Muscle fiber types in horses refer to the classification of muscle fibers based on their metabolic and contractile properties. These fibers are categorized into different types, primarily type I (slow-twitch) and type II (fast-twitch), with type II further subdivided into type IIa and type IIb. Type I fibers are known for their endurance capabilities and rely on aerobic metabolism, whereas type II fibers are associated with strength and speed, utilizing anaerobic pathways. The distribution and proportion of these muscle fiber types can vary significantly among horse breeds and individuals, influencing their performance in various equestrian disciplines. This page compiles peer-reviewed research studies and scholarly articles that investigate the characteristics, distribution, and functional implications of muscle fiber types in equine physiology and performance.
Lungu GM, Barshick MR, Shafron AJ, El-Kadi SW, Williams BD, Wesolowski LT, Disilvestro AN, White-Springer SH, Johnson SE.High-intensity exercise in horses resulting in fatigue requires a better understanding of biomarkers defining the condition such that protocols detailing the return to work can be established. This study examined blood metabolite profiles after multiple sessions of high-intensity exercise to define physiological exhaustion. Adult Thoroughbred geldings (n = 10) underwent a standardized exercise test (SET) on a high-speed treadmill, with BHB, BCAAs, alanine, lactate, and CK measurements at regular intervals up to 6 h post-SET. Before and 24 h post-SET gluteus medius muscle samples were t...
Campos Schweitzer A, Mespoulhes-Rivière C, Perkins JD, Ducharme NG, Piercy RJ, Lynch N, Rossignol F.To evaluate functional and histopathologic outcomes of standing selective laryngeal reinnervation using the spinal accessory nerve (SAN) in horses with experimentally induced recurrent laryngeal neuropathy (RLN). Methods: Five Thoroughbred mares. Methods: Prospective cohort study. Methods: The horses underwent left recurrent laryngeal neurectomy followed 8 weeks later by selective laryngeal reinnervation using the SAN. Follow-up evaluations at 4.5, 6, 8, and 12 months included treadmill exercising endoscopy, ultrasonography of intrinsic laryngeal muscles, and percutaneous electrical stimul...
Valberg SJ, Williams ZJ, Ames EG, Mickelson JR, Nout-Lomas YS, Landolt G, Sanz M, Gardner K.Equine myotonic dystrophy (eMD) is a rare neuromuscular disorder of undetermined origin marked by muscle hypertrophy and stiffness, dystrophic muscle histopathology, and myotonic discharges. In humans, myotonic dystrophy (DM) arises from trinucleotide repeat expansions in dystrophia myotonica protein kinase (DMPK) (DM1) or tetranucleotide expansions in cellular nucleic acid-binding protein (CNBP) (DM2), which disrupt mRNA processing and induce embryonic splicing patterns across multiple genes. In 6 eMD Quarter Horse types, (2-36 months-of-age) and 8 control Quarter Horses we determined: (1) fi...
Arevalo-Turrubiarte M, Edling CE, Moller-Levet C, Forbes B, Kemp V, Weir J, Marr C, Lewis R, Jeevaratnam K.The initiation and maintenance of atrial fibrillation have been associated with physiological alterations in myocardial sleeves of the pulmonary veins (PVs). Gene expression profiles of the myocardial sleeves of the PVs in healthy (n = 3) and paroxysmal atrial fibrillation (PAF) (n = 6) thoroughbred horses (Equus caballus) were studied. Tissue collected from the left superior PV, adjacent to the left atrium, was analyzed by RNA sequencing. Gene Set Enrichment Analysis demonstrated positive enrichment of gene ontology biological processes related to muscle and endothelial cell development, cell...
Feng M, Hall TJ, MacHugh DE, Katz LM, Hill EW.Early skeletal muscle development is critical for young racehorses, yet research on the transcriptional changes during this period is limited. Additionally, the impact of age on the transcriptional response to exercise training in equine athletes is not well understood. A transcriptome-wide analysis of differential gene expression in skeletal muscle was performed for five untrained Thoroughbred horses sampled at rest at two years old (UR2) and three years old (UR3). A total of 136 differentially expressed genes (DEGs) were identified, with 95 increased and 41 decreased in expression. GO enrich...
Fresa K, Catandi GD, Gonzalez-Castro R, Omar A, Whitcomb LA, Cheng MH, Chen TW, Carnevale EM, Chicco AJ.Advancing age is associated with a decline in fertility and functional capacity, which may result in part from suboptimal nutrition and impaired mitochondrial function. Dietary essential polyunsaturated fatty acids (PUFA) are broadly recommended to mitigate weight loss and reduce risk of chronic disease in aged populations, but their effects on mitochondrial function are less clear. The present study investigated the impacts of dietary supplementation with essential omega-3 PUFA (flaxseed oil; N3) or omega-6 PUFA (corn oil, N6) on blood, muscle and follicular cell fatty acid composition and mi...
