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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.
Isolation, partial identification and quantitative determination of four guaiphenesin glucuronides in plasma and urine of the horse by high-performance liquid chromatography. The isolation, partial identification and quantitative determination of four guaiphenesin glucuronides in plasma and urine of the horse is described. The identity of the glucuronides was checked by UV and fluorescence spectrophotometry, by NMR spectrometry and by mass spectrometry after permethylation. The applicability of the procedure to pharmacokinetic studies is demonstrated.
Continuous caudal epidural anesthesia in the horse. A technique for continuous caudal epidural anesthesia in the horse was developed in trials involving 8 healthy adult horses. The injection site was the first intercaudal (intercoccygeal) space. A Huber point directional needle (Tuohy or Hustead) with a stylet was preplaced into the epidural space, used as a guide for an epidural catheter, and then removed, leaving the catheter in situ in the epidural space. A 2% solution of lidocaine hydrochloride was used as the anesthetic agent at an initial dose of 8 ml for an adult animal (474 kg to 560 kg). Repeated 4-ml doses were administered immediatel...
Hemodynamics before and after conversion of atrial fibrillation to normal sinus rhythm in horses. Hemodynamic measurements were obtained from 17 horses with atrial fibrillation or flutter. Eight horses had atrial fibrillation of unknown duration. In 7 horses, atrial fibrillation developed during anesthesia. Atrial flutter developed during recovery from anesthesia in 2 horses. Hemodynamic measurements were considered normal in 7 of 8 conscious horses with atrial fibrillation. Cardiac output was decreased and pulmonary arterial blood pressure and right atrial pressure were increased in 1 conscious horse which had signs of congestive heart failure. Arterial blood pressure decreased in 5 of 7 ...
Sequence of the high-activity equine erythrocyte carbonic anhydrase: N-terminal polymorphism (acetyl-Ser/acetyl-Thr) and homologies to similar mammalian isozymes. The amino acid sequence of the high-activity equine erythrocyte carbonic anhydrase (CA-II) has been determined. Two different N-termini are noted, the C1 form having an N-acetyl-serine and the C2 form an N-acetyl-threonine. The sequence of the equine enzyme is most homologous to the human CA-II isozyme, with 224 of the 259 residues being identical.
Production of cutaneous analgesia by electroacupuncture in horses: variations dependent on sex of subject and locus of stimulation. Cutaneous pain thresholds to pinprick, pinch, and heat stimuli were quantified during control and electroacupuncture trials in 23 horses. Pain thresholds for 8 areas of the body during control trials (no needles) were statistically compared with pain thresholds measured in the same areas of the same horse when given electroacupuncture treatment. Statistically significant increases of pain threshold were interpreted as induced analgesia and occurred mainly in 5 areas of the trunk, but not in the head or extremities. Analgesic efficacy varied between sexes and among 3 groups of points chosen fro...
Alpha 2-macroglobulin from horse plasma. Purification, properties and interaction with certain serine proteinases. alpha 2-macroglobulin was isolated by polyethylene glycol precipitation, gel filtration on Sephacryl S-300 and DE-52 cellulose chromatography, with 20% yield. The preparation obtained was homogenous as tested by biochemical and immunological criteria. Its molecular mass was estimated at 800,000, comprising of four identical subunits. The isoelectric point of our preparation was 4.8 and two molecules of serine proteinases per 1 molecule of inhibitor were bound.
Measurement of diffusion of uncharged molecules in articular cartilage. The diffusion of glucose (180 M.W.), inulin (5,000 M.W.) and dextran (20,000 M.W.) into mature bovine and equine articular cartilage was studied. Concentration profiles were determined using a one-dimensional experimental configuration and the diffusion coefficient and partition coefficient calculated from a theoretical model. Glucose was found to diffuse the fastest, followed by inulin and dextran. The partition coefficient was similarly ordered. The rate of diffusion was found to decrease with increasing diffusion time, indicating a dependence on solute concentration. No time variation was e...
Impedance monitoring of equine intestinal motility. Myoelectrical and myomechanical activities of the distal portion of the jejunum and pelvic flexure were studied in 7 ponies, using permanently implanted monopolar and bipolar stainless steel electrodes. Dental acrylic embedded recording electrodes were surgically sutured to the serosal surface of the distal portion of the jejunum and pelvic flexure. Myoelectrically, regular spike bursts and irregular spike bursts were observed in the jejunum. Short spike bursts and long spike bursts were recorded and associated with spike potentials, using impedance recording techniques. Electrical and mechani...
