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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.
Prerace venous blood acid-base values in standardbred horses. The administration of sodium bicarbonate (NaHCO3) or 'milk shakes' to Standardbred horses before racing is widespread. This study analysed nonrace day (CTL) and prerace venous acid-base values from Standardbred horses racing in Pennsylvania (PA) and New Jersey (NJ). Mean +/- s.d. CTL bicarbonate (HCO3) and base excess (BE) values, for a group of horses stabled during the 1993 racing season at Pocono Downs, Pennsylvania, were 28.6 +/- 1.9 and 2.6 +/- 1.7 mmol/l, respectively. In the same population of horses, mean +/- s.d. values for prerace HCO3- and BE values were 33.1 +/- 2.8 and 7.0 +/- 2.3...
Accuracy of Accusport for measurement of lactate concentrations in equine blood and plasma. The aim of this study was to investigate correlations between lactate concentrations in equine whole blood and plasma measured with Accusport1 and Yellow Springs Instruments (YSI2) (2300) methods. The effect of packed cell volume (PCV) on the accuracy of Accusport was also investigated. Blood samples were collected from Thoroughbred horses at 5-10 min intervals after a treadmill exercise test. Blood was added to NaEDTA (for PCV measurement) and to 2 tubes containing lithium heparin anticoagulant (for lactate assays). At concentrations greater than 10 mmol/l, Accusport1 greatly underestimated t...
Pharmacokinetics of ketoprofen in the donkey (Equus asinus). The pharmacokinetic parameters of ketoprofen were determined in four donkeys after a single intravenous injection of a dose of 2.2 mg/kg body weight. The total body clearance (ClB) was 414.0 +/- 98.70 ml/h/kg (mean +/- SD), the volume of distribution at steady state (Vss) 263.10 +/- 55.43 ml/kg and the elimination half-life 1.30 +/- 0.75 h. These values were compared to those obtained in horses.
Methanogenesis in monogastric animals. Studies of methanogenic bacteria present in monogastric animals are still scarce. Methanogens have been isolated from faeces of rat, horse, pig, monkey, baboon, rhinoceros, hippopotamus, giant panda, goose, turkey and chicken. The predominant methanogen in all except the chicken and turkey is species of Methanobrevibacterium. The chicken and turkey harbour species of Methanogenium. In pig the population of methanogenic bacteria is more than 30 times as dense in the distal colon as in the caecum. This finding is in agreement with the finding that the rate of methane production is much higher in...
Minimal redistribution of pulmonary blood flow with exercise in racehorses. We determined the spatial distribution of pulmonary blood flow at rest and during increasing levels of exercise (34, 59, and 90% of maximal oxygen consumption) in Thoroughbred racehorses (n = 4) using 15-microns fluorescent microspheres. After the horses were killed, the lungs were flushed free of blood, removed, air-dried at total lung capacity, and sliced into isogravitational planes, which were sampled in a systematic fashion for three-dimensional reconstruction. The fluorescence was measured for quantification of blood flow. Mean pulmonary blood flow heterogeneity (expressed as a coefficie...
Assessment of autonomic nervous function by power spectral analysis of heart rate variability in the horse. We studied power spectral analysis of heart rate (HR) variability in the horse, with the hypothesis that the quantitative information provided by the spectral analysis of HR variability reflects the interaction between sympathetic and parasympathetic regulatory activities. For this purpose, electrocardiogram, blood pressure (BP) and respiratory (Resp) waveform were simultaneously recorded from Thoroughbred horses (3-5 years old) and analyzed by power spectrum. There were two major spectral components at low-frequency (LF) and high-frequency (HF) bands for HR variability. The peak of Resp varia...
Cardiopulmonary effects of desflurane in ponies, after induction of anaesthesia with xylazine and ketamine. Cardiopulmonary parameters were measured in 12 ponies (small horses) before anaesthesia and, following induction with xylazine and ketamine, during maintenance of anaesthesia with desflurane. In six of the ponies (group A) anaesthesia was maintained for three hours with desflurane at an end-tidal concentration of 7.4 per cent. In the other six ponies (group B), anaesthesia was maintained in the same way for one hour and then the effects of end-tidal desflurane concentrations of 7.4 per cent and 9.6 per cent with and without artificial ventilation were investigated. In group A ponies the arteri...
Use of the relationship between blood lactate and running speed to determine the exercise intensity of horses. Eight thoroughbred horses, trained for racing competition, were subjected to a standardised incremental speed test to determine the relationship between their blood lactate concentrations and running speed. Between 14 days before and 14 days after completing the standardised exercise test, the horses were timed for runs of 2000 to 6000 m. The blood lactate concentration after each run was measured and compared with the blood lactate concentration predicted from the individual horse's blood lactate-running speed relationship curve determined from the standardised exercise test. The relationship...
