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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.
Serum testosterone levels in young normal horses. Serum testosterone levels were measured in normal young male horses (29 to 34 weeks old). No differences were found between gelded and intact males. The values for all the horses were low. On the basis of their testosterone levels, all the horses were prepubertal.
Plasma mepivacaine concentrations after caudal epidural and subarachnoid injection in the horse: comparative study. The venous plasma concentrations of mepivacaine were determined in 7 adult mares (420 +/- 17.1 kg) given an injection of a 2% solution of the hydrochloride at either the sacral (S2-3 to S5-C1) epidural space or the midsacral (S2-3) subarachnoid space. An average dose of 91.4 +/- 15.7 mg (4.6 +/- 0.8 ml) was needed to produce caudal epidural analgesia (CEA) and 26.7 +/- 5.4 mg (1.3 +/- 0.3 ml) to produce caudal subarachnoid analgesia (CSA). Maximal caudal analgesia extended from spinal cord segments S-1 to coccyx during CEA and CSA. The onset of analgesia as measured by response to superficial ...
Techniques and applications of transabdominal ultrasonography in the pregnant mare. To establish the feasibility of utilizing high-frequency ultrasound to image equine fetal development transabdominally, in vitro and in vivo observations were made. Three fetuses retrieved from mares that died from various causes were scanned in vitro to establish fetal images from various orientations. A total of 50 mares ranging in age from 4 to 16 years and representing various breeds were scanned intermittently from 100 days of gestation to parturition. Fetal parts, amniotic fluid, placental membranes, and motion patterns could be reliably identified. Fetal heart rates decreased from 180 b...
The effect of racetrack design on gait symmetry of the pacer. A survey of a western Canadian racetrack determined the superelevation and transition curves to be less than the cited design standards. High-speed cinematography was used to film seven Standardbred pacers as they proceeded around one curve of the track at racing speed and for each horse 19 temporal stride parameters were obtained from these films using a film analyzer system. Average velocities were calculated and the mean stride length was found to vary from 5.08 m to 5.77 m. In all frames analyzed the hind foot was observed to contact the track surface prior to the ipsilateral forefoot and ...
Effect of tyrosine modification on the biological and immunological properties of equine chorionic gonadotropin. The tyrosine residues of equine chorionic gonadotropin have been nitrated with tetranitromethane and the resulting effects on the biological and immunological activities of the hormone studied. All of the tyrosine residues in equine chorionic gonadotropin were found to react with tetranitromethane when a 100-fold molar excess of reagent was used or with an 8.6 molar excess in the presence of 5 M guanidine hydrochloride. Complete nitration abolished the biological activities and decreased the immunological activity of the hormone. The nitration of one tyrosine residue resulted in the loss of 70...
Isolation and partial characterization of bovine and equine factor D. Bovine and equine factor D were purified to apparent homogeneity as evidenced by a single protein staining band on 7.5-17.5% SDS-PAGE slab gels under both reducing and non-reducing conditions. An apparent mol. wt of 15,000 for bovine D and 22,500 for equine D were noted after SDS-PAGE gel analysis of both reduced and non-reduced preparations. A single polypeptide chain for both proteins was evidenced by the lack of any change in the electrophoretic mobility under each of these conditions. The bovine and equine D were enriched 3347- and 9447-fold, with a 20 and 29% yield of hemolytic activity, ...
Inspiratory airway CO2 loading in the pony. To determine if CO2-sensitive airway receptors are important in the control of breathing, CO2 was preferentially loaded into the respiratory airways in conscious ponies. The technique involved adding small amounts of 100% CO2 to either the latter one-third or latter two-thirds of the inspiratory air in an attempt to raise CO2 concentrations in the airway dead space independent of the arterial blood. Arterial blood gas tensions (PCO2 and PO2) and pH, as well as respiratory output (minute volume, tidal volume, and respiratory rate), were measured in a series of 20 experiments on 5 awake ponies. ...
Characterization of intrauterine mobility of the early equine conceptus. Intrauterine mobility patterns of the embryonic vesicle were characterized on Days 9 to 17 after ovulation in pony mares using real-time ultrasonography (n=5 or 7 mares per day). The location of the vesicle was determined by dividing the uterus into right horn, left horn, and body. Each uterine horn was further divided into three approximately equal portions (cranial third, middle third, caudal third), yielding seven segments (body plus three portions of each horn). Location of the vesicle within the uterus was recorded every five minutes for two consecutive hours (25 location determinations p...
[Interaction of bis-phosphorylated methanes with mammalian esterases]. The interaction of human erythrocyte acetylcholinesterase, horse serum butyrylcholinesterase and rat liver carboxylesterase with insecticides (RO)2P(O)SCH(COOEt)SP(O)(OR)2 (I) and (RO)2P(O)SCH(COOEt)OP(S)(OR)2 (II) was studied. The type I and II compounds were not hydrolyzed by carboxylesterase and inhibited the esterases irreversibly. A complex pattern of inhibition of acetylcholinesterase and butyrylcholinesterase by these compounds was caused by kinetically-manifested formation of an enzyme-inhibitor complex. The compounds I and II were more selective towards butyrylcholinesterase than towa...
