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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.
Changes in blood flow distribution in equine lungs induced by anaesthesia. The distribution of blood flow to the lungs was measured with labelled microspheres injected into horses before and during anaesthesia. Anaesthesia was induced with glycerol guaiacolate ether and ketamine, and maintained with the spontaneous breathing of halothane in oxygen. In a preliminary group of six horses, flow distribution was observed during anaesthesia in sternal, dorsal and right lateral recumbency. In two other groups, each of four horses, the flow distribution with time during either sternal or right lateral recumbency was observed. A small, constant proportion of the 15 micron dia...
Variation of fiber types in the triceps brachii, longissimus dorsi, gluteus medius, and biceps femoris of horses. The distribution of type-I and type-II fibers in 9 different parts of the musculi triceps brachii, longissimus dorsi, gluteus medius, and biceps femoris was studied to determine whether biopsies from these muscles give reliable information. All 4 investigated muscles were not homogeneous in their fiber-type distribution. Large differences existed among different muscle parts. The percentage of type-I fibers increased toward the deeper and cranial parts of the muscles. In the same zone of the gluteus muscle, differences of 30% were found for type-I fibers. Therefore, results obtained by biopsie...
Changes in blood constituents accompanying exercise in polo horses. There have been several studies of biochemical changes in horses doing intense exercise such as Thoroughbred and Standardbred racehorses and in horses performing exercise over a long period of time such as endurance horses and three-day eventing horses, but we are not aware of studies with polo horses. Blood samples were taken from 18 polo horses at rest, immediately after playing 2 chukkers of indoor polo, and after a 15 minute rest period. Each horse was studied at 2 different games. The blood samples were analyzed for lactic acid, protein, sodium, potassium, chloride, calcium, phosphorus, H...
Intravenous histamine administration in ponies with recurrent airway obstruction (heaves). Pulmonary function and airway reactivity to IV histamine were measured in a group of ponies with a history of recurrent airway obstruction (heaves) and their age-, weight-, and gender-matched controls. Ponies were studied during a period of clinical remission (period A), after exposure to a barn environment (period B), and twice during a 2-week recovery phase (periods C and D). At periods A, C, and D, PaO2, dynamic compliance (Cdyn), pulmonary resistance, tidal volume, respiratory frequency, and the log dose of histamine required to reduce Cdyn to 65% of base-line value (log ED65Cdyn) of princ...
Antigenic determinants of acylphosphatase from porcine skeletal muscle. Analysis of the quantitative precipitin reaction of acylphosphatase from porcine skeletal muscle with rabbit antiserum indicated the presence of at least two antigenic determinants on the porcine enzyme molecule. Immunological cross-reactivities of acylphosphatases from equine and rabbit skeletal muscles were examined. In double immunodiffusion with the antiserum, the precipitin lines of the porcine and equine enzymes completely fused, while the rabbit enzyme gave no precipitin line. The reaction between the 125I-labeled porcine enzyme and its antibody was inhibited to the same extent by the p...
Hybrids from equine LH: alpha enhances, beta diminishes activity. LH hybrids were prepared by combining eLH alpha and eLH beta with the corresponding subunits of oLH, pLH and hCG. Recombinants were isolated by gel filtration and assessed by SDS-polyacrylamide gel electrophoresis under both dissociating and non-dissociating conditions. All combinations of subunits produced hybrid LH molecules. Hybrids prepared by combining eLH beta with oLH alpha, pLH alpha or hCG alpha were very inactive in rat radioligand and Leydig cell in vitro bioassays. Hybrids prepared with eLH alpha were very active in both assays. The greatest potentiating activity was observed when ...