Li X, Meng C, Xue Y, Shen Z, Ren W, Zeng Y, Meng J.Skeletal muscle is the largest organ system in mammals. To investigate the differences in energy metabolism across various skeletal muscles in Yili horses, this study examined muscle fiber type distributions through immunohistochemical staining of muscles, including the splenius, triceps brachii, longissimus dorsi, and gluteus medius. The splenius and gluteus medius muscles, which exhibited the greatest differences in the proportion of slow-twitch fiber area, were selected for further comparison of differential metabolites and transcriptomic expression profiles between slow-twitch and fast-twi...
Melanie Catanchin CS, Bell J, Labens R, Quinn CT.Detomidine hydrochloride is an alpha adrenoceptor agonist that is commonly used in equine practice to provide sedation and analgesia for horses undergoing standing procedures. Reported effects following intravenous administration of detomidine in horses include bradycardia, bradyarrhythmias, transient hypertension, sweating, piloerection and dose-dependent sedation, ataxia and analgesia. This case report describes a novel response characterised by tachycardia and profound muscle tremors following the administration of intravenous detomidine to a horse undergoing a standing procedure.
Wang T, Li M, Ren W, Meng J, Yao X, Chu H, Yao R, Zhai M, Zeng Y.Yili horses undergo coordinated physiological adaptations across systems in response to customized training. This study aimed to clarify the molecular mechanisms of these adaptations by integrating analyses of cardiac function and multi-omics (lipidomics, transcriptomics, miRNomics). We collected whole blood samples from ten Yili horses before and after 12 weeks of specialized racing training to perform these analyses. Results showed training induced adaptive cardiac remodeling, with substantial increases in LVIDd and LVIDs. At the molecular level, this was accompanied by extensive blood lipid...
Wang T, Yang X, Ren W, Meng J, Yao X, Chu H, Yao R, Zhai M, Zeng Y.Exercise performance is a critical trait for evaluating the economic and breeding value of working and athletic horses, with cardiac structure and function serving as essential physiological determinants of athletic capacity. This study aimed to investigate the multi-omics response mechanisms associated with varying degrees of cardiac remodeling under identical exercise intensity. Twenty 2-year-old Yili horses were selected and categorized based on echocardiographic parameters into a high cardiac remodeling group (BH; EDV > 500 mL, SV > 350 mL, EF > 66%) and a low cardiac remodeling group (BL;...
Hanousek K, O'Hara V, Riddell DO, Piercy RJ.In Thoroughbred horses, a highly prevalent short interspersed nuclear element (SINE) mutation in the myostatin gene (MSTN) promoter influences circulating myostatin concentration and is associated with muscle morphology, fracture risk and optimal race distance. Our prior data reveal that within horses there is substantial variation in serum myostatin concentration, particularly in MSTN heterozygotes and wild type horses but it was unclear whether such variation relates to within-horse differences or to environmental or temporal effects. Here we report the intra-horse consistency of circulating...
Janzen N, Sander J, Terhardt M, Mallek M, Smith H, Witt P, Theelen MJP.The case of a young foal poisoned by maple toxin is described. It showed signs of myopathy caused by ingesting life-threatening amounts of maple toxin. Some maple trees (Acer species) can pose a health risk to grazing horses. The leaves, seeds and shoots contain hypoglycin A (HGA) and methylencyclopropylglycine (MCPRG) and can cause life-threatening atypical myopathy.
Huang Q, Ren W, Shan D, Su Y, Li Z, Li L, Wang R, Ma S, Wang J.This study aimed to compare blood samples from Yili horses with outstanding and average performance in 5000 m races through transcriptome sequencing, identify key differentially expressed genes, lncRNAs, and circRNAs, as well as related enriched pathways, and elucidate their regulatory networks. This study used six healthy four-year-old Yili stallions as subjects, divided into an excellent group (E group, = 3) and an ordinary group (O group, = 3) based on their 5000-m race performance. Blood RNA-Seq technology was used to analyze differentially expressed mRNAs, lncRNAs, and circRNAs. A total...
Wang J, Li Z, Li L, Wang R, Ma S, Su Y, Shan D, Huang Q.Kazakh horses are renowned for their endurance and adaptability, with distinct muscle groups such as the longissimus dorsi (LD) and biceps femoris (BF) muscles serving specialized functions. However, the molecular mechanisms underlying the functional specialization of these muscles in Kazakh horses remain poorly understood. This study aims to address this gap by utilizing single-cell RNA sequencing (scRNA-seq) to investigate the transcriptomic differences between these muscle groups, with a focus on understanding their molecular adaptations. Our analysis revealed that the BF muscle, specialize...
