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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.
Quantitative determination of equine alkaline phosphatase isoenzymes in foal and adult serum. Automated and semiautomated assays were developed and validated for the determination of equine alkaline phosphatase isoenzymes including intestinal (IALP), bone (BALP), and liver (LALP). The addition of levamisole selectively inhibited more than 97% of LALP while inhibiting only 55% of IALP. Because these percentages were highly reproducible in an automated system, the IALP activity could be calculated in a sample. Bone alkaline phosphatase isoenzyme was selectively precipitated by adding an equal volume of wheat germ agglutinin (5 mg/mL), incubating for 30 minutes at 37 degrees C, and centri...
Nutrient utilisation by the hindlimb of thoroughbred horses at rest. Nutrient uptake by the hindlimb was investigated utilising the arteriovenous difference technique in 5 Thoroughbred horses fed to maintenance a diet of 100% roughage or 52% oat grain and 48% roughage. Arterial blood was obtained from a catheter inserted into the carotid artery while venous blood was simultaneously collected from a catheter placed into the iliac vein via the medial saphenous vein. The arteriovenous difference for glucose was significant and represented a mean extraction of 10 +/- 1% with no effect of diet. If fully oxidised, glucose uptake (corrected for lactate and pyruvate ar...
Quantification of the locomotion of Dutch Warmblood foals. To get an in-depth insight into the ontogeny of the equine locomotor apparatus, the locomotion of 28 Dutch Warmblood foals was recorded at the walk, trot and canter on a treadmill using a CODA-3 apparatus. A great similarity in joint angle-time diagrams was found, although considerable differences in kinematic gait parameters of individual foals could be detected. These results contribute to an objective comparison of the locomotor performance of foals.
The correlation of running ability and physiological variables in thoroughbred racehorses. The running abilities of 25 Thoroughbred racehorses were measured at distances of 1200, 1600 and 20000 m. Various physiological variables were measured subsequently on the treadmill and correlated with running speed. There was a negative correlation for running speed with the velocity (VLa4) and work rate (WLa4) at which blood lactate reaches a steady-state concentration of 4 mmol/litre and a positive correlation with peak plasma lactate, suggesting that plasma lactate concentrations of faster horses rise more rapidly and to higher levels than do those of slower horses. The correlation between...
Serum triiodothyronine, total thyroxine, and free thyroxine concentrations in horses. The objectives of this experiment were to determine serum concentrations of triiodothyronine (T3), thyroxine (T4), and free thyroxine (fT4) at rest, following thyroid-stimulating hormone (TSH) administration, and following phenylbutazone administration in healthy horses. This was done to determine which available laboratory test can best be used for diagnosis of hypothyroid conditions in horses. Serum T3, T4, and fT4 concentrations in serum samples obtained before and after TSH stimulation and following phenylbutazone administration for 7 days were determined. Baseline values ranged from 0.21 ...
The effect of starting time on dexamethasone suppression test results in horses. This study was conducted to investigate the effect of starting time on dexamethasone suppression test results in horses. Eight adult horses were used throughout the trial. Baseline cortisol levels were established by collecting cortisol levels twice daily, at 8:00 A.M. and 8:00 P.M. for 4 consecutive days. Morning baseline cortisol levels were 46.3 +/- 5.94 ng/ml, and evening baseline cortisol levels were 32.8 +/- 5.59 ng/ml. Although lower, the evening cortisol levels were not statistically different (P = 0.154) from the morning levels. Dexamethasone suppression tests initiated at either 9:00...
Further observations on the morphology and sensitive innervation of the retractor penis muscle in several species of ungulates. The retractor penis muscle originates from the vertebrae in pigs, horses, cattle and goats; it arises from the rectum in sheep. In all the species considered, sensitive innervation was found. This was represented by encapsulated receptors. Nervous vegetative supply, made up of isolated or assembled ganglion cells, was also present. Among the numerous sensory nerve endings found in pigs, goats and sheep were Pacinian, Pacinian-like, Golgi-Mazzoni corpuscles and Krause's end bulbs (genital corpuscles). Few Pacinian and Pacinian-like corpuscles were found in cattle and horses. A hypothesis on the...
