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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.
The applied pharmacology of azaperone in ponies. The butyrophenone tranquilliser, azaperone, was administered intramuscularly to ponies in five series of experiments, using a dose level of 0-4 mg/kg once and 0-8 mg/kg four times. An excellent or good sedative effect was usually obtained with both dose levels, but the response was more consistent with the higher dose. The onset of sedation was apparent within 10 min of administration, the maximal effect usually occurring between 20 and 60 min while sedation was no longer apparent after 2 to 6 h. Body temperature was reduced in all animals for at least 2 h and respiratory rate was increased in...
Hot film coronary artery velocity measurements in horses. Coronary velocity measurements have been carried out in anaesthetized, open-chest horses using a constant-temperature, hot-film anemometer system. L-shaped needle probes inserted by direct vessel puncture have been used to measure velocity profiles in the left common, left anterior descending (LAD), and left circumflex coronary arteries. The flow conditions were characterized by peak Reynolds numbers from approximately 200 to 1500 and values of the unsteadiness parameter from 3 to 10. These measurements indicate that in the left common coronary artery the profile is in general skewed towards t...
Normal and abnormal xylose absorption in the horse. The D-xylose absorption test was applied to clinically normal horses and to horses with signs of gastrointestinal disease. A dosage of 0.5 grams of xylose per kilogram of bodyweight was useful in detecting horses that absorbed the pentose abnormally. The clinical findings were correlated with gross and microscopic findings by biopsy and at necropsy. Gastrointestinal lesions associated with abnormal xylose absorption were classified as: 1) villous atrophy; 2) edema of the lamina propria or 3) necrosis of the lamina propria.
A comparison of techniques for the quantitative analysis of hyaluronic acid in equine synovial fluid. A comparison of methods of preparing the hyaluronic acid of equine synovial fluid for quantitative spectrophotographic analysis is presented. A new method is proposed which appears superior to the previous methods.
Ultrasonic measurement of arterial blood pressure in conditioned thoroughbreds. Indirect systolic and diastolic arterial pressure measurements of 456 Thoroughbred horses of various ages and sex stabled at 9 different race tracks were measured with an ultrasonic-Doppler device interfaced with a sphygmomanometer cuff. The mean systolic pressure was 111.8 +/- 13.3 mmHg and the mean diastolic pressure was 69.6 +/- 13.8 mmHg in this population.
Preliminary studies of pharmacological antigonism of anaphylaxis in the horse. Systemic anaphylaxis was induced in seven groups of ponies. Systemic hypotension, pulmonary hypotension, and apnea were observed in the control group. Suppression of anaphylaxis was achieved most efficiently with sodium meclofenamate followed by acetylsalicylic acid and diethylcarboamazine. Tripelennamine and methysergide reduced anaphylaxis minimally and burimamide not at all. The findings suggest that histamine and serotonin are of relatively low significance in equine anaphylaxis whereas kinins, prostaglandins and slow reacting substance may be more important.
A preliminary study of the measurement of plasma osmotic pressure in equine medicine. The normal plasma osmotic pressure was established in 205 Thoroughbred horses. Samples taken from horses suffering from a variety of diseases showed that measurement of this parameter might prove a valuable non specific test for assessing the severity of some diseases in which there are alterations in metabolism.
Horse-liver alcohol dehydrogenase and Pseudomonas testosteroni 3(17)beta-hydroxysteroid dehydrogenase transfer epimeric hydrogens from NADH to 17beta-hydroxy-5alpha-androstan-3-one. An exception to one of the Alworth-Bentley rules. In the reduction of 17beta-hydroxy-5alpha-androstan-3-one to the 3beta-alcohol, horse liver alcohol dehydrogenase utilizes the 4-pro-R hydrogen of NADH whereas the 3(17)beta-hydroxysteroid dehydrogenase of Pseudomonas testosteroni utulized the 4-pro-S hydrogen. These observations provide an exception to the rule proposed by Alworth and Bentley that with regard to the paired methylene hydrogens at C-4 of NADH and NADPH "the stereospecificity of a particular reaction is fixed and does not vary with the source of the enzyme preparation". It is also apparent that for these two enzymes, the selecti...
Effects of ovariectomy and season on plasma luteinizing hormone in mares. Six pony mares were ovariectomized (OVX) on day 16 of diestrus during June and July, 1972, to study short term changes in plasma luteinizing hormone (LH) concentrations. Plasma LH was higher (P less than .05) 3 days after OVX (1.76 ng/ml) than the day after OVX (1.01 ng/ml), and a gradual increase occurred over the first 2 weeks. Elevated plasma LH concentrations similar to mid-estrus levels were present from the 2nd to 11th week post-OVX. In another experiment, the same 6 OVX mares were bled once a month from February, 1973, to January, 1974, to study long-term changes in plasma LH in relatio...