Wubuli A, Su Y, Yao X, Meng J, Wang J, Zeng Y, Li L, Ren W.The Kazakh horse, a versatile breed, is renowned for stable genetic performance and strong tolerance to coarse feed. Sex is a key factor influencing skeletal muscle development. However, the mechanisms underlying sex-specific regulation of equine muscle growth remain obscure. This study employed transcriptomic analysis to investigate sex-associated molecular differences in skeletal muscle of Kazakh horses. The experimental cohort comprised four three-year-old Kazakh stallions and four three-year-old Kazakh mares. After slaughter, six groups of muscle samples were collected immediately, includi...
Tranquille C, Nankervis K, Tacey J, Hopkins E, Deckers I, Walker V, MacKechnie-Guire R, Newton R, Murray R.Water treadmill (WT) exercise has become a popular tool for equine training and rehabilitation. However, few studies describe the long-term effects of WT exercise in low water on muscle development (MD). This study's objectives were to compare MD changes over a 40-week period in sport horses that regularly used WT in low water within training (Group WTH, = 55) and a control group that did not (control, = 28). Subjective MD assessments were undertaken using an adaptation of a previously published method at weeks 0, 20 and 40. For Group WTH, MD significantly increased in the neck, pelvis and h...
Ding W, Gong W, Bou T, Shi L, Lin Y, Shi X, Li Z, Wu H, Dugarjaviin M, Bai D.Speed is not only the primary objective of racehorse breeding but also a crucial indicator for evaluating racehorse performance. This study investigates a newly developed racehorse breed in China. Through whole-genome resequencing, we selected 60 offspring obtained from the crossbreeding of Thoroughbred horses and Xilingol horses for this study. This breed is tentatively named "Grassland-Thoroughbred", and the samples were divided into two groups based on racing ability: 30 racehorses and 30 non-racehorses. Based on whole-genome sequencing data, the study achieved an average sequencing depth o...
Wubulikasimu M, Liu J, Yao X, Meng J, Wang J, Zeng Y, Li L, Ren W.Kazakh horses, a distinguished breed in China known for their dual-purpose use in milk and meat production, exhibit early maturation, tolerance to coarse feeding, and strong resistance to environmental stress. However, the gene expression differences across various muscle tissues of Kazakh horses have yet to be elucidated. In this study, transcriptomic sequencing was performed on muscle tissues from three anatomical regions of Kazakh horses, including the longissimus dorsi (Gb), external oblique (Gf), and diaphragm (Gg) muscles. In the Gb and Gf groups, 426 differentially expressed genes (DEGs...
Frontiers in geneticsJuly 18, 2025
Volume 16 1630614 doi: 10.3389/fgene.2025.1630614
Gong W, Ding W, Bou T, Shi L, Lin Y, Shi X, Li Z, Wu H, Dugarjaviin M, Bai D.Ferulic acid (FA), a natural antioxidant, has attracted considerable attention for its regulatory potential in skeletal muscle development, energy metabolism, and muscle fiber type transformation. Unassigned: This study established a research system based on Mongolian horse skeletal muscle satellite cells to elucidate the molecular basis by which ferulic acid regulates muscle fiber type transformation through a non-coding RNA interaction network. Unassigned: A total of 18 differentially expressed miRNAs (DEMIRs) and 128 differentially expressed lncRNAs (DELs) were identified through transcript...
Gong W, Ding W, Bou T, Shi L, Lin Y, Shi X, Wu H, Li Z, Dugarjaviin M, Bai D.Ferulic acid (FA), a natural antioxidant and major active component in Angelica sinensis, has beneficial effects on skeletal muscle health; however, its role in modulating muscle fiber type composition Mongolian horse remains unclear. In this study, we found that FA promotes the proliferation of Mongolian horse skeletal muscle satellite cell (MuSCs), upregulates the expression of fast-twitch muscle marker genes (e.g., MYH2), and downregulates the expression of slow-twitch markers (e.g., MYH7). RNA-seq revealed that FA activates the HIF-1 signaling pathway, significantly increasing PDK1 express...
Bauquier J, Takahashi C, Rosales C, Pitt J.There is limited published information on Malva parviflora toxicosis in horses. Four previously reported cases all resulted in death or euthanasia. The aim of this cluster investigation was to describe historical, clinical and clinicopathological findings of four ponies with suspected M. parviflora toxicosis and compare these to previously reported cases. Historical, clinical and clinicopathological findings were collated. Ponies were grazing pasture of approximately >90% M. parviflora. Pony 1 died rapidly without veterinary examination. Pony 2 was examined for prolonged recumbency attribut...