Intraosseous pressure and pathologic changes in horses with navicular disease. Navicular bone intraosseous pressure, gross pathologic, histologic, and histochemical data were collected from 8 horses with navicular disease and 4 control horses. Simultaneous navicular bone intraosseous, medial palmar arterial, and saphenous venous pressures were measured for the left and right forelimbs of each horse under general anesthesia. Gross pathologic evaluation included grading of changes on the flexor surface of the navicular bone. Safranin-O-fast green-stained sections were used for histologic-histochemical grading of the hyaline articular and fibrocartilage surfaces of the navi...
Clinical biochemical determinations in the Mangalarga-Paulista horse: reference values. Biochemical values are widely related with environmental agents, sex and age, and are used in disease diagnosis. Numerous reports have been published on the biochemical parameters of different breeds of horses. However, there is a paucity of information concerning Cu-Zn superoxide dismutase (SOD), ceruloplasmin, copper and zinc determinations in the serum. Blood samples from a total of 60 horses of the Mangalarga-Paulista breed, representing three age groups (0 to 4 months old, 6 to 18 months old and adult) were examined. Male horses have a higher mean value of SOD, ceruloplasmin and copper th...
A comparison of the traditional Chinese versus transpositional zangfu organ association acupoint locations in the horse. The traditional Chinese (TC) and transpositional (TP) methods of animal acupoint location result in different acupoint charts. Representative TC and TP equine zangfu organ shu-association acupoint charts are compared to each other and to a human chart. Despite their differences, practitioners of both methods appear to achieve equally effective therapeutic results--a phenomenon termed "traditional Chinese/transpositional equal efficacy" (TTEE). Common veterinary acupuncture practices, traditional Chinese medical theory, spinal cord anatomy, and a preliminary equine "association segment" chart a...
Kinetic analysis of D-xylose distribution after intravenous administration to mares. Multicompartmental analysis was applied to study the kinetics of D-xylose distribution after IV administration to healthy mares deprived of food for 12 and 96 hours. Urinary excretion of D-xylose was measured over a 15-hour period after administration. The plasma D-xylose concentrations in this study were in the range found after oral tolerance testing. The disposition of D-xylose was described by a two-compartment model with linear kinetic characteristics. Total volume of distribution decreased significantly (P < 0.025) from 0.270 L/kg of body weight after the 12-hour period of food depriv...
High density lipoprotein metabolism in the horse (Equus caballus). 1. Apolipoprotein A-I dependent lecithin:cholesterol acyl transferase (LCAT) activity was identified in equine lipoprotein deficient plasma (LPDP). 2. LCAT activity showed no breed or sex variation, and was unaltered postprandially. 3. There was no significant cholesteryl ester transfer activity in equine LPDP. 4. Hydrophobic interaction chromatography on phenyl sepharose failed to unmask transfer activity or identify an inhibitor of cholesteryl ester transfer. 5. In 12 Shetland ponies, plasma high density lipoprotein (HDL) concentrations were positively correlated with those of triglyceride, ...
Equine fasting hyperbilirubinemia. It appears that different mechanisms responsible for fasting hyperbilirubinemia may be operative in different mammalian species (and subspecies). An increase in bilirubin production does not seem to occur in the horse, but a decrease in the hepatic uptake of bilirubin has been supported by a number of studies. Even though the delay in plasma elimination could also result from a decrease in hepatic blood flow, this possibility does not seem to play a major role since the hepatic uptake of compounds with low intrinsic hepatic clearance (e.g., ICG and bilirubin) appear to be affected more during ...
A method to estimate the initial length of equine tendons. A procedure is described by which the length of a tendon at the onset of loading is determined objectively. The procedure includes the fitting of third-order polynomial functions on the load-elongation data. The onset of loading is detected by an increasing fit of the polynomial by selective data reduction of the initial part of the load-elongation curve. The procedure results in an objective and reproducible definition of the zero strain level of a tendon.
Immunochemical studies of equine chorionic gonadotropin (eCG), eCG alpha, and eCG beta. The equine (e) placental glycoprotein hormone eCG plays a critical though not completely understood role during the first trimester of gestation in mares. In the present work, we have developed immunoradiometric assays (m-IRMAs) for detection of eCG, eCG alpha, and eCG beta using combinations of monoclonal antibodies (mAbs) specific for epitopes that reside on free and/or combined subunits. The free eCG alpha m-IRMA was based on AHT20 mAb, specific for the free alpha-subunit of all species, and 125I-labeled ECG01 mAb, which recognizes both free and combined alpha-subunit from equine and primat...
