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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.
Malignant hyperthermia-like reactions in three anesthetized horses. Problems encountered during halothane anesthesia in 3 horses included increasing rectal temperature, muscle rigidity or movement during anesthesia, irregular breathing patterns, and difficulty in stabilizing blood pressure. One horse had prolonged muscle fasciculations and failure to relax after administration of succinylcholine in addition to halothane. That horse developed severe, bilateral myositis of the triceps, lumbar, and gluteal muscles. Problems encountered were similar to those caused by the disease known as malignant hyperthermia.
The effects of stanozolol and boldenone undecylenate on scrotal width, testis weight, and sperm production in pony stallions. Fifty mature pony stallions were randomly assigned to one of five treatment groups: Group 1- controls (no treatment), Group 2 - 0.55 mg/kg stanozolol weekly for 13 treatments, Group 3 - 1.1 mg/kg stanozolol every 3 weeks for 5 treatments, Group 4 - 1.1 mg/kg boldenone undecylenate every 3 weeks for 5 treatments, and Group 5 - 0.55 mg/kg boldenone undecylenate weekly for 13 treatments. Scrotal widths (SW), combined testis weights (CTW), and daily sperm productions (DSP) were not different between Groups 1 and 2. Ponies in Group 5 had smaller SW (P<0.01), smaller CTW and decreased DSP compare...
Induced abortion with two prostaglandin F2 alpha analogues in mares: plasma progesterone changes. Three experiments were conducted to test the abortifacient effects of PGF2 alpha analogues on mares during midgestation (average gestation length 141.5 days). The progesterone concentration was measured by radioimmunoassay. In experiment 1. five mares received an injection of PGF2 alpha analogue (fluprostenol: 500 micrograms intramuscularly) and a second injection either at 24, 48, of 72 h. Although the progesterone concentration decreased (P less than 0.05) an average of 44 per cent in 24 h, none of the pregnancies were terminated. In experiment 2, beginning at least 10 days after experiment ...
Copper and zinc levels in the blood of thoroughbreds in training in the United Kingdom. The concentration of copper and zinc in the blood and sera of over 300 Thoroughbreds in training was determined by atomic absorption between February 1979 and July 1981. The mean (+/- sd) concentration of copper in the serum of stabled Thoroughbreds (79 +/- 16 micrograms/dl) was significantly (P less than 0.0001) lower than that of those at grass (101 +/- 26 micrograms/dl), whereas the mean serum zinc concentration of stabled Thoroughbreds (170 +/- 54 micrograms/dl) was higher than that of those at grass (111 +/- 45 micrograms/dl). No such differences were observed in whole blood. There were m...
Experimental studies of drug-induced impaction colic in the horse. Colic was induced in horses and ponies following topical or intravenous (iv) administration of amitraz, a formamidine acaricide. The condition was characterised by rapid cessation of intestinal sounds, stasis, extensive impaction and tympany throughout the large colon. Three animals that were necropsied had a faecalith obstructing the proximal small colon aboral to marked colonic impaction. A reproducible and reversible impaction colic syndrome could be induced by an iv injection of 1 mg amitraz/kg body weight in solvent. There were immediate central nervous system and intestinal signs. Large ...
Warfarin pharmacokinetics in the horse. The pharmacokinetics of racemic warfarin were studied in 6 adult horses. After IV administration, the plasma concentration of warfarin showed a biphasic decline in time. Analysis of the data, according to 2-compartment kinetics, revealed the following constants: biological half-life was 13.3 hours, apparent volume of distribution was 0.46 L X kg-1, body clearance was 25.3 ml X hour-1 X kg-1. Warfarin was bound (91.5%) to plasma proteins. Unchanged warfarin was not detected in the urine. Absorption from the gastrointestinal tract was almost complete. Concentrations of warfarin in tissue were ex...
Insulin tolerance in laminitic ponies. Sensitivity to insulin was assessed in ponies episodically affected with chronic laminitis by measurement of blood glucose and arterial blood pressure during insulin tolerance tests. In terms of blood glucose values, laminitic ponies were significantly less sensitive to insulin than controls. Conversely, a post-insulin decline in diastolic, systolic and mean blood pressure values was significantly greater in laminitic ponies than in controls.
Plasma cortisol and beta-endorphin in horses subjected to electro-acupuncture for cutaneous analgesia. Electro-acupuncture (EA) treatment of horses to induce cutaneous analgesia also increased plasma concentrations of beta-endorphin (beta-EP) and cortisol. The magnitude of these increases did not relate consistently to the degree of EA-induced analgesia. Respiration and heart rates were also markedly increased during EA treatment. Intact female horses had higher packed cell volume and plasma beta-EP as well as lower plasma total protein than castrated male horses. Plasma cortisol, heart rate, and respiration rate did not differ significantly between sexes. None of the parameters measured before...