Liu Y, Liu Y, Bai D, Dugarjaviin M, Zhang X.Skeletal muscle satellite cells are muscle stem cells that play an important role in the growth, development, and repair of skeletal muscle as well as in the locomotor performance of the animal body. Lysine is the first limiting amino acid and is involved in multiple metabolic pathways in the organism to maintain overall physiological requirements. In this study, Mongolian horse satellite cells were cultured using lysine culture solution at different concentrations, and the proliferative capacity of satellite cells was detected by the cck-8 assay, and the optimal culture concentration was sele...
Li C, Li X, Liu K, Xu J, Yu J, Liu Z, Mach N, Ni W, Liu C, Zhou P, Wang L, Hu S.Gut microbes play a vital role in host physiology, but whether specific bacterial functions contribute to the exceptional athletic performance of racehorses needs to be better understood. Here, we identify an association of gut butyrate-producing bacteria with athletic performance in racehorses (Thoroughbred horse). Butyrate-producing bacteria and microbial butyrate synthesis genes were significantly enriched in the racehorse gut, and the GC-MS results confirmed this conclusion. Using a mouse model, we demonstrated that sodium butyrate is sufficient to increase treadmill run time performance. ...
Connysson M, Jansson A.It is generally accepted that plasma muscle enzyme activity of creatine kinase (CK) and aspartate aminotransferase (AST) may increase in racehorses after exercise and racing, indicating muscle fibre damage and/or increased leakage from muscle fibres. However, other studies suggest that starch intake might influence plasma muscle enzyme activity reported postexercise. This study aimed to evaluate the effect of different starch allowances on plasma muscle enzyme activity in Standardbred trotters in professional training. Seventy-six horses from five professional trainers were sampled pre- and po...
Hansen S, Hopster-Iversen C, Berg L, Fjeldborg J, Massey C, Piercy RJ, Carstensen H.Exertional myopathies are recognised as a cause of poor performance in equines. In Icelandic horses presenting reduced performance and/or multi-limb lameness, no specific myopathy has been identified. Objective: To characterise the clinical presentation and histopathological findings in muscle biopsy samples from Icelandic horses demonstrating poor performance. Methods: Case series. Methods: Phenotypic characteristics, clinical examination and diagnoses of 17 Icelandic horses were studied. All horses had a resting serum creatine kinase (CK) and aspartate transaminase activities measured, and C...
Ding W, Gong W, Bou T, Shi L, Lin Y, Wu H, Dugarjaviin M, Bai D.Muscle fibers, as the fundamental units of muscle tissue, play a crucial role in determining skeletal muscle function through their growth, development, and composition. To investigate changes in muscle fiber types and their regulatory mechanisms in Mongolian horses (MG), Xilingol horses (XL), and Grassland-Thoroughbreds (CY), we conducted histological and bioinformatic analyses on the gluteus medius muscle of these three horse breeds. Immunofluorescence analysis revealed that Grassland-Thoroughbreds had the highest proportion of fast-twitch muscle fibers at 78.63%, while Mongolian horses had ...
Carvalho JRG, Sales NAA, Littiere TO, Costa GB, Castro CM, Polisel EEC, Orsi JB, Ramos GV, Santos IFC, Gobatto CA, Manchado-Gobatto FB, Ferraz GC.Several studies have explored alternatives to enhance the performance, health, and safety of sports horses. One promising method involves the use of vibrating platforms (VP), which offer passive exercise stimulation via mechanical oscillations distributed throughout the body. This type of exercise is referred to as whole-body vibration (WBV) and is an emerging strategy for accelerating muscle recovery. This study examined the dynamics of proteins responsible for transporting monocarboxylates (MCT1 and MCT4), and their relationship with lactatemia and acid-base balance in connection with WBV re...
Firshman AM, Valberg SJ.Type 1 Polysaccharide Storage Myopathy (PSSM1) is an autosomal dominant glycogen storage disorder affecting more than 20 breeds of horses that can present with a variety of signs, including exertional rhabdomyolysis (ER). It is diagnosed by genetic testing or muscle biopsies containing muscle fibers with abnormal amylase-resistant polysaccharide. Type 2 PSSM has recently been subdivided. PSSM2-ER is a glycogen storage disorder identified in Quarter Horses that causes ER and is diagnosed by muscle biopsy as its genetic basis is unknown. Both PSSM1 and PSSM2-ER respond well to a low nonstructura...
Finno CJ, McKenzie E.Nutritional deficiencies of vitamin E and selenium can occur alone or concurrently. Prolonged and sustained deficiency of either or both nutrients can lead to profound clinical disease. Selenium deficiency can also result in signs of cardiac disease, upper gastrointestinal dysfunction, and abortion or the birth of weak foals. Deficiencies can usually be readily established by evaluating the dietary intake of individuals and by measurement of blood concentrations of these nutrients. Treatment of clinical disease is not always successful and prolonged morbidity and mortality can be encountered; ...