Extenders for preservation of canine and equine spermatozoa at 5 degrees C. Two experiments were conducted to evaluate the effects of six extenders and three glycerol levels on the motility of sperm stored at 5 degrees C. Using a split-ejaculated design, semen from 10 dogs and 12 stallions was extended with egg-yolk-tris (EYT), egg-yolk-bicarbonate (EGB), Beltsville F-3 (BF-3), Cornell University (CUE), caprogen (CAP) and heated skim milk (SM) extenders. After cooling to 5 degrees C, additional extender containing 0% to 12% glycerol was added to provide a final concentration of 0%, 3% or 6% glycerol. Regardless of glycerol level, a higher (P<0.05) percentage of can...
The twitch in horses: a variant of acupuncture. The twitch procedure in horses attenuates the increase in the heart rate evoked by pain-inducing stimuli and the reaction of the animals to such stimuli. Endorphin systems are probably involved in the effectiveness of the twitch, since its action is blocked by naloxone and its application increases plasma concentrations of immunoreactive beta-endorphin. The mode of action of the twitch cannot be explained by the generally accepted theory of divertive pain and may resemble that of classical acupuncture.
The starch digestion test in the horse. Variable results were obtained when the starch digestion test was carried out on a suspected case of malassimilation in a horse. In order to re-evaluate this test, 15 starch digestion tests were carried out using 4 horses. Results showed a marked variation in the increase in plasma glucose levels between individual horses and especially between poor and good condition horses when the dose of starch was based on body mass. Results also suggest that a fixed dose of starch may give more consistent results.
Counterimmunoelectrophoresis for identification of equine urine. Counterimmunoelectrophoresis was evaluated as a method to distinguish urine of human origin from that of equine origin. The procedure used anti-equine serum and anti-human serum antibodies that had been solid-phase absorbed to eliminate species cross-reactivity. Counterimmunoelectrophoresis reliably detected contamination of equine urine by human urine to a level of 10% with a minimum sensitivity to about 2% contamination. Compared with double diffusion, counterimmunoelectrophoresis was approximately 10 to 15 times more sensitive in the detection of urine proteins.
Observations on structure and function of the equine mitral valve. The anatomy of the equine mitral valve and certain variations observed in 60 adult horses are described. The functional role of this valve, sited between the left atrium and the high pressure-generating left ventricle, is discussed in relation to its anatomical structure. A method of examining the left side of the heart post mortem is described.
Diamine oxidase from horse kidney: ionic strength dependence of stability and activity. Diamine oxidase was prepared from horse kidney by a procedure involving heat denaturation at 50 degrees C, ammonium sulfate fractionation, chromatography on hydroxyapatite and on G-200 Sephadex columns. This procedure gave about 1000 fold purification over the crude kidney cortex homogenate. The enzyme preparations thus obtained are stable only at high ionic strength. The effect on enzyme activity of salt concentration and various stabilizing agents have been investigated. The horse kidney diamine oxidase is irreversibly inhibited by carbonyl reagents and shows substrate specificity quite simi...
Hormonal responses to high and low planes of nutrition in weanling thoroughbreds. Growth-related skeletal diseases in young horses have been associated with high planes of nutrition, although the mechanisms underlying such an association have not been determined. It is likely that nutrition-induced effects on growth rate or growth quality involve the endocrine system. Hormonal and metabolic responses to the ingestion of meals containing either 80% (diet A) or 160% (diet B) of National Research Council energy and protein recommendations were examined in eight Thoroughbred weanling horses after 3 wk of dietary adaptation. After 24 h fasts, prefeeding serum concentrations of t...
Cardiodynamic variables and ventilation during treadmill exercise in ponies. We assessed the relationship of ventilation (VE) to cardiodynamic variables and CO2 transport in seven normal ponies during treadmill exercise. At 1.8, 3, and 6 mph, respectively, VE increased from 15 l/min at rest to 43, 51, and 86 l/min by 1 min and 48, 68, and 125 l/min by 8 min. In three ponies at the same work loads, cardiac output (Qc) increased from approximately 12 l/min at rest to 19.7, 28.1, and 40.3 l/min between 30-60 s (P less than 0.05) and then decreased by about 20% to a steady state by 3-4 min. Heart rate (HR) shows a similar biphasic response during exercise. Mean right ventr...
Temporal pattern of pulmonary gas exchange during exercise in ponies. We characterized the temporal patterns of pulmonary O2 consumption (VO2) and CO2 excretion (VCO2) in exercising ponies. We also assessed the cardiac, ventilatory, and hematologic contributions to the VO2-VCO2 changes during exercise. At five moderate treadmill work loads in normal ponies, VO2 and VCO2 generally increased progressively throughout the 1st min reaching, respectively, approximately 95 and 80% of steady state by 45-60 s. Between 1 and 1.5 min, Vo2 and Vco2 were either stable or they decreased 300-500 ml, but then each increased slightly, reaching steady-state levels between 3 and 5...
