the horses: results of a detailed clinical, post mortem and imaging study. VII. Ventilation/perfusion scintigraphy in horses with EIPH. Detailed post mortem examination of the lungs of horses with exercise-induced pulmonary haemorrhage (EIPH) has demonstrated significant small airway disease and intense bronchial arterial proliferation in the dorsocaudal lungfields. The purpose of this study was to investigate ventilation and perfusion distribution in the lungs of a similar group of horses to compare changes in the live animal with the previously reported post mortem findings. Thoracic radiography and ventilation/perfusion (V/Q) scintigraphy were performed on five racing Thoroughbreds with recent histories of EIPH. Parametric ...
Induction and characterization of acrosome reaction in equine spermatozoa. Equine spermatozoa were incubated in a chemically defined medium for 8 hours. The medium preserved spermatozoal viability, as assessed by total spermatozoal motility, progressive spermatozoal motility, and spermatozoal exclusion of eosin stain. Effects of time and divalent cation ionophore, A23187, on the occurrence and character of the spermatozoal acrosome reaction were determined. Two light microscopic assays, a triple-stain technique and a chlortetracycline fluorescence assay, were calibrated with transmission electron microscopy for detection of the acrosome reaction. Incubation time and ...
