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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.
Capacitation-like membrane changes and prolonged viability in vitro of equine spermatozoa cultured with uterine tube epithelial cells. Reliable capacitation of equine spermatozoa has been a major obstacle in the development of equine in vitro fertilization. Experiments were done to compare in vitro capacitation of equine spermatozoa by use of heparin/caffeine, calcium ionophore, uterine tube epithelial cell (UTEC)-conditioned medium, and direct culturing of spermatozoa with UTEC (coculturing). Capacitation-like changes, as determined by chlortetracycline membrane staining patterns, developed with UTEC-conditioned medium and coculturing, equivalent to that with calcium ionophore. Both of these treatments induced more (P < 0.05...
Determination of the optimal treadmill slope for reproducing the same cardiac response in saddle horses as overground exercise conditions. The purpose of this study was to define the most suitable treadmill slope for reproducing the same heart rate response as in horses being ridden on a track. Seven French saddle horses were exercised first on a level turf track and then on a treadmill. On the track the exercise test consisted of four periods of three minutes of increasing speeds at the trot and the gallop (96 to 600 m/minute). The treadmill exercise tests consisted of seven steps of increasing slope (0 to 9.6 per cent) at the trot (252 m/minute), followed, after an active recovery period at the walk with a 0 per cent slope, by ...
Stimulated decay of superoxide caused by ferritin-bound copper. The redox interaction between O2.- and ferritin cannot solely be regarded as as a Fe(II) release reaction. We demonstrate that native copper bound to horse spleen ferritin and apoferritin, stimulated the decay of O2.- in a catalytic reaction. Copper was determined by atomic absorption spectrophotometry. Decay of O2.- was monitored spectrophotometrically as the decrease in (A250-A360) at pH 9.5. The catalytic effect was linearly related to the copper content of the protein. Ferritin copper was less efficient than equimolar CuCl2, and iron-poor ferritin was more efficient than iron-rich ferritin...
Nucleation of the iron core occurs at the three-fold channels of horse spleen apoferritin: an EXAFS study on the native and chemically-modified protein. Extended X-ray absorbance fine structure measurements have been carried out on the initial Fe(III)-apoferritin complex at a Fe/subunit ratio of 2 in native and modified horse spleen apoferritin. Analysis of the data indicates that in the native protein the iron forms a protein-bound polynuclear cluster (Fe-Fe distance 3.4 A) with a first coordination sphere constituted by 5-6 low-Z atoms, e.g., nitrogen atoms, carboxylate-like ligands or oxo bridges between the iron atoms. Modification of Cys-126, a residue localized on the outer surface of the hydrophilic three-fold channels, with p-chloromer...
Equine fetal kinetics: Allantoic-fluid shifts and uterine-horn closures. Uterine filling by the conceptus and uterine constrictions and allantoic-fluid shifts after filling were studied by daily ultrasound examinations on Days 40 to 74 in 10 mares. Allantoic fluid was first detected at the extremities of the uterus on the following days: 1) tip of umbilical-cord horn, Day 60.0 +/-1.9 (mean +/-SEM); 2) tip of noncord horn, Day 64.8 +/-1.3; and 3) near cervix, Day 48.5 +/-1.3. Transient uterine constrictions with expulsion of allantoic fluid were detected in 37% of 271 examinations. Other end points were studied by weekly ultrasound examinations from Day 40 to term. ...
Oxidation of methionine residues in equine growth hormone by Chloramine-T. 1. Reactivity of methionine residues towards Chloramine-T was studied in the equine growth hormone. 2. With a 20.0-fold molar excess of reagent over methionine, full oxidation of the four residues of the protein is achieved. 3. Methionine 4 is the most reactive group, followed by methionines 72 and 178--methionine 123 being the less reactive residue. 4. As judged by circular dichroism spectra and binding assays, protein conformation and binding capacity to specific receptors remains unchanged even after full oxidation of all four methionine residues. 5. Results agree with data previously obtai...
Ultrasonographic measurement of stallion accessory sex glands and excurrent ducts during seminal emission and ejaculation. Accessory sex gland and excurrent duct activity of 10 stallions was visualized with transrectal ultrasonography during seminal emission and ejaculation. First and last penile urethral contractions were defined as the start (0 sec) and end of ejaculation, respectively. Duration of ejaculation (n = 63 ejaculations) averaged 6.15 +/- 2.98 sec. Penile urethral contractions occurred an average of 6.2 +/- 2.2 times per ejaculation. Right bulbourethral glands (n = 19 ejaculations) alternated repeatedly from ovoid to flattened, irregular shapes during ejaculation. Cross-sectional area of right bulbour...
Possible normokalemic variant of hyperkalemic periodic paralysis in two horses. Hyperkalemic periodic paralysis (HPP), characterized by intermittent episodes of muscle fasciculations, profound muscle weakness, and hyperkalemia, has been described in Quarter Horses, Appaloosas, and Paints. In previous reports, the hallmark of this syndrome has been the development of hyperkalemia during each episode. Two affected horses had episodes of paralysis without associated hyperkalemia, demonstrating that normokalemia during an episode otherwise consistent with HPP does not eliminate HPP as a diagnosis. This clinical presentation appeared to be a variant of HPP.