[Hyalurodinase activity of beta-hemolytic streptococci of the Lancefield group C]. A total of 110 strains of beta-hemolytic streptococci, belonging to serogroup C (Lancefield), isolated from horses (71 S. zooepidemicus, 27 S. equisimilis and 12 S. equi) as well as 5 reference strains were tested for their ability to produce hyaluronidase. The determinations were carried out in a culture test on agarose gel and in a liquid test system (turbidity test according to DiFerrante). The results of both methods used showed that the three Streptococcus species could be differentiated by the relative quantitative determination of hyaluronidase activity. S. equisimilis strains produce 5...
Plasma and serum concentrations of phenylbutazone and oxyphenbutazone in racing Thoroughbreds 24 hours after treatment with various dosage regimens. The plasma and serum concentrations of phenylbutazone (PBZ) and oxyphenbutazone were measured in 158 Thoroughbred horses after various doses of PBZ wer given. All horses were competing or training at racetracks in various parts of the country. All horses used in the study had not been given PBZ 24 hours before they were placed on a specific dosage schedule. Samples were collected 24 hours after the last PBZ administration. Four grams of PBZ were given daily by stomach tube, paste, or tablet for 3 days. On day 4, 24 hours before sample collection, an IV dose of 2 g of PBZ was given, regardless ...
Estrogen metabolites in equine ovarian follicles: gas chromatographic-mass spectrometric determinations in relation to follicular ultrastructure and progestin content. Equine follicular fluid was aspirated at various developmental stages (viable, preovulatory and atretic) determined by ultrastructural study. Estrogens and progestins were analyzed by gas chromatography-mass spectrometry associated with stable isotope dilution. Progesterone and 17-hydroxyprogesterone were the principal progestins of the preovulatory and viable follicles. Among the catechol estrogens, 2-hydroxy-estradiol was particularly abundant in the preovulatory follicle and its definitive identification was made by the scan of a full mass spectrum.
Ultrasound as a tool for assessment of bone quality in the horse. A simple non-invasive method is described for calculating the transverse apparent velocity of sound of horse bone. This was achieved, both in vivo and at post mortem examination using the metacarpal bone and its covering soft tissue. On 34 post mortem specimens (ie, 68 limbs) from horses older than one year an average measurement of 2802 +/- 37 (1sd) m/sec was obtained. There were changes noted according to age and at different sites on the shaft of the metacarpus. The highest readings were obtained in the proximal shaft where the cortex was thickest. The velocity values gradually decreased to...
The biosynthesis of 3 beta-hydroxy-5,7-androstadien-17-one by the horse fetal gonad. Horse fetal gonadal tissue was incubated with 3 beta-hydroxy-5,7-pregnadien-20-one and 5,7-cholestadien-3 beta-ol and it was shown that both substrates were converted to 3 beta-hydroxy-5,7-androstadien-17-one. These findings support the proposal that in this tissue there is a 5,7-diene pathway producing 3 beta-hydroxy-5,7-androstadien-17-one, the putative precursor of equilin in the placenta.
Iron deposition in apoferritin. Evidence for the formation of a mixed valence binuclear iron complex. A preliminary EPR investigation of iron accumulation in apoferritin has identified paramagnetic species generated during the early stage of iron deposition within the apoprotein shell. A featureless resonance at g' = 4.3, attributable to solitary high spin Fe3+ ions bound to the protein, is generated when Fe(II) is added to apoferritin at a level of 0.5 Fe/subunit (12 Fe/molecule) followed by air oxidation. This resonance accounts for 36% of the added iron. The remainder is EPR-silent and is probably present as oligomeric Fe3+ species. The intensity of the g' = 4.3 signal is reduced 3-fold upo...
The effect of training and physical exercise on the energetic metabolism of equine erythrocytes. Erythrocytes, due to their simple metabolic processes, differ greatly from nucleated
cells. Their main metabolite of glycolysis is 2,3-Diphosphoglycerate (2,3-DPG), which
serves also as an energy store for producing ATP in the pyruvate kinase reaction. 2,3-DPG
modifies also the affinity of haemoglobin for oxygen (4). Increase in the concentration of
2,3-DPG, ATP and body temperature, or a decrease in the pH value of blood causes
decreased affinity of haemoglobin for oxygen as blood transverses muscle capillaries,
facilitating oxygen delivery. In equine erythrocytes, the level of ATP is s...