McGowan C.Traumatic muscle injuries are likely to be frequent in athletic horses yet are often overlooked. These injuries usually involve internal (intrinsic) trauma, and particularly occur in athletic horses exercising at higher intensities, at unaccustomed workloads, or performing work requiring sudden acceleration, deceleration, and/or direction changes. These injuries can present with signs ranging from acute pain and lameness in a localized region to unexplained elevations of muscle enzymes on routine blood tests with or without poor performance. They include exercise-induced muscle damage such as ...
Petersen JL, Mickelson JR, Rendahl AK, Valberg SJ, Andersson LS, Axelsson J, Bailey E, Bannasch D, Binns MM, Borges AS, Brama P, da Câmara Machado A....Intense selective pressures applied over short evolutionary time have resulted in homogeneity within, but substantial variation among, horse breeds. Utilizing this population structure, 744 individuals from 33 breeds, and a 54,000 SNP genotyping array, breed-specific targets of selection were identified using an F(ST)-based statistic calculated in 500-kb windows across the genome. A 5.5-Mb region of ECA18, in which the myostatin (MSTN) gene was centered, contained the highest signature of selection in both the Paint and Quarter Horse. Gene sequencing and histological analysis of gluteal muscle...
Heizmann CW, Berchtold MW, Rowlerson AM.The physiological role of the Ca2+-binding protein parvalbumin in skeletal muscle has been investigated by measuring the parvalbumin content by HPLC in a variety of mammalian muscles, including man, and comparing the results with the respective muscle relaxation properties and fiber type compositions. The parvalbumin concentrations were highest in the skeletal muscles of the smallest animal investigated (mouse, gastrocnemius: 4.9 g/kg), which has the highest relaxation speed, and lowest in the larger animals (horse, deep gluteal muscle: less than or equal to 0.001 g/kg) and man (vastus, tricep...
Rome LC, Sosnicki AA, Goble DO.1. To explore how maximum velocity of shortening (Vmax) of fibres varies within one muscle and how Vmax varies with body size, we measured Vmax of muscle fibres from soleus muscle of a large animal, the horse. 2. Vmax was determined by the slack test on skinned single muscle fibres at 15 degrees C during maximal activation (pCa = 5.2). The fibre type was subsequently determined by a combination of single-cell histochemistry and gel electrophoresis of the myosin light chains. 3. Vmax values for the type I, IIA and IIB muscle fibres were 0.33 +/- 0.04 muscle lengths/s (ML/s) (+/- S.E.M., n = 6),...
Carraro U, Kern H, Gava P, Hofer C, Loefler S, Gargiulo P, Mosole S, Zampieri S, Gobbo V, Ravara B, Piccione F, Marcante A, Baba A, Schils S, Pond A....There is something in our genome that dictates life expectancy and there is nothing that can be done to avoid this; indeed, there is not yet any record of a person who has cheated death. Our physical prowess can vacillate substantially in our lifetime according to our activity levels and nutritional status and we may fight aging, but we will inevitably lose. We have presented strong evidence that the atrophy which accompanies aging is to some extent caused by loss of innervation. We compared muscle biopsies of sedentary seniors to those of life long active seniors, and show that these groups i...
Liu JX, Höglund AS, Karlsson P, Lindblad J, Qaisar R, Aare S, Bengtsson E, Larsson L.This comparative study of myonuclear domain (MND) size in mammalian species representing a 100,000-fold difference in body mass, ranging from 25 g to 2500 kg, was undertaken to improve our understanding of myonuclear organization in skeletal muscle fibres. Myonuclear domain size was calculated from three-dimensional reconstructions in a total of 235 single muscle fibre segments at a fixed sarcomere length. Irrespective of species, the largest MND size was observed in muscle fibres expressing fast myosin heavy chain (MyHC) isoforms, but in the two smallest mammalian species studied (mouse and r...
Lindholm A, Piehl K.LINDHOLM, ARNE and KARIN PIEHL: Acta vet. scand. 1974, , 287–309. — Measurements of metabolites, electrolytes, water, RNA and protein concentrations, the activity of certain muscle enzymes (SDH and PFK) and muscle fibre composition were made on biopsy specimens from the gluteus medius muscle of 68 standardbred horses, ½ to 8 years old. The muscle fibres were classified in 3 major categories, slow twitch (ST), fast twitch and high oxidative (FTH) and fast twitch (FT) fibres. The percentage of FTH fibres was higher after the age of 4 years, averaging 54 %. ST fibres comprised 24 % and this...