Allergen-specific ELISA for horse IgE. An enzyme-linked immuno sorbent assay (ELISA) for measuring horse IgE specific to ovalbumin, bencylpenicilloic acid and odinitrocarboxyphenol is described. We used a sandwich type of ELISA by which horse serum was incubated in antigen-coated tubes containing one additional polystyrene ball, followed by rabbit anti horse IgE serum. The tubes were then incubated with biotinylated goat anti rabbit globulin followed by avidin coupled to phosphatase. Endpoint titrations were compared. The ELISA is highly reproducible due to the pretreatment of the polystyrene with glutaraldehyde. The increased anti...
[Study of conformational changes in alcohol dehydrogenase during its interaction with silochrome adsorbent by the EPR spectroscopy method]. The possible use of EPR spectroscopy (spin labelling) for the study of horse liver alcohol dehydrogenase with a silochrome adsorbent is discussed. The rotatory diffusion of nitroxyl labels chemically linked to the enzyme was studied with reference to the time of the enzyme incubation with the adsorbent and the degree of its accumulation on the adsorbent surface. The mobility of nitroxyl radicals attached to the protein globules was shown to increase with time. It was concluded that the conformation of the enzyme molecules changes during their interaction with the adsorbent.
Fatty acid composition of serum lipids in fasting ponies. Alterations in the fatty acid distribution of total lipid extracts and 4 of the major lipid subclasses of serum in ponies fasted overnight and for 4 and 7 days were determined. Although increases in 16:0, 16:1, and 18:3 omega 3 were observed, decreased amounts of 18:0 and 18:2 omega 6 combined to cause no significant change in the saturated to unsaturated fatty acid ratio in the total extracts. Phospholipid became somewhat preferentially enriched in saturated fatty acids due to a decrease in 18:1, although this response was variable. The free fatty acid and triglyceride fractions both showed i...
Influence of acepromazine maleate on the equine haematocrit. The effect of acepromazine maleate (ACP) on the equine venous haematocrit and total plasma protein concentration was studied in six clinically normal horses. Total plasma protein concentration was not appreciably influenced by ACP. However, the haematocrit decreased with the duration, but not the degree, of the decrease being dose-related. Mean haematocrit values returned to control levels by 12 h after 0.05 mg ACP/kg body weight and 21 h after 0.15 mg ACP/kg body weight.
Measurement of tracheal mucous transport rate in the horse. Tracheal mucous transport rates were measured in 12 nonanesthetized horses after an intratracheal injection of 99mtechnetium-sulfur colloid. The transport rate of the subsequent bolus of radioactivity was determined, using a portable scaler rate meter fitted with a high-energy gamma-scintillation probe. A gamma-scintillation camera was used to verify bolus form and movement in 1 horse. The mean tracheal mucous transport rate was 1.66 +/- 0.24 cm/min.
Studies on the physiopathology of chronic obstructive pulmonary disease in the horse. VIII. Mean modal vectors of the P wave and the QRS complex. Mean modal vectors of P1, P2 and QRS were determined in the 3 planes of a semi-orthogonal EKG lead system in 17 horses and ponies with chronic obstructive pulmonary disease (COPD) and in 17 clinically normal horses and ponies. Subjects were paired so that the heart rates of each pair were not dissimilar by more than 2 cycles per minute. Probably significant differences were observed between the mean angles of P1 vectors in the transverse and sagittal planes (T plane, normal = 324 degrees +/- 24,6 degrees, COPD = 342 degrees +/- 21,0 degrees, t = 2,0, P less than 0,05; S plane, normal = 331 deg...
Chemiluminescence response of equine alveolar macrophages during stimulation with latex beads, or IgG-opsonized sheep red blood cells. Isolated equine alveolar macrophages were shown to generate a luminol-dependent light response when challenged with a phagocytic stimulus. The chemiluminescent response was not detected with luminol prepared at 1.0 x 10(-5) or 1.0 x 10(-4) molar concentrations, but was readily quantitated when used at a 1.0 x 10(-3) molar concentration. Challenge of the alveolar macrophages with latex particles or with equine IgG-coated sheep red blood cells elicited the luminol-dependent light response, whereas unchallenged equine alveolar macrophages or those challenged with unopsonized erythrocytes failed t...
Aggregation of equine platelets by PAF (platelet-activating factor). Platelet-activating factor (PAF), a lipid released as a result of immediate allergic reactions from basophils and mast cells as well as by a variety of other cell types and stimuli, is one of the most potent platelet agonists and hypotensive agents known. Equine platelets stimulated over a wide range of PAF concentrations aggregated in a time- and dose-dependent manner. Maximum aggregation was observed at concentrations of PAF as low as 3.58 x 10(-14) M with platelet-rich plasma (PRP) and 3.58 x 10(-16) M with washed platelets. Furthermore, the aggregation observed did not appear to be breed-d...
