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Topic:Muscle
The topic of muscle in horses encompasses the study of equine muscle structure, function, and physiology. Muscles in horses are responsible for movement, posture, and various metabolic processes. They are composed of muscle fibers that contract and relax to produce motion and generate force. Research in this area often focuses on muscle development, adaptation to exercise, and the impact of nutrition and training on muscle performance. Conditions such as muscle fatigue, injury, and disorders like equine exertional rhabdomyolysis are also explored. This page compiles peer-reviewed research studies and scholarly articles that investigate the anatomy, physiology, and clinical aspects of muscle in equine species.
In vivo muscle function vs speed. II. Muscle function trotting up an incline. Different locomotor tasks, such as moving up or down grades or changing speed, require that muscles adjust the amount of work they perform to raise or lower, accelerate or decelerate the animal's center of mass. During level trotting in the horse, the triceps had shortening strains of around 10.6% while the vastus shortened 8.1% during the stance phase. Because of the 250% increase in metabolic rate in horses trotting up a 10% incline which is, presumably, a result of the increased requirement for mechanical work, we hypothesized that muscle strain during trotting would be increased in both th...
In vivo muscle function vs speed. I. Muscle strain in relation to length change of the muscle-tendon unit. The activity of muscles can be concentric (shortening), eccentric (lengthening) or isometric (constant length). When studying muscle function it is important to know what the muscle fascicles are actually doing because the performance of muscle is strongly influenced by the type of activity: force decreases as a function of shortening velocity during concentric contractions; force produced during eccentric contractions can be stronger than maximum isometric force, and force production is enhanced if a concentric contraction follows an eccentric phase. It is well known that length changes of mu...
Muscle metabolic changes associated with long-term inhalation anaesthesia in the horse analysed by muscle biopsy and microdialysis techniques. During anaesthesia in the horse, muscle blood flow has been found to be reduced, possibly leading to hypoxia or ischaemia in the muscle. The aim of this study was to use the muscle biopsy and microdialysis techniques to determine whether long-term inhalation anaesthesia in laterally recumbent horses induces metabolic changes in gluteal muscle indicative of anaerobic metabolism. Muscle biopsies and plasma samples were taken from seven horses at the start and end of halothane anaesthesia. In six isoflurane-anaesthetised horses, given three pharmacological provocations (dobutamine, detomidine, ac...
The role of the extrinsic thoracic limb muscles in equine locomotion. Muscles have two major roles in locomotion: to generate force and to absorb/generate power (do work). Economical force generation is achieved by short-fibred pennate muscle while the maximum power output of a muscle is architecture independent. In this study we tested the hypothesis that there is an anatomical and structural separation between the force-generating anti-gravity muscles and the propulsive (limb/trunk moving) muscles of the equine forelimb. Muscle mass and fascicle length measurements were made on the thoracic limb extrinsic muscles of six fresh horse cadavers. Physiological cros...
Aerobic training, but not creatine supplementation, alters the gluteus medius muscle. The aim of the present study was to investigate the effect of oral supplementation of creatine on the muscular responses to aerobic training. Twelve purebred Arabian horses were submitted to aerobic training for 90 d, with and without creatine supplementation, and evaluated with respect to BW and BCS and to the area and frequency of the different types of muscle fibers in the gluteus medius. Supplementation consisted of the daily administration of 75 g of creatine monohydrate mixed into the ration for the 90 d of training. Physical conditioning was conducted on a high-performance treadmill, an...
Systemic AL amyloidosis associated with multiple myeloma in a horse. AL amyloidosis is the most common type of systemic amyloidosis in humans, and it is frequently associated with multiple myeloma. But, AL amyloidosis is very rare in domestic animals. A 16-year-old Quarter horse gelding was diagnosed with systemic AL amyloidosis associated with multiple myeloma. Clinical problems were rapid weight loss, muscle atrophy, soft unformed stool, and ventral edema. Grossly, diffuse gastrointestinal hemorrhage, markedly thickened jejunal mucosa, and splenomegaly were present. Microscopically, diffuse severe amyloid deposits were present in the lamina propria of glandul...
Passive and active mechanical properties of the superficial and deep digital flexor muscles in the forelimbs of anesthetized Thoroughbred horses. The superficial (SDF) and deep digital flexor (DDF) muscles are critical for equine forelimb locomotion. Knowledge of their mechanical properties will enhance our understanding of limb biomechanics. Muscle contractile properties derived from architectural-based algorithms may overestimate real forces and underestimate shortening capacity because of simplistic assumptions regarding muscle architecture. Therefore, passive and active (=total - passive) force-length properties of the SDF and DDF muscles were measured directly in vivo. Muscles from the right forelimbs of four Thoroughbred horses we...