Votion DM, Gnaiger E, Lemieux H, Mouithys-Mickalad A, Serteyn D.Within the animal kingdom, horses are among the most powerful aerobic athletic mammals. Determination of muscle respiratory capacity and control improves our knowledge of mitochondrial physiology in horses and high aerobic performance in general. Results: We applied high-resolution respirometry and multiple substrate-uncoupler-inhibitor titration protocols to study mitochondrial physiology in small (1.0-2.5 mg) permeabilized muscle fibres sampled from triceps brachii of healthy horses. Oxidative phosphorylation (OXPHOS) capacity (pmol O(2) • s(-1) • mg(-1) wet weight) with combined Complex...
Dunnett M, Harris RC.The aim of this work was to test the hypothesis that in vivo carnosine biosynthesis is dependent upon endogenous beta-alanine availability, by studying the effect of sustained dietary beta-alanine supplementation in the horse on the carnosine concentration in types I, IIA and IIB skeletal muscle fibres. The diets of 6 Thoroughbred horses were supplemented 3 times/day with beta-alanine (100 mg/kg bwt) and L-histidine (12.5 mg/kg bwt) for a period of 30 days. Percutaneous biopsies of the m. gluteus medius from a depth of 6 cm were taken on the days immediately before and after the supplementatio...
Tateo A, De Palo P, Ceci E, Centoducati P.To investigate rheological and chemical characteristics of the meat from Italian Heavy Draft horse, 24 foals (12 males and 12 females) were weaned at 6 mo, reared and fed in the same way, and slaughtered at 11 mo of age. The results obtained showed that there were no significant differences between the sexes but that the muscle type is a significant variation source. The rectus femoris muscle was lighter, and the biceps femoris had a lower a* index than longissimus dorsii, rectus femoris, and semimembranosus muscle. The most tender muscle was the semitendinosus, and the toughest even after coo...
Byrd SK, McCutcheon LJ, Hodgson DR, Gollnick PD.This study examined the effects of acute high-intensity exercise on the rate and capacity of Ca2+ uptake and Ca2+-stimulated adenosinetriphosphatase (ATPase) activity of the sarcoplasmic reticulum and the reversibility of these effects. Thoroughbred horses were run at maximal O2 uptake on a high-speed treadmill until fatigued. Muscle temperatures and biopsy samples were collected at rest, immediately after exercise, and 30 and 60 min after exercise. Blood samples were collected at rest and 5 min after exercise. Muscle and blood (lactate concentration) were three- and fivefold greater than pre-...
Rivero JL, Ruz A, Martí-Korff S, Estepa JC, Aguilera-Tejero E, Werkman J, Sobotta M, Lindner A.This study examined the effects of the intensity and duration of exercise on the nature and magnitude of training adaptations in muscle of adolescent (2-3 yr old) racehorses. Six thoroughbreds that had been pretrained for 2 mo performed six consecutive conditioning programs of varying lactate-guided intensities [velocities eliciting blood lactate concentrations of 2.5 mmol/l (v2.5) and 4 mmol/l (v4), respectively] and durations (5, 15, 25 min). Pre- and posttraining gluteus muscle biopsies were analyzed for myosin heavy chain content, fiber-type composition, fiber size, capillarization, and fi...
Serrano AL, Quiroz-Rothe E, Rivero JL.Twenty-four 4-year-old Andalusian (Spanish breed) stallions were used to examine the plasticity of myosin heavy chain (MHC) phenotype and the metabolic profile in horse skeletal muscle with long-term endurance-exercise training and detraining. Sixteen horses underwent a training programme based on aerobic exercises for 8 months. Afterwards, they were kept in paddocks for 3 months. The remaining eight horses were used as controls. Three gluteus medius muscle biopsy samples were removed at depths of 20, 40 and 60 mm from each horse before (month 0), during (month 3) and after (month 8) training,...
Kawai M, Minami Y, Sayama Y, Kuwano A, Hiraga A, Miyata H.We examine the muscle fiber population and metabolic properties of skeletal muscles from the whole body in Thoroughbred horses. Postmortem samples were taken from 46 sites in six Thoroughbred horses aged between 3 and 6 years. Fiber type population was determined on muscle fibers stained with monoclonal antibody to each myosin heavy chain isoform and metabolic enzyme activities were determined spectrophotometrically. Histochemical analysis demonstrated that most of the muscles had a high percentage of Type IIa fibers. In terms of the muscle characteristic in several parts of the horse body, th...
Petersen JL, Valberg SJ, Mickelson JR, McCue ME.Two variants in the equine myostatin gene (MSTN), including a T/C SNP in the first intron and a 227-bp SINE insertion in the promoter, are associated with muscle fiber type proportions in the Quarter Horse (QH) and with the prediction of race distance propensity in the Thoroughbred (TB). Genotypes from these loci, along with 18 additional variants surrounding MSTN, were examined in 301 horses of 14 breeds to evaluate haplotype relationships and diversity. The C allele of intron 1 was found in 12 of 14 breeds at a frequency of 0.27; the SINE was observed in five breeds, but common in only the T...
