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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.
Single photon absorptiometry for the measurement of bone mineral content in horses. A safe, non-invasive method for the accurate measurement of bone mineral content in the third metacarpal bone of the horse is described. The technique involves scanning the bone with a single photon beam from an Americium-241 source. Data were obtained from the excised metacarpal bones from both forelimbs of 50 normal and seven lame horses. Measurements were made in vivo on eight normal and seven lame horses and on one experimental horse with osteopenia induced by partial weightlessness in a flotation tank. In the normal horses bone mineral content altered with age, particularly in the first s...
Copper, zinc and manganese concentrations in equine liver, kidney and plasma. Five groups of horses were fed different diets of known trace mineral concentration for a minimum of six months. Copper (Cu), zinc (Zn) and manganese (Mn) concentrations were measured in livers of 125 yearling horses and kidneys of 81 yearling horses as an assessment of trace mineral status. Plasma Cu and Zn determinations were made for all horses.Mean hepatic Cu concentrations of horses fed diets containing 6.9 to 15.2 mg Cu/kg dry matter (DM) feed were 0.27 to 0.33 mumol/g DM tissue. Plasma Cu concentrations ranged between 22.8 to 28.3 mumol/L. There was no simple mathematical relationship b...
Isolation and characterization of latherin, a surface-active protein from horse sweat. A protein, latherin, with unusual surface activity was isolated from horse sweat by gel filtration and ion-exchange chromatography. The protein has a Stokes radius, determined by gel filtration, of 2.47 nm, and in the ultracentrifuge sediments as a single species with S20,W 2.05 S, indicating an Mr of 24,400. On SDS/polyacrylamide-gel electrophoresis the molecule behaves as a single peptide chain of apparent Mr 20,000. Latherin contains a high proportion of hydrophobic amino acids (37.2%), and the leucine content (24.5%) is exceptionally high. The unusual composition of the protein may account...
Effects of acetylpromazine on the hemodynamics of the equine metatarsal artery, as determined by two-dimensional real-time and pulsed Doppler ultrasonography. Heart rate, blood velocity, volumetric blood flow, and arterial diameter for 10 horses given acetylpromazine were determined from measurements of the dorsal metatarsal artery 3 (the great metatarsal artery), using 2-dimensional real-time and gated pulsed Doppler ultrasonography. Acetylpromazine induced significant increases in arterial diameter (P less than 0.01) and volumetric flow rate (P less than 0.05)--all compatible with adrenergic blockade. There was a trend indicating that there was increased blood velocity. Heart rate was unchanged.
Immunoglobulin and specific antibody responses to Rhodococcus (Corynebacterium) equi infection in foals as measured by enzyme-linked immunosorbent assay. Humoral immune response to intestinal Rhodococcus (Corynebacterium) equi in horses was studied by enzyme-linked immunosorbent assay. Anti-R. equi immunoglobulin M (IgM), IgG, and IgA antibodies were demonstrated in the healthy horse population. Adult horse levels of anti-R. equi IgM and IgG antibodies were reached by 5 to 9 weeks of age in two healthy newborn foals. R. equi was recovered from the foals in the range of 10(3) to 10(4) per g of intestinal contents. A 1-week-old foal was infected with R. equi by mouth daily for 9 weeks. The foal did not show any clinical signs of illness. Anti-R. ...
Evaluation of leukapheresis and thrombocytapheresis in the horse. Continuous-flow centrifugation leukapheresis techniques were used to collect 300-ml volumes of leukocyte-rich plasma from 5 nonmedicated horses and from 5 corticosteroid-stimulated horses. White blood cell counts and differential counts were performed on the horses before (base line) and up to 48 hours after leukapheresis. Systemic administration of hydrocortisone increased numbers of total WBC and neutrophils and improved harvest of these cells. Nonmedicated horses had a mean yield of 3.38 X 10(10) leukocytes in the 300-ml volume. Stimulated horses yielded a mean of 6.88 X 10(10) leukocytes. ...
Effects of spontaneous, assisted, and controlled ventilatory modes in halothane-anesthetized geldings. Cardiopulmonary effects of spontaneous, assisted, and controlled ventilatory modes were determined with 6 young, healthy geldings anesthetized with halothane at a constant dose (1.3 minimum alveolar concentration). All horses were in lateral recumbency, and all modes of ventilation were studied at least once during each anesthetic exposure. Cardiac output did not differ between spontaneous and assisted ventilation modes, but both modes were associated with significantly (P less than 0.05) higher cardiac output than that with controlled ventilation. The PaCO2 differed significantly (P less than...
Neuromuscular and cardiovascular effects of atracurium in ponies anesthetized with halothane. Atracurium besylate, a recently developed, intermediate-duration acting, neuromuscular-blocking agent, was given to 15 halothane-anesthetized ponies to produce surgical relaxation (95% to 99% reduction of hoof twitch). All 15 ponies were given 3 injections; 8 of the 15 ponies were given 2 additional injections. Initial dosage of 0.11 +/- 0.01 mg/kg (mean +/- SD) and all subsequent injections of 0.052 mg/kg produced desired relaxation. Paralysis phase (maximum twitch reduction to 10% twitch recovery) lasted 24 +/- 5 minutes for the initial injection. Paralysis from subsequent injections lasted ...