The effect of varying dietary starch and fat content on serum creatine kinase activity and substrate availability in equine polysaccharide storage myopathy. The effect of dietary starch and fat content on serum creatine kinase (CK) activity and substrate availability was evaluated in 4 mares of Quarter Horse-related breeds with polysaccharide storage myopathy (PSSM). Four isocaloric diets ranging in digestible energy (DE) from 21.2% (diet A), 14.8% (B), 8.4% (C), to 3.9% (D) for starch, and 7.2% DE (diet A), 9.9% (B), to 12.7% DE (diet C and D) for fat were fed for 6-week periods (4 weeks with exercise) using a 4 X 4 Latin square design. Postprandial glucose and insulin responses were measured, and 4 hours postexercise, serum CK activity, glucose,...
Sarcoplasmic masses in equine skeletal muscle. Sarcoplasmic masses in humans have been associated with various myopathies, although the significance remains elusive. Similar structures have also been observed in equine muscle. The aim of this study was to determine the frequency of such structures in normal and abnormal equine muscle, and to characterize these structures using histological, histochemical, immunohistochemical, ultrastructural, and morphometric analyses. The histological and histochemical appearance was similar to that of human sarcoplasmic masses with a central or subsarcolemmal distribution. Of interest was a predilection ...
The role of the extrinsic thoracic limb muscles in equine locomotion. Muscles have two major roles in locomotion: to generate force and to absorb/generate power (do work). Economical force generation is achieved by short-fibred pennate muscle while the maximum power output of a muscle is architecture independent. In this study we tested the hypothesis that there is an anatomical and structural separation between the force-generating anti-gravity muscles and the propulsive (limb/trunk moving) muscles of the equine forelimb. Muscle mass and fascicle length measurements were made on the thoracic limb extrinsic muscles of six fresh horse cadavers. Physiological cros...
New insights into the skeletal muscle phenotype of equine motor neuron disease: a quantitative approach. Equine motor neuron disease (EMND) is a neurodegenerative disorder similar to the sporadic form of human amyotrophic lateral sclerosis. This study was conducted to quantify myofiber plasticity in response to EMND. Deep M. gluteus medius biopsy samples from eight horses with an ante mortem diagnosis of EMND, which in five cases was later confirmed by post mortem examination of spinal cord and peripheral nerves, were examined by combined methodologies of electrophoresis of myosin heavy chains (MyHC), muscle enzymes and substrate biochemistry, immunohistochemistry of MyHCs and sarcoendoplasmic Ca...
Myonecrosis and cutaneous infarction associated with Salmonella serovar Infantum infection in a horse. A 5-year-old Quarter Horse mare was referred for evaluation of oral ulcers, limb edema, weight loss, and weakness. There was marked diffuse swelling extending from the stifle region to the tarsal region of the left hind limb, and the horse had a left hind limb lameness. Firm swellings ranging from 2 to 15 cm in diameter and consisting of nodules, plaques, and discrete masses were palpated on both sides of the neck, over the right shoulder region, over the left elbow region, and over the left caudoventral aspect of the abdomen. Laboratory abnormalities included hypoproteinemia, neutrophilia, an...
Exercise training increases oxidative capacity and attenuates exercise-induced ultrastructural damage in skeletal muscle of aged horses. Exercise training improves functional capacity in aged individuals. Whether such training reduces the severity of exercise-induced muscle damage is unknown. The purpose of the present study was to determine the effect of 10 wk of treadmill exercise training on skeletal muscle oxidative capacity and exercise-induced ultrastructural damage in six aged female Quarter horses (>23 yr of age). The magnitude of ultrastructural muscle damage induced by an incremental exercise test before and after training was determined by electron microscopic examination of samples of triceps, semimembranosus, an...
Insulin sensitivity and skeletal muscle glucose transport in horses with equine polysaccharide storage myopathy. Equine polysaccharide storage myopathy (PSSM) is an inherited disorder characterized by the accumulation of glycogen and abnormal polysaccharide in muscle with normal glyco(geno)lytic enzyme activities. The purpose of this study was to evaluate in vivo insulin sensitivity and glucose excursion in PSSM using a euglycemic hyperinsulinemic clamp. In addition, the content of muscle glucose transporters (GLUT1 and GLUT4) and the insulin receptor was determined in muscle biopsies using Western blot analysis. The glycogen content was 1.8-fold higher, and isolated polysaccharide analyzed by iodine abs...
Outcome of equids with clinical signs of West Nile virus infection and factors associated with death. To determine outcome of equids in the western United States with clinical signs of West Nile virus (WNV) infection and identify factors associated with risk of death in infected equids. Methods: Cross-sectional study. Methods: 484 equids in Nebraska and Colorado. Methods: Owners of 484 equids with laboratory-confirmed West Nile virus infection in Nebraska and Colorado were contacted by telephone, and a questionnaire was used to obtain information on signalment, management, clinical signs, date of disease onset, duration of disease, WNV vaccination status, and health status at the time of the i...