The ultrastructure of the cell types in the endocrine pancreas of the horse. The islets of Langerhans of the equine pancreas were examined with the electron microscope after immersion or perfusion fixation. Five cell types could be distinguished after fixation by either technique: 1. A-cells, situated at the center of the islets, 2. B-cells, containing mostly "pale granules" and constituting the principal cell type of the periphery of the islets, 3. D-cells, also located mainly at the periphery of the islets, 4. G-cells, found at the edge of the islets and in the exocrine pancreas, and 5. S-cells, (small granule cells), which are relatively few in number and occur only...
Characterization of protein phosphokinase activities in horse thyroid nuclei. The distribution of protein phosphokinase (EC 2.7.1.37) activities has been established in horse thyroid nuclei. The presence of several enzyme activities has been demonstrated, two of which are clearly distinct. The first one acts on histone as substrate and is activated by cyclic AMP. Physico-chemical properties of this nuclear cyclic AMP-dependent histone kinase and of the cytosol histone kinase are different, demonstrating the absence of a contamination from the cytosol. The second enzyme acts on casein as substrate and is not stimulated by cyclic AMP POR CYCLIC GMP. The findings are consi...
Inactivation of horse liver alcohol dehydrogenase by modification of cysteine residue 174 with diazonium-1H-tetrazole. Diazonium-1H-tetrazole was tested as a potential active-site-directed reagent for amino acid residues involved in catalysis by alcohol dehydrogenase. In a novel reaction with a protein, diazonium-1H-tetrazole inactivated the enzyme selectively, and almost stoichiometrically, but reacting with the sulfur of a cysteine residue, Cys-174. As a model compound, the tetrazole adduct of free cysteine was prepared. Elementary and spectral analyses of the adduct were consistent with the structure 5-tetrazoleazo-S-cysteine. The adduct absorbs light with a maximun at 316 nm, and is destroyed by irradiatio...
Effects of training on biochemical values in standardbred horses. Effects of training at a regular, fixed, standard exercise load on venous lactic acid, mixed venous and arterial blood gases and pH, and serum muscle enzymes were determined on previously unconditioned, healthy, adult, Standardbred horses. Arterial and mixed venous blood gases, pH, and serum muscle enzymes did not change in a consistent manner during training. Venous lactic acid concentrations did increase significantly with training and may be of value for the biochemical evaluation of fitness in horses.
Acid-base values of standardbred horses recovering from strenuous exercise. Blood gases, lactic acid concentrations, and pH were measured in arterial and mixed venous blood in moderately conditioned Standardbred horses after a standardized exercise load of 1.6 km in 2 minutes, 40 seconds. Samples were obtained at rest, immediately after exercise, and at 3, 6, 15, 30, and 60 minutes after exercise. Arterial oxygen tension and mixed venous oxygen tension increased after exercise, reaching peak values at 6 minutes. Arterial oxygen tension returned to the resting (preexercise) value by 15 minutes, and mixed venous oxygen tension by 30 minutes. Arterial carbon dioxide tens...
Chemical mediators of anaphylaxis (histamine, 5-HT, and SRS-A) released from horse lung and leukocytes in vitro. Horses were sensitized to bovine plasma in Freund's complete adjuvant. Leukocytes, separated from venous blood, yielded histamine upon incubation with bovine plasma. Ioslated lung fragments incubated with bovine plasma liberated histamine and 5-HT, but not SRS-A. Pulmonary veins obtained from the same animals contracted to histamine, 5-HT and to antigen (Schultz-Dale reaction). Histamine and 5-HT probably contribute to immediate-type hypersensitivity in horses whereas the role of SRS-A is not proved.
Potassium metabolism in ponies. Potassium metabolism and some metabolic interractions of K, Mg and Ca were studied in a series of balance trials with ponies. The kidney was the primary pathway of K excretion. Increasing K intake markedly affected the renal excretion of K but had only small effects on fecal excretion. Increasing K intake increased retention and apparent digestibility of K. High levels of dietary Ca (3.4%) did not influence K metabolism but the highest level of Mg (.81%) increased the apparent digestibility of K. A level of 3.4% K did not decrease Mg, P or Ca digestibility and retention. The maintenance requir...
The effect of exercise on the lactic dehydrogenase and creatine kinase isoenzyme composition of horse serum. The distribution of lactic dehydrogenase, aldolase and creatine kinase in various horse tissues was determined. Using polyacrylamide gel electrophoresis the lactic dehydrogenase and creatine kinase isoenzyme composition of horse serum, taken before and after exercise, was studied. Horse tissue isoenzyme patterns were also obtained. By comparing tissue and serum patterns, skeletal muscle was found to be the tissue of origin of the increase in serum lactic dehydrogenase and creatine kinase observed after exercise.
Some assay restrictions on inferences made from determining hormones in horses, cows, and their fetuses. Often in developing hormone assays, hormones that may interfere with the assay by cross-reaction are not available for testing the validity of the assay. For example, horse TSH was unavailable to test for cross-reaction in an LH radioimmunoassay (RIA). The authors devised an indirect means of accomplishing the same goal, and the evidence from the indirect test of cross-reaction was at least as persuasive as a direct test might have been. Other examples are given of experiments where extensive effort was devoted to validation of steroid RIA, but there were substantial quantitative differences i...