Effects of Aspergillus oryzae fermentation extract on in vitro equine cecal fermentation. The objective of this study was to examine the effects of Aspergillus oryzae fermentation extract on the in vitro equine cecal fermentation of soluble starch, amino acids/peptides, coastal bermudagrass hay, and alfalfa hay. Cecal contents were obtained from a cecally fistulated Quarter Horse gelding fed coastal bermudagrass and grain (70:30) either unadapted or adapted to dietary A. oryzae supplementation (2 g/d). Mixed cecal microorganisms were incubated in anaerobic media for either 24 h (soluble starch, amino acids) or 48 h (bermudagrass hay, alfalfa hay). A. oryzae was added to the incubat...
[Ganglioside GM3 from horse erythrocytes: structure and effect on cell proliferation]. An increase of the mouse fibroblast proliferation by ganglioside GM3 from equine erythrocytes is described. The structure of GM3 has been established on the basis of chemical methods, enzymatic degradation, GC-MS, as well as plasma desorption mass spectrometry and HPLC of 9-anthrylmethyl esters of gangliosides to characterize the long-chain base composition. The oligosaccharide moiety includes an N-glycolylneuraminic acid residue, whereas the main components of the lipid moiety are 20:1 sphingosine and 24:0 fatty acids.
Modulation of gonadotropin-releasing hormone-stimulated luteinizing hormone release in cultured male equine anterior pituitary cells by gonadal steroids. The objective of the present study was to determine whether the testicular steroids, i.e., testosterone (T), dihydrotestosterone (DHT), estradiol (E2), estrone (E1), and estrone sulfate (E1SO4), play a physiological role in regulating LH release in the male horse by direct actions at the anterior pituitary gland. Enzymatically dispersed anterior pituitary cells from stallions (n = 4) or geldings (n = 3) were cultured for 48 h in alpha-modified Eagle's medium containing 10% steroid-free horse medium. To determine the effects of the steroids on the LH response to GnRH, the cells were incubated f...
Equine plasma and blood volumes decrease with dehydration but subsequently increase with exercise. The effects of dehydration and 40 min of exercise at approximately 40% of maximal O2 consumption on plasma volume (PV) and blood volume (BV) were studied in six horses. Horses were exercised while euhydrated (C); 4 h after administration of furosemide (1.0 mg/kg i.v.; FDH), which induced isotonic dehydration; and after 30 h without water (DDH), which caused hypertonic dehydration. Dehydration resulted in decreases of 6.3 and 9.9% for PV and BV, respectively, with FDH and 10.7 and 8.5%, respectively, with DDH. During exercise in C, PV and BV increased by 12.7 and 20.0%, respectively; during exe...
Effects of dehydration on thermoregulatory responses of horses during low-intensity exercise. Effects of dehydration on thermoregulatory and metabolic responses were studied in six horses during 40 min of exercise eliciting approximately 40% of maximal O2 consumption and for 30 min after exercise. Horses were exercised while euhydrated (C), 4 h after administration of furosemide (FDH; 1.0 mg/kg i.v.) to induce isotonic dehydration, and after 30 h without water (DDH) to induce hypertonic dehydration. Cardiac output was significantly lower in FDH (144.1 +/- 8.0 l/min) and in DDH (156.6 +/- 6.9 l/min) than in C (173.1 +/- 6.2 l/min) after 30 min of exercise. When DDH, FDH, and C values we...
Role of decreased plasma volume in hematocrit alterations during incremental treadmill exercise in horses. Six intact (IN) and six splenectomized (SP) mares were subjected to an incremental exercise test to examine the role of decreases in plasma volume (PV) in the changes in hematocrit (Hct) normally seen with exercise. Each horse underwent an incremental exercise test in which it ran on a treadmill up a fixed incline of 6 degrees. The test started at a speed of 4 m/s, and speed was increased 1 m/s each min until heart rate reached a plateau. Blood samples were obtained at rest and at the end of the 4, 5, 6, and 7 m/s steps of the exercise test. Resting PV was greater (P < 0.05) in the IN group...
Effect of intramuscularly administered polysulfated glycosaminoglycan on articular cartilage from equine joints injected with methylprednisolone acetate. Intra-articularly administered, long-acting corticosteroids are a beneficial treatment for many equine joint disorders because they alleviate inflammation and signs of pain, but they also exert detrimental effects on the biochemical composition and morphologic features of articular cartilage. Chondroprotective drugs have been shown to mitigate some of the deleterious effects of intra-articularly administered corticosteroids on articular cartilage of laboratory animals. Twenty-one ponies were assigned at random to receive 1 of 3 treatments in the right middle carpal joint. Group-1 ponies (n = 8...