Effects of feeding meals with various soluble-carbohydrate content on muscle glycogen synthesis after exercise in horses. To determine effects of feeding diets with various soluble-carbohydrate (CHO) content on rates of muscle glycogen synthesis after exercise in horses. Methods: 7 fit horses. Methods: In a 3-way crossover study, horses received each of 3 isocaloric diets (a high soluble CHO [HC] diet, a low soluble CHO [LC] diet, or a mixed soluble CHO [MC] diet). For each diet, horses were subjected to glycogen-depleting exercise, followed by feeding of the HC, LC, or MC diet at 8-hour intervals for 72 hours. Results: Feeding the HC diet resulted in a significantly higher glycemic response for 72 hours and sign...
Exercise-induced oxidative stress and muscle stress protein responses in trotters. Acute exercise induces oxidative stress and heat shock protein (HSP) expression. Information on the protection of stress proteins against oxidant insult and muscle damage during moderate exercise is scanty. We aimed to show how a single bout of moderate exercise affects the markers of oxidative stress and heat shock factor-1 (HSF1; the transcriptional regulator of HSP synthesis), and HSP70, HSP90 and glucose-regulated protein (GRP75) expression in horses. Eight clinically normal and regularly trained standardbred trotters were treadmill-exercised for 45 min at moderate intensity. Blood samples...
Determination of muscle architecture and fiber characteristics of the superficial and deep digital flexor muscles in the forelimbs of adult horses. To provide a quantitative description of the architecture of superficial digital flexor (SDF) and deep digital flexor (DDF) muscles in adult horses to predict muscle-tendon behavior and estimate muscle forces. Methods: 7 forelimb specimens from 7 adult Thoroughbreds. Methods: Muscle and tendon lengths and volumes were measured from 6 fixed forelimbs. After processing, fiber bundle and sarcomere lengths were measured. Optimal fascicle lengths and muscle length-to-fascicle length, muscle length-to-free tendon length, and fascicle length-to-tendon length ratios were calculated, as were tendon and...
Gracilis muscle injury as a cause of lameness in two horses. Injury to the gracilis muscle can cause acute, severe lameness in horses. Two female Quarter Horses that were used for barrel racing sustained gracilis muscle tear injuries. The site of injury was localized by direct infiltration of the area with mepivacaine. The extent of muscle tearing and seroma formation was determined via ultrasonographic evaluation. One horse developed fibrotic myopathy approximately 3 months after the original injury and underwent surgery to transect a palpable fibrous band at the previous injury site. Both horses returned to barrel racing 5 to 6 months after the injury...
Molecular characterization and mutational screening of the PRKAG3 gene in the horse. The PRKAG3 gene encodes a muscle-specific isoform of the regulatory gamma subunit of AMP-activated protein kinase (AMPK). A major part of the coding PRKAG3 sequence was isolated from horse muscle cDNA using reverse-transcriptase (RT)-PCR analysis. Horse-specific primers were used to amplify genomic fragments containing 12 exons. Comparative sequence analysis of horse, pig, mouse, human, Fugu, and zebrafish was performed to establish the exon/intron organization of horse PRKAG3 and to study the homology among different isoforms of AMPK gamma genes in vertebrates. The results showed conclusively...
Transcranial magnetic stimulation: normal values of magnetic motor evoked potentials in 84 normal horses and influence of height, weight, age and sex. Cervical spinal cord dysfunction is a common problem in equine medicine and the currently available tests give no objective information about the functionality of the nervous tracts. Therefore, transcranial magnetic stimulation (TMS) was performed in 84 healthy horses of different height in order to have an objective measure for the integrity of the descending motor tracts in normal horses. Objective: To obtain reference values for onset latency and peak-to-peak amplitude of magnetic motor evoked potentials (MMEPs) and to evaluate the possible effect of height, age and gender on the neurophysi...
Effect of oral administration of dantrolene sodium on serum creatine kinase activity after exercise in horses with recurrent exertional rhabdomyolysis. To determine the effect of oral administration of dantrolene sodium on serum creatine kinase (CK) activity after exercise in horses with recurrent exertional rhabdomyolysis (RER). Methods: 2 healthy horses and 5 Thoroughbreds with RER. Methods: 3 horses received 2 doses of dantrolene (4, 6, or 8 mg/kg, p.o., with and without withdrawal of food) 2 days apart; 90 minutes after dosing, plasma dantrolene concentration was measured spectrofluorometrically. On the basis of these results, 5 Thoroughbreds with RER from which food was withheld received dantrolene (4 mg/kg) or an inert treatment (water ...