Strain of the musculus interosseus medius and its rami extensorii in the horse, deduced from in vivo kinematics. The in vivo strains of the musculus interosseus medius (suspensory ligament) and its rami extensorii (extensor branches) in the forelimb of the horse were determined from angular changes of the metacarpophalangeal and the distal interphalangeal joints. For this purpose, regression models were fitted to strains and joint angle combinations measured in in vitro limb loading experiments. The in vivo strains were computed from the kinematics of 8 horses at the walk, the trot and the canter. It was found that the extensor branches were strained about 1.0% at hoof impact, which indicates that they p...
Lipids and calcium uptake of sperm in relation to cold shock and preservation: a review. When sperm of the ram, bull, boar and stallion are cold-shocked by rapid cooling to near freezing point, motility and metabolic activity are irreversibly depressed and the acrosome and plasma membrane disrupted. Ram sperm become susceptible to cold shock in the proximal corpus region of the epididymis when the cytoplasmic droplet has moved backwards to the distal portion of the sperm midpiece. The membrane constituents phospholipids and cholesterol are important in cold shock which causes loss of lipid from sperm. The susceptibility of sperm to cold shock is linked with a high ratio of unsatur...
Turbidity of hyperimmune equine antivenom: the role of phenol and serum lipoproteins. Twenty batches of polyvalent antivenom produced at the Instituto Clodomiro Picado were analyzed for turbidity, both before and after freezing-thawing and lyophilization. Eight batches became turbid upon freezing-thawing, and this change correlated with high levels of cholesterol, triglycerides and lipoproteins, especially beta-lipoprotein. Since normal horse serum does not become turbid after freezing-thawing, despite the fact that it has high lipoprotein levels, the possibility was raised that phenol, used as a preservative during serum fractionation, might affect lipoproteins, inducing the a...
Complexoproductive and antiheparin properties of low density lipoproteins (LDL). VI. Antiheparin activity in blood plasma of different species of vertebrates. Antiheparin activity of plasma of different species of vertebrates depends to a large extent on contents of low density lipoproteins (LDL). High antiheparin activity of the blood plasma of chicken and human corresponds to high contents of LDL and low antiheparin activity of the blood plasma of horse, cow, sheep, dog and pig corresponds to decreased contents of these proteins. Differences in the contents of fibrinogen, acid alfa1-glycoproteins, globulins, alkaline proteins and antithrombin III activity have smaller influence on antiheparin activity in the blood plasma of the examined animals.
Concept of a force-measuring horseshoe. To further develop objective methods in the field of gait analysis a force-measuring horseshoe (FM shoe) has been developed. The ground reaction forces were determined by measuring the degree of displacement between the two solid parts of the shoe. This was done by three removable measuring units (MUs) that were equipped with strain gauges and placed in the toe and in each of the quarter parts. Before performing force recordings the sensors were calibrated with the actual MUs mounted on the shoe. This can be done in the field with a specially developed equipment. The shape of the signal genera...
Neurones in autonomic ganglia of normal horses contain phosphorylated neurofilaments. Neurofilaments (NF) are composed of three polypeptides of differing molecular size, termed NF-L, NF-M and NF-H. The NF-H and, to a lesser degree, NF-M components are phosphorylated. In the majority of normal neurones, the location of phosphorylated NF is confined to neuronal processes, particularly the axon, and excluded from the perikaryon. Cell bodies of autonomic neurones of the rat do not contain phosphorylated NF. In many disease states, phosphorylated NF accumulate in the neuronal cell body and therefore in most circumstances their presence indicates abnormality. This paper reports that ...
Species difference in modulation of calcium release by Naja naja kaouthia snake venom cardiotoxin in terminal cisternae from human and equine skeletal muscle. The modulation of Ca2+ release by a cardiotoxin (CTX) from Naja naja kaouthia snake venom was examined in terminal cisternae-containing fractions from equine and human skeletal muscle. Pretreatment with CTX (10 microM) decreased by 27% (human muscle), or had no effect on (equine muscle), the threshold of Ca(2+)-induced Ca2+ release. If terminal cisternae fractions were first preloaded with Ca2+ to greater than 65% of the threshold of Ca(2+)-induced Ca2+ release and then CTX added, an immediate and sustained release of Ca2+ occurred in preparations from both species. Addition of CTX after a Ca2...