Diurnal variation of dynamic compliance, resistance and viscous work of breathing in normal horses and horses with lung disorders. Dynamic compliance, airway resistance, viscous work and respiratory frequency were measured at intervals in horses over 12 h periods. Variation, daily averages and circadian patterns were recorded. Examinations were performed on 24 horses. They were divided into three groups: Normal horses, horses with chronic latent bronchitis and horses with manifest chronic obstructive pulmonary disease (COPD). Significant differences were found between the daily averages and the fluctuations when the normal group and the COPD group were compared. In most cases differences between all three groups were sign...
Induction of ovulation in anestrous mares with pulsatile administration of gonadotropin-releasing hormone. Four seasonally anestrous mares (Standardbred), housed under a nonstimulatory photoperiod of 8 hours light:16 hours dark, were administered gonadotropin-releasing hormone (GnRH) in a pulsatile pattern (50 or 250 micrograms of GnRH/hour) for 8 to 18 days during February and March 1985. Treatment with GnRH, irrespective of dose or month, induced an increase in serum luteinizing hormone from a mean pretreatment value typical of anestrus (0.58 +/- 0.02 ng/ml +/- SE) to 10.84 +/- 1.27 ng/ml on day 8 of GnRH treatment. Ovulation in the 4 mares occurred 8.8 +/- 0.7 days after the initiation of pulsat...
Gentamicin tissue concentrations in equine small intestine and large colon. Gentamicin sulfate (2.2 mg/kg of body weight, IV) was given to anesthetized horses. Jejunal and large colon tissue samples (1 g), serum, and urine were collected over a 4-hour period. Maximum gentamicin concentrations in serum (10.06 +/- 2.85 micrograms/ml) occurred at 0.25 hours after injection. Maximum gentamicin concentrations in the large colon (4.13 +/- 1.80 micrograms/ml) and jejunum (2.26 +/- 1.35 micrograms/ml) occurred in horses at 0.5 and 0.33 hours, respectively. Tissue concentrations decreased in parallel with serum concentrations and were still detectable at the end of the 4-hour ...
Ground reaction force patterns of Dutch Warmblood horses at normal walk. The ground reaction force patterns from 20 clinically sound Dutch Warmblood horses (Group A) were recorded at the normal walk. The data from four to 10 stance phases of each limb were computer averaged after normalisation to the animal's body mass and to the stance time. This analysis method allowed comparison of data from left and right fore- and hindlimbs within and between horses. The left-to-right symmetry in the reaction force peaks of contralateral limbs of one horse exceeded 90 per cent. The time in the stance phase at which the peaks occur were even more symmetrically distributed. A ch...
Effect of controlled exercise on libido in 2-yr-old stallions. Eight sexually inexperienced, 2-yr-old Morgan stallions were used in a consecutive two-phase design with two groups of four stallions each. Each phase lasted 16 wk, with semen collections every 14 d. Libido scores were assigned to stallions during each semen collection. Scores ranged from zero to four, with zero indicating minimum and four representing maximum libido. In Phase 1, four stallions received daily forced exercise for 16 wk, and the remaining four stallions were confined to box stalls. In Phase 2, the previously exercised stallions were confined to box stalls, and the non-exercised ...
An unusual pattern of Na+ and K+ movements across the horse erythrocyte membrane. Marked differences in the activities of three monovalent cation transport systems in horse versus human erythrocytes are reported. Whereas horse erythrocytes exhibit a 6-fold higher sodium-lithium countertransport, the unidirectional flux of potassium through the sodium pump is 3-4 times slower and the sodium-potassium cotransport system cannot be detected. In spite of this, horse and human cells are able to maintain similar Na+ and K+ gradients.
Heart rate and ECG response to twitching in Thoroughbred foals and mares. Changes of the heart rate and ECG to twitching were examined using 5 Thoroughbred foals at various ages and their mares. The effect of the heart rate decrease to twitching was significantly greater in the foals than in the mares. The decreased heart rate in the foals continued during and after the twitching. Changes of the T wave in the A-B lead ECG shown as enhancement of the negative ingredient of the T wave were observed both in the foals and in the mares, accompanied by a decrease in the heart rate during and/or after the twitching. Two out of the five foals showed second-degree A-V block ...
Equine endothelial cells in vitro. Certain in vitro culture conditions were determined for equine endothelial cells obtained from the aorta and pulmonary arteries. Cells were enzymatically isolated from the vessel lumen, using clostridial collagenase (2.5 mg/ml of Hanks's balanced salt solution) incubated at 37 C for 30 minutes. Cells were cultured in alpha minimum essential medium supplemented with plasma-derived and nonplasma-derived bovine fetal sera, endothelial cell-growth supplement, heparin, and antibiotics. Smooth muscle cell growth was not inhibited with nonplasma-derived animal sera, plasma-derived equine serum, or he...