Kearns CF, McKeever KH, Abe T.Locomotion requires skeletal muscle to sustain and generate force. A muscle's force potential is proportional to its weight. Since the larger the muscle the larger its potential power output, a better understanding of the proportion of skeletal muscle a horse possesses may lead to a better understanding of horse performance. Several techniques exist to assess body composition, which include dual energy X-ray absorption, underwater (hydrostatic) weighing, derivation from total body water, bio-electric impedance, air displacement, body condition scoring, cadaver dissection and ultrasound. The re...
Dunnett M, Harris RC.The combined solid-phase extraction (Isolute PRS columns) and reversed-phase gradient HPLC method presented provides a sensitive, reproducible and selective quantification of carnosine, balenine, homocarnosine, histidine, 1-methylhistidine and 3-methylhistidine in equine and camel muscle and individual muscle fibres. Recoveries were 91-115%. Lower limits of detection were 0.005-0.010 mmol kg-1 dry muscle. The compounds were isolated from other physiological amino acids and small peptides and resolved within a single chromatographic run of 55 min. Concentrations of these compounds in equine myo...
Kayar SR, Hoppeler H, Mermod L, Weibel ER.Individual mitochondria were reconstructed from ultrathin serial sections of selected muscle fibers in the M. semitendinosus of a horse, over a length of nearly two sarcomeres. Mitochondria were found to be highly variable, with size and complexity of single mitochondria increasing with the fractional part of a fiber occupied by mitochondria. In fibers with a mitochondrial volume density of less than 4%, corresponding to the mitochondrial content of fast-twitch glycolytic fibers, mitochondria were generally rather simple cylindrical shapes, oriented parallel to the myofibrils. In fibers with a...
Eivers SS, McGivney BA, Gu J, MacHugh DE, Katz LM, Hill EW.Peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) has emerged as a critical control factor in skeletal muscle adaptation to exercise, acting via transcriptional control of genes responsible for angiogenesis, fatty acid oxidation, oxidative phosphorylation, mitochondrial biogenesis and muscle fibre type composition. In a previous study, we demonstrated a significant increase in mRNA expression for the gene encoding PGC-1α (PPARGC1A) in Thoroughbred horse skeletal muscle following a single bout of endurance exercise. In this study, we investigated mRNA expression changes i...
Chiaradia E, Avellini L, Rueca F, Spaterna A, Porciello F, Antonioni MT, Gaiti A.Since it has been suggested that lipid peroxidation following free radical overproduction may be one of the causes of physical exercise-induced myopathies and hemolysis in horses, we looked for the possible relationships between these phenomena and muscle fiber damage. We use a homogeneous group of Maremmana stallions which, after a 3-month training period, underwent a series of physical exercises of increasing intensity. We determined the contents of malondialdehyde (MDA), one of the main lipid peroxidation end-products, and glutathione the substrate of one of the most important free radical ...
Snow DH, Guy PS.Skeletal muscle of the equine was differentiated into three fibre types according to myosin ATPase (pH 9.4) and succinic dehydrogenase activity. The percentage of these types was determined in the musculus deltoideus, m triceps brachii caput longum, m gluteus medius, m semitendinosis, m biceps femoris and m vastus lateralis of the thoroughbred, Shetland pony, pony, heavy hunter and donkey. In addition the m gluteus medius was examined in the arab and American racing quarterhorse. High myosin ATPase activity fibres varied from a mean of 93.2 per cent in the m gluteus medius of the quarterhorse ...
Rivero JL, Serrano AL, Henckel P, Agüera E.Triplicate biopsies from three different depths of the gluteus medius muscle were obtained in 36 endurance-raced horses, aged 8.42 +/- 2.85 yr. Twenty of the horses were considered excellent endurance performers according to the mean speed of their three fastest records in endurance events for the past 2 or 3 years, whereas 16 were moderate performers, with a mean racing speed < 12.5 km/h (in 120- to 180-km endurance rides), < 14 km/h (in 80- to 120-km endurance rides), or < 13.5 km/h (in 40- to 60-km endurance rides). Significant differences in muscle fiber type composition and fiber size wer...