Development and characterization of a homologous radioimmunoassay for equine prolactin. A specific and sensitive homologous radioimmunoassay has been developed for equine prolactin, suitable for measuring prolactin concentrations in serum of horses. The sensitivity of the assay ranged from 0.4 to 0.6 ng/ml and the intra- and inter-assay coefficients of variation averaged 6.9 and 15.4%, respectively, for five doses of hormone. Cross-reactivity with other mammalian and nonmammalian prolactins and growth hormones was less than 20 and 0.3%, respectively. Cross-reactivity with equine growth hormone was less than 0.07%. Equine serum and pituitary extracts showed parallel dilution-respo...
Effects of halothane anesthesia on equine liver function. Effects of halothane anesthesia were investigated in ponies prepared surgically with chronic external biliary fistulas (T tubes) to determine the effects on liver function and biliary excretion during 2 hours of anesthesia. Four studies were performed on 2 ponies, 2 to 6 months after surgery with the enterohepatic circulation held intact between studies. Intravenous bile acid infusion was used to maintain steady-state bile flow, bilirubin, and bile acid excretion during each study. Compared with the immediate 2-hour preanesthesia values (base line), halothane caused a 138% increase in bilirubi...
Intrauterine movement of the early conceptus in barren and postpartum mares. The equine embryonic vesicle has been shown to be highly mobile prior to day 15, moving from one horn to the other many times per day. In Experiment 1, intrauterine mobility patterns of the vesicle were compared between barren and postpartum mares on days 12, 13, or 14, using an ultrasound instrument. Location of the vesicle (left horn, right horn, body) was determined every five minutes during six two-hour trials in each group. Averaged over all trials, the vesicle moved from one horn to the other 1.1 times per two-hour trial. There were no significant differences between barren and postpartu...
Effects of in vivo administration of testosterone propionate on in vitro production of follicle-stimulating hormone and luteinizing hormone by pituitaries of pony mares. The in vitro incorporation of [3H]leucine into immunoprecipitable follicle-stimulating hormone (FSH) and luteinizing hormone (LH) was assessed for pituitaries from pony mares treated with testosterone propionate (TP) or oil (controls). Mares were treated every other day with TP (n = 4) at 350 micrograms/kg of body weight or with an equivalent volume of oil (n = 4). One day following the sixth injection of TP, each mare received an intravenous injection of gonadotropin releasing hormone (GnRH) at 1.0 micrograms/kg body weight and was bled frequently for 4 h. Treatment of mares with TP reduced F...
Pain perception and alleviation in animals. In the last 2 decades there have been substantial advances in our knowledge of the scientific basis of the mechanisms of pain. Nociceptors or pain receptors are widespread in the skin and tissues of animals; chemical mediation of nociceptor excitation may provide a key for understanding the peripheral phenomena related to pain. The expression of pain in animals involves multiple ascending and descending branches, as well as specialized pain-signaling mechanisms in the spinal cord. The importance of these different pathways varies with species and circumstances. Endogenous neural systems in the...
Motility of the distal portion of the jejunum and pelvic flexure in ponies: effects of six drugs. Bipolar stainless steel electrodes were surgically implanted in 4 ponies to record myoelectrical and mechanical activity of the distal portion of the jejunum and pelvic flexure. After determining normal activity, the effects of neostigmine, xylazine, flunixin meglumine, dipyrone, panthenol, and atropine sulfate were determined. Flunixin meglumine, dipyrone, and panthenol had no effect on the motility of the jejunum or pelvic flexure. Xylazine and atropine sulfate decreased motility of the distal portion of the jejunum and pelvic flexure, with atropine sulfate having a greater effect and lastin...
Time of ovarian follicular recruitment in cyclic pony mares. An experiment was carried out on pony mares to establish the time of the oestrous cycle at which ovarian follicles are recruited for ovulation. In one group (n=7), the cycle was interrupted at the preovulatory stage by removing the preovulatory follicle; in another group (n=13) the cycle was interrupted at day 6 of the luteal phase by inducing luteolysis with a prostaglandin injection (PG). In a subgroup (n=7) of those given PG, the ovary not bearing the corpus luteum was removed at the time of injection. A further group (n=6) served as surgical controls. The interval to the next ovulation and...