Fascial compartments of the equine crus. The deep fascia of the equine crus was dissected grossly and separated into 2 layers, the superficial and deep laminae of the deep fascia. Attachments of these fascial laminae to the tibia and fibula formed 5 separate osteofascial compartments: cranial, lateral, caudal deep, caudal intermediate, and caudal superficial. Cranial tibial vessels and the deep peroneal nerve entered the cranial compartment through separate fascial hiatuses; this may predispose the equine crus to the occurrence of compartmental syndromes with clinically recognizable neural deficits.
Laboratory evaluation of aqueous humor in the healthy dog, cat, horse, and cow. Using routinely available clinical laboratory methods, aqueous humor samples were evaluated from 12 healthy dogs, 15 healthy cats, 7 healthy horses, and 6 healthy cows. Aqueous humor was almost acellular; cells that were present had degenerated beyond recognition. Protein concentration was low; only albumin was detectable on electrophoresis. Creatine phosphokinase and lactate dehydrogenase isoenzymes were not detected. Artifacts induced by sampling were insignificant compared with alterations in aqueous humor composition that occur with ocular diseases.
Turbidimetric measurement of IgG(T) in the serum of healthy Thoroughbreds and ponies. The turbidimetric analysis of IgG(T) in the serum of horses is described. Reference values are provided for 'worm-free' ponies (2.6 +/- 0.7 g/litre), stabled Thoroughbreds two years old and over (4.1 +/- 1.3 g/litre), grazing Thoroughbred broodmares (7.1 +/- 2.4 g/litre) and regularly wormed adult and young ponies grazing pasture contaminated with intestinal parasite eggs and larvae.
Evaluation of the wick catheter as used to measure intracompartmental muscle pressure in equine muscle. The use of the wick catheter to measure intracompartmental muscle pressure in equine muscle was documented. The presence of muscle compartments involving the extensor carpi radialis muscle and the long head of the triceps brachii was demonstrated by anatomic dissection and radiographic technique. The wick catheter was capable of accurately measuring pressures within both of these compartments. Furthermore, the wick catheter was sensitive to pressure changes resulting from external compression of muscle compartments. Manipulation of systemic blood pressure and PaCO2 in 1 anesthetized horse did ...
[Comparative characteristics of the vitreous body proteins in vertebrates]. Using disc-electrophoresis in polyacrylamide gel and immunochemical methods, studies have been made on proteins from the vitreous body of mammals (albino mouse, rat, guinea pig, pig, dog, cat), birds (hen), amphibians (the frog Rana ridibunda) and fish (the perch Perca fluviatilis). It was found that vitreous body proteins in man and animals include both the specific proteins and those of the blood serum. During evolution, specific antigens of the vitreous body attained strict species specificity, although some of them preserved the initial properties.
Direct current stimulation of bone production in the pony: observations with a diaphyseal osteotomy model. Electrically induced osteogenesis exhibits a dose response curve and can induce bone formation in the absence of trauma and in nonunions. Electrically induced osteogenesis, using direct electric current (DC) in a third metacarpal diaphyseal osteotomy model, in conjunction with internal fixation and postoperative loading, was investigated. Twelve young adult ponies of mixed sex were divided into 2 treatment groups (A and B) of 3 stimulated and 3 controls each and evaluated, using a specifically designed procedure. Stimulated ponies in both groups were given 20 microA of DC via an implanted bone...
Patterns of secretion of luteinizing hormone, follicle stimulating hormone and testosterone in stallions during the summer and winter. Samples of jugular blood were drawn from each of five stallions every 15 min for 12 h during the summer and winter to determine the short-term fluctuations in plasma concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone. Concentrations of LH and FSH were generally not pulsatile, although one stallion exhibited three distinct pulses in these hormones during the winter. In general, patterns of secretion of all three hormones were similar in both seasons and the number of significant rises in hormonal concentrations did not differ between seasons. Concent...