Therapeutic clenbuterol treatment does not alter Ca2+ sensitivity of permeabilized fast muscle fibres from exercise trained or untrained horses. Clenbuterol is a beta2-adrenoceptor agonist primarily used for treating bronchospasm and alleviating the symptoms of chronic obstructive pulmonary disease (COPD) in the horse. In other species (rats, mice, sheep, and cattle), chronic high doses of clenbuterol (typically in the milligram per kilogram body weight range) has been shown to cause a muscle directed protein anabolic response. Clenbuterol can also modify muscle fibre composition and therefore potentially affect muscle function. This has implications for the performance of exercising horses being treated with therapeutic doses of clenb...
Effect of controlled exercise on middle gluteal muscle fibre composition in Thoroughbred foals. Most racehorses are trained regularly from about age 18 months; therefore, little information is available on the effect of training in Thoroughbred foals. Objective: Well-controlled exercise could improve muscle potential ability for endurance running. Methods: Thoroughbred foals at age 2 months were separated into control and training (treadmill exercise) groups and samples obtained from the middle gluteal muscle at 2 and 12 months post partum. Muscle fibre compositions were determined by histochemical and electrophoretical techniques and succinic dehydrogenase (SDH) activity was analysed in...
Myosin heavy chain profiles and body composition are different in old versus young Standardbred mares. There are limited data on age-related changes in body composition or skeletal muscle in the horse. Therefore, the purpose of this study was to investigate any differences in muscle myosin heavy chain (MHC) and body composition associated with aging. Twenty-three young (4-8 years) and eight old (20+ years) unfit Standardbred mares were evaluated. Rump fat thickness was measured using B-mode ultrasound and per cent body fat (% fat) was calculated. Needle muscle biopsies were obtained from right gluteus medius muscle. MHC composition was determined via sodium dodecyl sulphate-polyacrylamide gel e...
Epidemiologic characteristics and management of polysaccharide storage myopathy in Quarter Horses. To characterize onset and clinical signs of polysaccharide storage myopathy (PSSM) in a well-defined population of affected Quarter Horses, identify risk factors for PSSM, determine compliance of owners to dietary and exercise recommendations, and evaluate the efficacy of dietary and exercise recommendations. Methods: 40 Quarter Horses with PSSM and 37 unaffected control horses. Methods: Owners of horses with PSSM completed a retrospective questionnaire concerning their horse's condition. Results: Between horses with PSSM and control horses, no significant differences were found in sex distrib...
Clinical and pathologic findings in two draft horses with progressive muscle atrophy, neuromuscular weakness, and abnormal gait characteristic of shivers syndrome. Two Belgian geldings, 4 and 14 years old, respectively, with muscle atrophy, weakness, and abnormal gait characteristic of severe advanced shivers were examined clinically and on necropsy. Neurologic examination revealed no evidence of ataxia, and the clinical diagnosis was neuromuscular weakness and shivers. Necropsies of both horses, including examination of pituitary, brain, spinal cord, spinal roots and ganglia, and peripheral nerves, revealed no gross or histologic abnormalities. Examination of multiple skeletal muscle specimens revealed chronic myopathic changes and periodic acid-Schiff ...
Experimental analysis of error sources in fibre type counts of biopsies in horses. The contribution to total variance of different error sources in fibre type counts of equine gluteus medius muscle biopsies was determined to quantify and possibly improve the resolution of the method. Fibre types were defined on the basis of myosin heavy chain immunostaining. Errors were determined at levels: (1) positioning the insertion channel, (2) positioning the needle tip (3) biopsy heterogeneity (4) observer interpretation. Errors at levels 1 and 2 were considerable. Confidence intervals for individual observations were +/- 10-15%. In longitudinal studies a group size of 4 animals is n...
Multiple cutaneous leiomyomas in the perineum of a horse. Multiple cutaneous masses developed in the perineum of a 14-year-old Saddlebred stallion over a period of approximately 5 years. Clinically, the masses ranged in size from 3- to 9-mm diameter and were not ulcerated, painful, or pruritic. Three of the masses were surgically excised and submitted for microscopic evaluation. The masses were dome shaped to nodular, located in the superficial dermis, and composed of haphazardly arranged bundles of plump spindle-shaped cells. The tumor cells immunoreacted with monoclonal antibodies directed against desmin, muscle-specific actin, and smooth muscle ac...
Standardization of transcranial magnetic stimulation in the horse. The influence of coil position on the peak-to-peak amplitude and onset latency of transcranial magnetic motor evoked potentials (MMEPs) in the extensor carpi radialis and cranial tibial muscles of horses was evaluated. Seven different stimulating coil positions were obtained by constructing a frame on the forehead. Two stimulation intensities (80% and 100% of maximal stimulator output) and two different coil currents (clockwise and counter-clockwise) were tested. For both recording sites MMEPs with the shortest onset latency and the largest peak-to-peak amplitude were detected when the coil wa...