Diseases of the liver. The ability to image the liver in horses can add valuable diagnostic information or aid in guided biopsy procedures. Anytime the size, shape, position, and texture of the liver can be determined, additional information about the horse's condition is gained. Conditions such as cholelithiasis, neoplasia, fibrosis can be detected ultrasonographically.
Ultrasound science for the veterinarian. In order to successfully sort out the information, both real and bogus, in an ultrasonic image, one must have a fundamental understanding of the physical and electronic events that produced the image. We have looked at the basic science, signal processing, some case examples of ultrasound science in practice, and some popular illusions. It is a good starting place for the newcomer to ultrasonic imaging.
J.B. Wolffe memorial lecture. Is the lung built for exercise? In summary, we have shown that the design of the pulmonary system from the architectural capacities of the lung parenchyma and respiratory muscles to the remarkable, multi-level neural integration of breathing pattern and respiratory muscle recruitment is clearly intended for the exercising state. Furthermore, the system shows remarkable capability for true adaptation, both phylogenetically and even within only a few generations within a species, when preservation of the organism's ability to survive and function is at stake. At the same time there are limits to the system's homeostatic capabi...
[Determination of the standard oxyhemoglobin dissociation curve in horses. Effects of temperature, pH and diphosphoglycerate]. The equine blood oxyhemoglobin dissociation curve has been traced in its entirety in standard conditions and the effects of temperature, pH and 2,3-diphosphoglycerate on this curve have been measured. When compared to that of human blood, the curve showed a higher oxygen affinity of hemoglobin (23.8 +/- 0.8 versus 26.6 mm Hg). The effect of the pH, expressed by d log P50/dpH, was found to be identical in man and horse (-0.47). The effect of temperature, however, expressed by d log P50/dT, proved to be lower in the horse (0.016 versus 0.024). The P50 showed an increase of 1 mm Hg each time 2,3-...
Equine thyroid function assessment with the thyrotropin-releasing hormone response test. The effect of thyrotropin-releasing hormone (TRH) on equine thyroid function was determined by quantifying serum thyroxine (T4) and 3,5,3'-triiodothyronine (T3) before and after TRH administration. Thyrotropin-releasing hormone was administered IV to adult horses (n = 5) and ponies (n = 6) at a dose of 1 mg or 0.5 mg, respectively. Serum T4 and T3 concentrations were determined before and 0.25, 0.5, 1, 2, 4, 6, 8, 12, and 24 hours after TRH administration. Serum T4 increased from a basal concentration of 24.4 +/- 8.7 ng/ml (mean +/- SD) to a maximum value of 48.2 +/- 10.2 by 4 hours after TRH ...
Antithrombin III activity in horses with large colon torsion. A chromogenic peptide substrate assay was used to determine serially plasma antithrombin III (AT III) activity in 4 groups of horses. Group I consisted of healthy, mature horses in which AT III activity was determined twice daily for 7 consecutive days. Groups 2 and 3 contained healthy horses in which AT III activity was monitored for 7 days after controlled, but varying, conditions of general anesthesia and surgery (median celiotomy). Group 4 was made up of patients with a presurgical diagnosis of colonic torsion. In healthy awake horses (group I), there was no difference in AT III values ove...
Effects of phenobarbital treatment on 3-methylindole toxicosis in ponies. To study the role of cytochrome P-450-dependent mixed function oxidase reactions in equine 3-methylindole (3MI) toxicosis, ponies were given 20 mg of phenobarbital/kg of body weight at 72, 60, 48, 36, and 24 hours before 100 mg of oral 3MI/kg to induce cytochrome P-450 or no treatment (controls). Maximal 3MI plasma concentration was decreased and clearance was faster in phenobarbital-treated ponies. Plasma 3MI was still detectable 12 and 36 hours after dosing in phenobarbital-treated and control ponies, respectively. Phenobarbital treatment induced a distribution phase with transition from a 1...
Occurrence and distribution of 5-S-cysteinyl derivatives of dopamine, dopa and dopac in the brains of eight mammalian species. The 5-S-cysteinyl derivatives of dopamine, dopa (3,4-dihydroxyphenylalanine) and dopac (3,4-dihydroxyphenylacetic acid) were synthesized and used as reference compounds in high performance liquid chromatography analyses of extracts from various brain regions of eight mammalian species. All three metabolites were detected in the brains of all the species studied. The regional distribution of the metabolites was similar to that of dopamine; the metabolite concentrations ranged from less than 0.1 percent to more than 1 percent of the dopamine level, the highest ratios generally being found in sub...
Spontaneous and stimulated adrenocorticotropin and vasopressin pulsatile secretion in the pituitary venous effluent of the horse. Plasma ACTH, arginine vasopressin (AVP), and catecholamines were measured at 5-min intervals in the pituitary venous effluent of the unanesthetized horse. Pulses of ACTH and AVP were found to be surprisingly brief (usually of less than 10-min duration) and frequent (averaging between 15-25 min). A highly significant relationship in the changes in concentration of these two hormones was demonstrated (P less than 0.0002) both at rest and after a mild hypoglycemic stimulus. Although there was also a significant correlation (P less than 0.005) between simultaneous plasma ACTH and AVP values the pu...