Pharmacokinetic studies of theophylline in horses. The pharmacokinetics of theophylline were determined in Standardbred trotters after single intravenous and oral administration. A bi-exponential equation was fitted to the intravenous data and a tri-exponential equation to the oral data. The biological half-life of theophylline was found to be 14.8 h, the volume of distribution 1.02 l/kg and the total plasma clearance 0.86 ml/kg/min. The oral absorption of the drug was complete (bioavailability 108%) and rapid (absorption half-life 0.4 h).
Arterial to end-tidal CO2 tension and alveolar dead space in halothane- or isoflurane-anesthetized ponies. The correlation between end-tidal partial pressure of CO2 (PETCO2) and arterial (PaCO2) was determined for spontaneously breathing ponies under halothane or isoflurane anesthesia. The PETCO2 was useful as a trend indicator of PaCO2 during the first 60 minutes of halothane or isoflurane anesthesia when PaCO2 values were less than 60 to 70 mm of Hg. Halothane anesthesia lasting greater than 90 minutes was associated with PaCO2 values in excess of 60 to 70 mm of Hg, a large arterial- to end-tidal PCO2 difference (PaCO2-PETCO2) and a significant increase in alveolar dead space. These effects were ...
Maximal anaerobic (lactic) capacity and power of the horse. Blood lactate concentrations were determined in 16 horses (three Thoroughbreds, seven Standardbreds and six polo ponies) before and 5 mins after they galloped over distances of 200, 300 and 400 m at maximal speed. The highest net lactate concentration (delta Lamax) of 14 to 15 mmol/litre was attained by the polo ponies and the highest speed by the Thoroughbreds. The maximal rate of lactate production (delta Låmax) was about 35 mmol/litre X min for the polo ponies and 20 to 25 mmol/litre X min for the Standardbreds and the Thoroughbreds. Values for delta Lamax and delta Låmax were similar to ...
Capacitively coupled electrical stimulation of bone healing in the horse: in vivo study with a Salter type IV osteotomy model with stainless steel surface electrodes. The use of capacitively coupled low-voltage signals for stimulation of osteogenesis has been reported in a variety of animal models. Electrically induced osteogenesis was investigated with a capacitively coupled electric field on a radius (distal-lateral orientation) osteotomy model, in conjunction with internal fixation and postoperative loading. Twelve adult horses of either sex were allotted to 2 groups of 6; 1 group was given electrical stimulation and the other served as controls. A low-voltage high-frequency capacitively coupled electrical signal was locally and continuously applied to t...
Force development during sustained locomotion: a determinant of gait, speed and metabolic power. This paper develops three simple ideas about force development during sustained locomotion which provide some insights into the mechanisms that determine why animals change gait, how fast they can run, and how much metabolic energy they consume. The first idea is that the alternate stretch-shorten pattern of activity of the muscles involved in locomotion allows muscle-tendon units to function as springs, affecting the amount of force a given cross-sectional area of muscle develops, and the metabolic requirements of the muscles for force development. Animals select speeds and stride frequencies...
Variant specific opsonization of Trypanosoma evansi measured by luminol-dependent chemiluminescence. Using luminol-dependent chemiluminescence (LCL), the specificity of antibodies to variable antigen type (VAT)-populations of Trypanosoma evansi was studied in four infected ponies. Trypanosomes of each wave of parasitemia were isolated and multiplied in irradiated mice. Their opsonization by serum collected during the infection was investigated with LCL and results for isolated VAT-populations are shown in the paper. Antibodies specific to each VAT-population were first found three days after the maximum of a parasitemic wave. There was no cross reactivity between different VAT-populations. LC...