Dynamic strain similarity in vertebrates; an alternative to allometric limb bone scaling. Galileo (1638) observed that "nature cannot grow a tree nor construct an animal beyond a certain size, while retaining the proportions which suffice in the case of a smaller structure". However, subsequent measurement has shown that limb bone dimensions are scaled geometrically with body size (Alexander et al., 1979a), and that the material properties of their constituent bone tissue are similar in animals over a wide range of body weight (Sedlin & Hirsch, 1966; Yamada, 1970; Burstein et al., 1972; Biewener, 1982). If, as suggested in previous scaling arguments (McMahon, 1973; Biewener, 19...
Cardiovascular and pulmonary effects of recumbency in two conscious ponies. Respiratory dead-space, tidal volume, respiratory rate, blood gases, cardiac output, heart rate and arterial and pulmonary arterial blood pressures were measured in two conscious, trained ponies in the standing position and in left lateral recumbency. The ponies were reluctant to remain lying down for more than about 20 mins but the reason for this did not become apparent. Tidal volume was reduced during recumbency but the respiratory rate increased, tending to maintain the minute volume at about that of the standing animal. Arterial carbon dioxide tension did not change significantly from sta...
[An analysis of reproducibility in the determination of the activity of selected enzymes in the blood serum of horses]. Single biochemical analyses can be used for the diagnosis of animal diseases only with the knowledge of the effects that may distort the single result. The study of the repeatability of analyses is described in the four basic enzymes (AST, ALP, GMT, LD), which are most frequently used for diagnosis. The experiment was conducted in a group of ten Kladrub mares. Six blood samples were taken from each of the mares within ten days. The measured values were subjected to statistical processing and repeatability coefficients (r op) were calculated. All the r op values were high (ALP--0.96, LD--0.93, ...
Diurnal changes in the metabolic indices in the blood of racing Arabian horses. In 8 stallions and 6 mares of pure Arabian breed the diurnal changes in the levels of lactic and pyruvic acid, glucose, and alkaline reserve were studied. All of them showed distinct diurnal changes but they failed to fulfil the criteria of circadian rhythm according to Halberg. It was found that all peaks occurred during the dark phase of the 24 h period except the glucose level in the stallions. Three of the indices studied showed higher mean diurnal levels in the mares than in the stallions. Only in the glucose level the mean values were reversed.
Active-site titration of horse urinary kallikrein. Horse urinary kallikrein was titrated with the reagent 4-nitrophenyl 4-guanidino-benzoate. The titration was shown to be dependent upon the concentration of the titrant. This finding, which distinguishes horse urinary kallikrein from other enzymes, is explained by the relatively small ratio between its rate of acylation and deacylation (k2/k3 = 16.8) and by a low affinity of the reagent (Km = 1.16 microM). By an appropriate kinetic treatment, it was possible to establish the relationship between the hydrolysis of 4-nitrophenyl 4-guanidinobenzoate and the actual concentration of the active enzy...
Effects of dietary supplementation with butylated hydroxyanisole, cysteine, and vitamins B on tansy ragwort (Senecio jacobaea) toxicosis in ponies. Dried tansy ragwort, which contains pyrrolizidine alkaloids, was fed as 10% of a complete diet to ponies, with and without a mixture of additives. The additives provided a dietary supplement equivalent to 1% cysteine, 0.75% butylated hydroxyanisole, 200 micrograms of vitamin B12/kg of feed, and 5 mg of folic acid/kg of feed. The additives did not alter tansy ragwort toxicity, as assessed by survival time, liver changes, sulfobromophthalein (BSP) clearance rate, serum gamma-glutamyl transpeptidase activity, and plasma amino acid patterns. In ponies fed tansy ragwort, BSP clearance rate was a se...
Predominantly beta-adrenergic control of equine sweating. Single equine sweat glands were found to secrete for more than 1 h in vitro in response to pharmacologic secretagogues. The adrenergic agonists epinephrine and norepinephrine evoked maximal sweat rates of 2.0 nl X gland-1 X min-1. However, the concentration of norepinephrine (10(-5) M) required to evoke the maximal response was 10 times higher than that for epinephrine. Maximal sweat rates also were stimulated with the beta 2-adrenergic agonist terbutaline. This stimulation was blocked by the beta-adrenergic antagonist propranolol. Moderate sweating responses were also obtained with the alpha-...