Rivero JL, Serrano AL, Barrey E, Valette JP, Jouglin M.Combined methodologies of enzyme-linked immunosorbent assay (ELISA), sodium dodecyl sulphate polyacrilamide gel electrophoresis (SDS-PAGE), immunoblotting, traditional myofibrillar ATPase (mATPase) histochemistry and immunocytochemistry of whole biopsied samples were used to study myosin heavy chain (MHC) isoforms in the equine gluteus medius muscle. The ELISA technique allowed the quantification of the three MHC isoforms known to be present in different horse muscles: slow (MHC-I) and two fast (termed MHC-IIA and MCH-IIX). The SDS-PAGE method resolved MHCs in three bands: MHC-I, MHC-IIX and M...
Rivero JL, Hill EW.Skeletal muscles in horses are characterised by specific adaptations, which are the result of the natural evolution of the horse as a grazing animal, centuries of selective breeding and the adaptability of this tissue in response to training. These adaptations include an increased muscle mass relative to body weight, a great locomotor efficiency based upon an admirable muscle-tendon architectural design and an adaptable fibre-type composition with intrinsic shortening velocities greater than would be predicted from an animal of comparable body size. Furthermore, equine skeletal muscles have a ...
Armstrong RB, Essén-Gustavsson B, Hoppeler H, Jones JH, Kayar SR, Laughlin MH, Lindholm A, Longworth KE, Taylor CR, Weibel ER.The purpose of this study was to describe the relationships between 16 physiological, biochemical, and morphological variables presumed to relate to the oxidative capacity in quadriceps muscles or muscle parts in Standardbred horses. The variables included O2 delivery (blood flow) and mean capillary transit time (MTT) during treadmill locomotion at whole animal maximal O2 consumption (VO2max, 134 +/- 2 ml.min-1 x kg-1), capillary density and capillary-to-fiber ratio, myoglobin concentration, oxidative enzyme activities, glycolytic enzyme activities, fiber type populations, and fiber size. Thes...
Votion DM, Fraipont A, Goachet AG, Robert C, van Erck E, Amory H, Ceusters J, de la Rebière de Pouyade G, Franck T, Mouithys-Mickalad A, Niesten A....Limited information exists about the muscle mitochondrial respiratory function changes that occur in horses during an endurance season. Objective: To determine effects of training and racing on muscle oxidative phosphorylation (OXPHOS) and electron transport system (ETS) capacities in horses with high resolution respirometry (HRR). Methods: Mitochondrial respiration was measured in microbiopsies taken from the triceps brachii (tb) and gluteus medius (gm) muscles in 8 endurance horses (7 purebred Arabians and 1 crossbred Arabian) before training (T0), after two 10 week training periods (T1, T2)...
Mathieu-Costello O, Hoppeler H, Weibel ER.Capillary orientation (anisotropy) was compared in hindlimb muscles of mammals of different size and/or different aerobic capacity (dog, goat, pony, and calf). All muscles were fixed by vascular perfusion at sarcomere lengths ranging from 1.5 to 2.7 micron. The ratios of capillary counts per fiber cross-sectional area on two sets of sections (0 and 90 degrees) to the muscle fiber axis were used to estimate capillary anisotropy and the coefficient c(K,0) relating 1) capillary counts on transverse sections (a commonly used parameter to assess muscle capillarity) and 2) capillary length per volum...
Ravara B, Gobbo V, Carraro U, Gelbmann L, Pribyl J, Schils S.Functional Electrical Stimulation (FES) has been used extensively over several decades to reverse muscle atrophy during rehabilitation for spinal cord injury patients. The benefits of the technology are being expanded into other areas, and FES has been recently utilized for injury rehabilitation and performance enhancement in horses. Six retired horses (age from 10 to 17 yrs) that had been previously used mainly for dressage riding were selected for this study. Clinical evaluation found epaxial muscle spasms in all horses with minimal to no pelvic extension when manually palpated. FES treatmen...
Rivero JL, Talmadge RJ, Edgerton VR.The histochemical myofibrillar ATPase (mATPase) method is used routinely for identification of equine skeletal muscle fiber types, but important problems have been observed with the subdivision of fast fiber population when using this method. To verify the use of this qualitative method, a number of equine muscle biopsies were analyzed with a combination of histochemical, immunohistochemical, electrophoretic, and morphometric techniques. The influence of training on these interrelations was also evaluated. Methods: Five young (2-3 years old) thoroughbred horses were intensively trained for 8 m...
Snow DH, Harris RC, Gash SP.Four thoroughbred horses performed 4 gallops (G1-G4) with intervals of 5 min. With one exception, gallops were sustained at maximal speed over 620 m. Muscle biopsy samples of the middle gluteal and brachiocephalicus were taken before, during, and after exercise and assayed for ATP and intermediary metabolites. The results showed a major involvement of the brachiocephalicus, in addition to the middle gluteal, during galloping. In three horses, who were clearly fatigued, muscle ATP decreased by up to 50% by the end of G4. This was matched by an equal rise in inosine 5'-monophosphate. Pronounced ...