Age and breed differences in thyroid hormones, insulin-like growth factor (IGF)-I and IGF binding proteins in female horses. A survey with horses was conducted to determine whether plasma concentrations of triiodothyronine (T3), thyroxine (T4), insulin-like growth factor (IGF)-I and IGF binding proteins (IGFBP) change as horses grow, mature sexually, and age. Jugular blood was sampled from Standardbred fillies and mares at ages 0, 1, 7, and 14 d, at 1, 2, 4, 5, 6, and 9 mo, and at 5 to 8 and 16 to 22 yr (n = 5 to 18). In a second survey, we measured the same variables in eight breeds of horses with markedly different adult body sizes, from Miniatures to Friesians. Plasma T3, T4, and IGF-I were determined by radioimm...
Gene transfer by adenovirus in smooth muscle cells. We report adenovirus-mediated gene transfer into airway smooth muscle cells in cultured cells and organ-cultured tracheal segments. Incubation of cultured rat tracheal myocytes with virus (5 x 10(8) pfu/ml) for 6 h resulted in beta-galactosidase expression in 94.8 +/- 2.5% of cells (n = 4). Following incubation of thin (less than 200 microns diameter) equine trachealis muscle segments with virus in organ culture (5 x 10(8)-5 x 10(10) pfu/ml) the average expression of the Lac Z gene was approximately 19 +/- 10% (n = 9). Expression was markedly improved, however, in segments from neonatal rats (...
Surface plasmon resonance studies of complex formation between cytochrome c and bovine cytochrome c oxidase incorporated into a supported planar lipid bilayer. II. Binding of cytochrome c to oxidase-containing cardiolipin/phosphatidylcholine membranes. Complex formation between horse heart cytochrome c (cyt c) and bovine cytochrome c oxidase (cco) incorporated into a supported planar egg phosphatidylcholine membrane containing varying amounts of cardiolipin (CL) (0-20 mol%) has been studied under low (10 mM) and medium (160 mM) ionic strength conditions by surface plasmon resonance (SPR) spectroscopy. Both specific and nonspecific modes of cyt c binding are observed. The dissociation constant of the specific interaction between cyt c and cco increases from approximately 6.5 microM at low ionic strength to 18 microM at medium ionic strength, ...
Alterations in colonic arterial and venous plasma neuropeptide concentrations in horses during low-flow ischemia and reperfusion of the large colon. To measure colonic arterial (CA) and colonic venous (CV) plasma neuropeptide concentrations during low-flow ischemia and reperfusion of the large colon in horses. Methods: 10 adult horses. Methods: CA and CV plasma samples collected from anesthetized horses during experimentally induced low-flow colonic ischemia and reperfusion were assayed for vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), and substance P (SP), using radioimmunoassays. In 6 anesthetized horses, colonic ischemia (20% of baseline (BL]) was maintained for 3 hours, then blood flow was restored an...
Effects of altered FIO2 on maximum VO2 in the horse. Although the horse is considered an elite athlete with a specific VO2max some 2-4 times higher than man, maximal O2 transport is compromised both by moderately severe arterial desaturation and by failure to extract all O2 from blood perfusing exercising muscle. This prompted the present study to ascertain whether correction of arterial desaturation would proportionally augment VO2max and, if so, would O2 extraction behave in a manner predicted by diffusional transport limitation. Six two year old thoroughbreds were exercised to VO2max on a treadmill each on three separate occasions breathing g...
Osteonal structure in the equine third metacarpus. In studying the flexural fatigue properties of the equine third metacarpal (cannon) bone, we previously found that the dorsal region was weaker monotonically, but more fatigue resistant, than the lateral region. Fatigue resistance was associated with fracture surfaces which demonstrated that secondary osteons had "pulled out" of the surrounding matrix; this never happened in lateral specimens. We therefore became interested in the osteonal structure of this bone, and began to study its birefringence patterns in circularly polarized light. We found that the predominant type of secondary osteon ...
Comparison of media and sera used for in vitro culture of equine superficial digital flexor tendon explants. To compare the effects of different commercial nutrient media and sera on protein synthesis and maintenance of cellular density in cultures of the equine superficial digital flexor tendon (SDFT). Methods: 8 healthy 2- to 4-year-old horses. Methods: First Dulbecco's modified Eagle's medium, Ham's F12 nutrient mixture, RPMI 1640 medium, minimum essential medium with Earle's salts, minimum essential medium with Hanks' salts, and a Dulbecco's modified Eagle's medium/Ham's F12 nutrient mixture with 10% fetal bovine serum (FBS) were compared. Then FBS, fetal equine serum, and donor horse serum, each...
Involvement of nitric oxide in inhibitory neuromuscular transmission in equine jejunum. To evaluate the role of nitric oxide (NO), vasoactive intestinal peptide (VIP), and a transmitter acting through an apamin-sensitive mechanism in mediating inhibitory transmission in the equine jejunal circular muscle, and to determine the distribution of VIP-and NO-producing nerve fibers in the myenteric plexus and circular muscle. Methods: Circular muscle strips were suspended in tissue baths containing an oxygenated modified Krebs solution and attached to isometric force transducers. Responses to electrical field stimulation (EFS), tetrodotoxin, the NO antagonists L-N-nitro-arginine-methyl-...