Changes in cross-sectional area and capillary supply of the muscle fiber population in equine gluteus medius muscle as a function of sampling depth. The right and left gluteus medius muscles of 4 mature Andalusian stallions were examined by repeated needle biopsy over a specific area and depth, as well as at different depths, to determine whether the cross-sectional area and capillary supply of the various fiber types are homogeneous throughout the muscle. The muscle biopsy specimens were histochemically analyzed for fiber types (myofibrillar adenosine triphosphatase) and capillaries (amylase-periodic acid-Schiff method). Differences between contralateral sites were not identifiable for any of the analyzed variables. Differences between sa...
Insulin-like growth factor binding proteins of equine serum. Ligand blotting analysis of serum from the horse using radiolabelled IGF-I revealed a protein at 96 kDa which was not present in serum from goat, cow, sheep, deer or donkey. These latter species all displayed five labelled bands in the range 24 to 41 kDa. Conversely, these were only weakly labelled in serum from the horse. Size exclusion chromatography of horse serum pre-incubated with radiolabelled IGF-I revealed reduced binding in the 130-kDa peak compared with goat plasma, and ligand blotting analysis indicated the 96-kDa protein was present in this peak. The 96-kDa protein from horse serum...
Crystal structure of a complex between electron transfer partners, cytochrome c peroxidase and cytochrome c. The crystal structure of a 1:1 complex between yeast cytochrome c peroxidase and yeast iso-1-cytochrome c was determined at 2.3 A resolution. This structure reveals a possible electron transfer pathway unlike any previously proposed for this extensively studied redox pair. The shortest straight line between the two hemes closely follows the peroxidase backbone chain of residues Ala194, Ala193, Gly192, and finally Trp191, the indole ring of which is perpendicular to, and in van der Waals contact with, the peroxidase heme. The crystal structure at 2.8 A of a complex between yeast cytochrome c pe...
[Prenatal development of the horse ovary]. To answer the many open questions concerning the development of the horse's ovary, first the prenatal development was investigated. It resulted that follicles derive from the germinal epithelium and its cords, whereas the Leydig cells and the rete blastema originate from the mesonephros. In the second third of pregnancy the Leydig cells undergo an enormous proliferation, in the last third they degenerate. However this degeneration is not connected with the postnatal development of the ovulation groove.
Equine vision and optics. Vision is a marvelous sense, critical to the well-being and functional use of horses. Anatomic, optical, and visual acuity generalities are presented. The constituents of unsoundness due to equine ocular disease are discussed, and recommendations are made.
Clinical assessment of selenium status of livestock. Assessment of the selenium status of livestock is an important aspect of production medicine, but variations in reported values between laboratories and between methods may be > 30%. Reliable interpretations require considerable experience with an assay and an extensive database from field and research case samples of a variety of species. The Michigan State University Animal Health Diagnostic Laboratory (MSU-ADHL) has offered Se analyses by acid-digestion and fluorometric detection since 1982. This laboratory expects serum Se values (nanograms per milliliter) of livestock to increase graduall...
Visual acuity in the horse. We assessed the ease with which horses could learn visual discriminations and measured their resolution acuity. We trained three horses to press their noses against one of two large wooden panels to receive a small food reward. Following training on a series of two-choice discrimination tasks, resolution acuity was measured. Although there was some variability between animals, the best acuity obtained was 23.3 c deg-1. Within the margin of error imposed by limited anatomical data, the obtained values are consistent with predictions based on retinal ganglion cell density estimates and posterior...
Specialized veins in the submucosa of the equine ileocecal junction. Spirally arranged bundles of sub-endothelial smooth muscle enfold the small to medium-sized submucosal veins in the equine ileocecal junction. The muscle bundles, accompanied by the endothelial lining, bulge into the lumen of the vessels, partly occluding the latter. Transmission electron microscopy of the muscle cells reveals features consistent with vascular smooth muscle ultrastructure. It is proposed that the throttling effect of the muscle bundles causes engorgement of the submucosal venous plexus, which then assists in the closing of the ileocecal orifice.