Transmural coronary vasodilator reserve and flow distribution during severe exercise in ponies. Transmural distribution of myocardial blood flow and coronary vasodilator reserve (15-microns-diam radionuclide-labeled microspheres) was studied in 11 adult, healthy ponies at rest and during moderate and severe exercise performed on a treadmill (heart rate 56 +/- 4, 154 +/- 3, and 225 +/- 7 beats . min-1, respectively.). Exercise resulted in a marked increase in cardiac output, mean aortic pressure, right ventricular (RV) systolic and end-diastolic pressure, left ventricular (LV) end-diastolic pressure, and the maximum rate of rise of LV pressure LV (dP/dtmax). Accompanying these changes was...
Heritability and repeatability of speed for 2- and 3-year-old standardbred racehorses. Repeatabilities (t) and heritabilities (h2) of racing time were estimated from data on 7,206 2- and 3-yr-old Standardbred pacers and trotters competing in 1-mile (1.6 km) charted races at six tracks between 1975 and 1978. A total of 38,487 records representing 2,387 sire progeny groups were divided into subsets by gait, age and track. Initially, the designation "class of race" was recognized as a subjective categorization that reflected nonrandom assignments of horses to races. After extensive investigation, we concluded that racing times should be adjusted by linear regression for the time of...
Effect of ambient temperature upon the surface temperature of the equine limb. Ten clinically healthy adult horses were examined with the portable infrared thermometer at ambient temperatures of 5, 15, and 25 C to evaluate the thermal response of limbs of the horse to variations of ambient temperature. Limb surface temperature varied in direct proportion to changes in the ambient temperature, with considerable variation occurring among individual horses, especially at the lower temperatures. Areas of proximal parts of the limbs were more resistant to temperature variation than were distal parts. Ambient temperature had a statistically significant, but clinically unimport...
Surface receptors for IgG and complement on equine alveolar macrophages. Isolated equine alveolar macrophages obtained by bronchopulmonary lavage of four live ponies demonstrated surface receptors for equine IgG, equine IgM, and complement-coated sheep red blood cells, but not equine IgM or complement-coated erythrocytes alone. In addition, demonstration of IgG receptors was found to depend on the level of erythrocyte sensitization and could not be demonstrated by red blood cell rosetting techniques at low levels of sensitization. Demonstration of receptors for equine complement by red cell rosetting techniques required the presence of both IgM antibody and serum d...
Automatic noninvasive sphygmomanometry in horses. Systolic, diastolic, and mean arterial blood pressures and heart rate were determined in 73 horses, using an indirect automatic oscillometric technique. Blood pressure and heart rate data obtained by sphygmomanometry were compared with similar data obtained from cannulation of the horses' facial or dorsal metatarsal arteries. Good correlation between direct (actual) and indirect (oscillometric) blood pressures and heart rate measurements were obtained when the heart rate was low, using high sensitivity setting. Cardiac arrhythmias or hypotension prevented oscillometric measurements from being ...
Pharmacokinetics of phenytoin (diphenylhydantoin) in horses. The pharmacokinetics of the anti-convulsant phenytoin were investigated in clinically healthy horses after oral (p.o.) and intravenous (i.v.) administration. A single dose of phenytoin (8.8 mg/kg body weight) was given i.v. as a bolus to nine horses and one horse received 13.2 mg/kg. A two-compartment open model was used to describe the disposition of phenytoin. Four of the horses that received an i.v. dose (three at 8.8 mg/kg and one at 13.2 mg/kg) were then given the same dose 3 days later by the oral route. Phenytoin achieved a peak concentration in serum within 1-4 h after p.o. administrat...
[The value of blood progesterone determination about 18 days post ovulation for pregnancy testing in mares]. The reliability of determination of the plasma progesterone level within approximately eighteen days after ovulation in the pregnancy diagnosis of mares is examined in the present study. Studies were done in seventy-five mares, a number of which were served or inseminated during several cycles so that a total number of eighty-seven blood samples were obtained. On the analogy of other authors, the progesterone level above which mares were believed to be pregnant and below which they were assumed to be non-pregnant, was set at 2 ng/ml. The twenty-five mares in which the level was below 2 ng/ml. ...
Localization of the second calcium ion binding site in porcine and equine phospholipase A2. At alkaline pH porcine pancreatic phospholipase A2 is known to bind two Ca2+ ions per protein molecule. One Ca2+ ion is strongly bound to the active site and is essential for enzyme activity. A second Ca2+ ion binds more weakly to the protein and improves the affinity of the enzyme for lipid-water interfaces severalfold at high pH values. A group having a pK around 6 controls enzyme binding to lipid-water interfaces in the absence of Ca2+. By use of proton titration techniques this group is now identified to be a carboxylate having an abnormally high pK. Its pK shifts to a value around 4.5 in ...
An in vitro study on joint fitting and cartilage thickness in the radiocarpal joint of foals. The change in the degree of fitting of the opposing articular cartilage surfaces of the radiocarpal joint of foals was studied in vitro using a pneumatic loading device. The thickness of the articular cartilage of the distal radius was examined using radiographic and histological techniques. The thickest cartilage corresponded with the approximate centre of the contact area of the opposing articular surface. The variations in articular cartilage contact area and thickness are discussed.