[Changes of serum enzymes, lactate and hemoglobin concentrations in the blood of young trotting horses due to training exertion]. Until the age of about 2 years, trotters normally grow up on pasture without any kind of training. In the stud farm Lindenhof (Templin, Germany), however, these first 2 years are used for a special fitness training for the young animals: 2-3 times a week, a group of the yearlings is forced to run a distance of about 1700 m on a track at an average speed of up to 10 m/s. Until now, little was known about changes of blood parameters which may occur during such special exercise. This study therefore investigated the activity of selected serum enzymes (aspartate-amino-transferase (AST), alanine-am...
The modulus of elasticity of equine hoof wall: implications for the mechanical function of the hoof. During normal weight-bearing and locomotion, the equine hoof wall deforms in a consistent pattern; the proximal dorsal wall rotates caudo-ventrally about the distal dorsal border and there is latero-medial flaring posteriorly. The aim of this study is to examine whether there are regional differences in the modulus of elasticity of hoof wall material and whether such differences correlate with the pattern of deformation which occurs in vivo. The modulus of elasticity of equine hoof wall was determined in tension and compression for samples from six forefeet. Samples were tested at the mid-poin...
In vitro and in vivo effects of activated macrophage supernatant on distal limb wounds of ponies. To determine whether monokines produced by activated rabbit peritoneal macrophages can inhibit development of exuberant granulation tissue formation in distal limb wounds in ponies. Methods: Randomized block. Methods: 5 castrated male ponies, 2 to 6 years old and weighing 140 to 190 kg. Methods: In vitro activity of cell-free rabbit peritoneal macrophage supernatant was determined after incubation of fibroblasts from the flank and the distal portion of limbs of horses and ponies. Tritiated thymidine was then added, and after reincubation, radioactivity was measured. After creation of a 4-cm2, ...
Structure of equine infectious anemia virus proteinase complexed with an inhibitor. Equine infectious anemia virus (EIAV), the causative agent of infectious anemia in horses, is a member of the lentiviral family. The virus-encoded proteinase (PR) processes viral polyproteins into functional molecules during replication and it also cleaves viral nucleocapsid protein during infection. The X-ray structure of a complex of the 154G mutant of EIAV PR with the inhibitor HBY-793 was solved at 1.8 A resolution and refined to a crystallographic R-factor of 0.136. The molecule is a dimer in which the monomers are related by a crystallographic twofold axis. Although both the enzyme and t...
Theoretical predictions of end-capillary PO2 in muscles of athletic and nonathletic animals at VO2max. Characterizing the resistances to O2 transport from the erythrocyte to the mitochondrion is important in understanding potential transport limitations. A steady-state model of this process was developed to predict the minimum (critical) end-capillary PO2 required to prevent hypoxia at maximal O2 consumption (VO2max) in a circular region of tissue surrounding the venular end of a capillary. Capillary density was used as a measure of O2 delivery, and mitochondrial density was used as a measure of O2 consumption. The effects of oxyhemoglobin dissociation kinetics and diffusion facilitation by hem...
Effects of transporting horses facing either forwards or backwards on their behaviour and heart rate. The effects of transporting horses facing either forwards or backwards were compared by transporting six thoroughbred horses in pairs in a lorry on one journey facing in the direction of travel, and on another journey facing away from the direction of travel, over a standard one-hour route. Heart rate monitors were used to record their heart rate before, during and after the journey and the horses' behaviour was recorded by scan sampling each horse every other minute. The average heart rate was significantly lower (P < 0.05) when the horses were transported facing backwards, and they also t...
Integrative model for predicting thermal balance in exercising horses. A theoretical integrative model was developed to determine the heat balance of horses working in a given environment. This model included the following parameters: metabolic heat gain, solar heat gain, evaporative heat loss due to sweating, respiratory tract heat loss, radiation from the body and heat gain or loss due to convection and conduction. The model developed in this study includes an unique approach for estimating heat loss via evaporation of sweat from the animal's skin surface. Previous studies modelling evaporative heat dissipation were based on the volume of sweat loss. While it i...
Modified ventilated capsule for the measurement of sweating rate in the exercising horse. Modification of a ventilated capsule technique for the measurement of sweating rate (SR) is described for application in an exercising horse. The plastic capsule was sealed against the coat of the horse. Dry air was blown through the capsule over the skin and the change in absolute humidity (g/m3) between air entering and leaving the capsule was used to calculate SR. The effect of flow rate on the response characteristics of the system was investigated and measured over a range of sweating rates in a group of horses completing a short exercise test. Repeatability of SR measurements made at 2 s...
The relationship between respiratory exchange ratio, plasma lactate and muscle lactate concentrations in exercising horses using a valved gas collection system. A valved gas collection system for horses was validated, then used to examine the relationship between the respiratory exchange ratio (RER), and plasma and muscle lactate in exercising horses. Four healthy Standardbred horses were trained to breathe through the apparatus while exercising on a treadmill. Comparisons of arterial blood gas tensions were made at 3 work levels for each horse, without (control), and with the gas collection system present. At the highest work level, the arterial oxygen tension (PaO2) was significantly lower (P < 0.05), and the arterial carbon dioxide tension (PaCO...