The acute effect of lowering plasma cortisol on the secretion of corticotropin-releasing hormone, arginine vasopressin, and adrenocorticotropin as revealed by intensive sampling of pituitary venous blood in the normal horse. The effect of an acute fall in plasma cortisol on the secretion of CRH, arginine vasopressin (AVP), and ACTH was studied using our nonsurgical technique for collecting pituitary venous (PV) blood from horses. PV blood from six mares was collected continuously and divided into 30-sec segments for 0.5 h before and during a 3-h infusion of metyrapone, an 11-beta-hydroxylase inhibitor. During treatment, plasma cortisol fell (P < 0.01) to a mean nadir of 15% of pretreatment levels, and 11-deoxy-cortisol rose (P < 0.02). Three mares became mildly agitated during treatment. Mean PV concentratio...
Effects of dehydration and rehydration on plasma vasopressin and aldosterone in horses. We have investigated the change in plasma vasopressin and aldosterone concentrations in Namib (desert-adapted) and in control horses from a subtropical region, during an acute 12% dehydration and during rehydration, while food was available. During dehydration, vasopressin concentrations increased significantly in both groups of horses, but the increase was significantly greater in Namib horses than in control horses. During rehydration, vasopressin levels fell, but fell significantly less in Namib horses. The change in vasopressin concentration correlated significantly with plasma osmolality ...
Serum osteocalcin concentration in horses treated with triamcinolone acetonide. The effect of triamcinolone acetonide (0.09 mg/kg of body weight, IM) on serum osteocalcin concentration was studied. Two groups of horses were investigated and included clinically normal horses (group 1, n = 5) and horses with chronic obstructive pulmonary disease (group 2, n = 5). Before treatment, results of a t-test did not reveal any significant difference in serum osteocalcin concentration between the 2 groups. After treatment, a significant (P < 0.05) decrease in serum osteocalcin concentration was observed for both groups. Osteocalcin concentration in individual horses reached a min...
Splenectomy alters blood pressure response to incremental treadmill exercise in horses. Six intact (IN) and five splenectomized (SP) mares were subjected to an incremental exercise test to examine the effects of splenectomy on blood pressure responses during exercise. During the test the horses ran up a 6 degree grade on a treadmill set at an initial speed of 4 m/s. Speed was increased 1 m/s every 1 min until heart rate (HR) reached a plateau. Hemodynamic data were collected continuously and analyzed for the last 18 s of the 4, 5, 6, and 7 m/s steps of the exercise test. There were no differences (P > 0.05) between the groups for resting means for any parameter measured in the...
Evaluation of the effect of alfentanil on the minimum alveolar concentration of halothane in horses. The effect of 3 plasma concentrations of alfentanil on the minimum alveolar concentration (MAC) of halothane in horses was evaluated. Five healthy geldings were anesthetized on 3 occasions, using halothane in oxygen administered through a mask. After induction of anesthesia, horses were instrumented for measurement of blood pressure, airway pressure, and end-tidal halothane concentrations. Blood samples, for measurement of pH and blood gas tensions, were taken from the facial artery. Positive pressure ventilation was begun, maintaining PaCO2 at 49.1 +/- 3.3 mm of Hg and airway pressure at 20 +...
Naloxone affects gastrointestinal functions and behaviour in horses. Clinical effects of the opioid antagonist naloxone were investigated in healthy horses. Naloxone caused a transient increase in the frequency of defecations, a softening of the faeces and alterations in the intensity of abdominal borborygmi. Total serum protein concentrations decreased. Behavioural changes like frequent yawning and flehmen occurred, heart rate decreased and respiratory rate tended to increase but no clinical signs of distress or pain were observed. It can be concluded that in healthy animals naloxone had only minor side-effects and could be used to investigate the physiologica...
Biomechanical considerations in the treatment of navicular disease. In recent years much attention has been paid to vascular studies of the navicular bone in health and disease; however, the relative importance of these studies has overshadowed biomechanical factors which may yet prove to be of importance. This paper outlines the pertinent anatomy, and discusses current concepts in the aetiology and pathogenesis of the disease. It describes the treatment regimens which are based on biomechanical considerations and compares the results of some currently employed techniques. All aspects of navicular disease remain controversial. This paper is not intended to rev...
Reconstitution of horse heart myoglobin with hemins methylated at 6- or 7-positions: a circular dichroism study. The reconstitution kinetics of horse heart myoglobin, as met-cyano derivative, with two synthetic hemins in which the 6- or the 7-propionate is replaced by a methyl group, has been investigated by circular dichroism, in order to gain information on the heme re-orientation process following the heme insertion into the globin pocket. The results obtained confirm that the preferred heme orientation places the sole propionate into the position occupied by the 6-propionate in the crystal structure, supporting the importance of the salt bridge occurring between this propionate and the basic CD3 resi...
In vivo investigation of communication between the distal intertarsal and tarsometatarsal joints in horses and ponies. The frequency of communication between the tarsometatarsal and distal intertarsal joints was investigated in 27 horses and 12 ponies. After the injection of diluted latex into the tarsometatarsal joints using the plantarolateral approach, the horses and ponies were walked for 200 meters. Latex was found in the distal intertarsal joints of 19 of 73 tarsi (26% communication) at necropsy. In 3 tarsi, latex was also found in the proximal intertarsal and tarsocrural joints.