Potassium concentration in equine red blood cells: normal values and correlation with potassium levels in plasma. The concentration of potassium in plasma and in red blood cells was determined in 948 horses. The coefficient of correlation between the two parameters was low. In 436 of these horses, which were clinically healthy, the red blood cell potassium (RBCK+) levels did not fit within a normal distribution curve, but a bimodal distribution was observed with a section point at 90 mmol/litre. In 90 per cent of these normal horses, mean RBCK+ content was 97.5 mmol/litre. In the remaining 10 per cent, mean RBCK+ concentration was 93.8 mmol/litre. A subdivision into a 'low potassium group' and a 'high pot...
Relationship between potassium administration, hyperkalaemia and the electrocardiogram: an experimental study. Hyperkalaemia affected the equine myocardium. The minimum plasma potassium concentration required to induce electrocardiographic changes was 6.2 mmol/litre and severe cardiotoxic effects were observed at levels of 8.0 to 10.1 mmol/litre in this experimental situation. The most consistent sign of hyperkalaemia was broadening and flattening of the P wave, which was generally associated with a change in T waves in the chest lead from negative to positive. The more pronounced the hyperkalaemia, the less pronounced the P wave and the more peaked positive the T wave. Severe hyperkalaemia was associa...
Antitoxin levels in botulism patients treated with trivalent equine botulism antitoxin to toxin types A, B, and E. Serum levels of equine-botulism antitoxin to toxin types A, B, and E were measured in four type-A botulism patients who had received equine-botulism antitoxin. High circulating levels capable of neutralizing in excess of 1 X 10(8), 9 X 10(7), and 6 X 10(6) 50% mouse lethal doses of toxin of types A, B, and E, respectively, were detected. There was little depletion of type-A antitoxin even though two of the patients had circulating type-A toxin before treatment. The half-life for antitoxin persistence for one patient was calculated as being 6.5, 7.6, and 5.3 days for antitoxin types A, B, and E...
O2 transport in ponies during treadmill exercise. We assessed cardiovascular variables and blood O2 contents in order to characterize O2 transport in ponies during treadmill exercise. In normal ponies at 1.8, 3, and 6 mph, respectively, cardiac output (Qc) increased from 12 l/min at rest to maximum levels of 19.7, 28.7, and 39.9 l/min between 30 and 60 s. Qc then decreased to steady-state levels of 18.2, 24.6, and 32.7 l/min by 4 min. Heart rate (HR) showed a similar biphasic response in the 1st min of exercise. Systolic and diastolic arterial blood pressure (BP) decreased at the onset of exercise by 20-25 Torr (P less than 0.05) and then inc...
Relationship between intervertebral joint morphology and mobility in the equine thoracolumbar spine. The anatomical features of 21 equine thoracolumbar spines, obtained from horses with clinically normal backs, were examined and the results compared with recent data on the mobility of the joint complexes of the horse's spine. The thoracolumbar spine can be divided into four regions based upon the morphology of the joint complexes: the first thoracic intervertebral joint (T1-2), the cranial and mid thoracic region (T2-T16), the caudal thoracic and lumbar region (T16-L6) and the lumbosacral joint. The mobility of the intervertebral joints in each of these regions can be related to their morphol...
Partial amino-acid sequence and cysteine reactivities of cytosolic aspartate aminotransferase from horse heart. Cytosolic aspartate aminotransferase (L-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1) from horse heart has five cysteine residues, two of which can be titrated with 5,5'-dithiobis(2-nitrobenzoid acid) in the native enzyme with no impairment of catalytic activity. The rate of modification is unaffected by the presence of substrates. Reaction with N-ethylmaleimide leads to loss of catalytic activity, the rate of inactivation being increased by the presence of substrates. Peptides containing 361 amino-acid residues (about 88% of the total number in the protein) have been isolated and ali...
Microheterogeneity of type II cAMP-dependent protein kinase in various mammalian species and tissues. Excluding autophosphorylated species, at least six forms of the regulatory subunit of type II cAMP-dependent protein kinase (RII) from various mammalian tissues were identified by sodium dodecyl sulfate (SDS) gel electrophoresis of purified samples and of crude preparations photoaffinity labeled with 8-azido[32P] cAMP and by gel filtration. After autophosphorylation some heart RII forms termed type IIA (bovine, porcine, equine, and dog) shifted to a more slowly migrating band on SDS gels while others termed type IIB (rat, guinea pig, rabbit, and monkey) did not detectably shift. Both subclasse...
The regulatory peptide system of the large bowel in equine grass sickness. In recent years, distinct changes in regulatory peptides have been found in a number of gastrointestinal diseases. Grass sickness is a fatal disease of horses for which the etiology has yet to be fully ascertained. In this study, the peptide-containing nerves and ganglionic and mucosal endocrine cells of the ileum, colon and rectum were investigated in horses with sub-acute or chronic grass sickness and compared with normal controls using immunocytochemistry, at both the light and electron microscopical levels, and radioimmunoassay. A substantial loss of both peptide-containing cells and nerve...
