Glycogen is a polysaccharide that serves as a primary form of energy storage in horses, predominantly found in the liver and muscle tissues. It acts as a readily available energy source that can be mobilized during periods of increased metabolic demand, such as exercise or stress. The synthesis and breakdown of glycogen are regulated by hormonal and enzymatic pathways, which are influenced by factors like diet, exercise, and overall health status. Understanding glycogen metabolism is important for optimizing performance, managing dietary needs, and preventing metabolic disorders in equine populations. This page compiles peer-reviewed research studies and scholarly articles that explore the role, regulation, and physiological implications of glycogen in equine health and performance.
Lacombe VA, Hinchcliff KW, Kohn CW, Reed SM, Taylor LE.Exercise depletes muscle glycogen stores, which could subsequently impair performance. Muscle glycogen replenishment is determined by substrate availability. Objective: To study the effects of feeding meals of varying glycaemic responses on blood concentrations of substrates used for glycogenesis in horses with exercise-induced glycogen depletion. Methods: In a 3-way crossover study, 7 horses received each of 3 isocaloric diets for 72 h after undergoing glycogen-depleting exercise: 1) a high soluble-carbohydrate diet, which induced a high-glycaemic (HGI) response; 2 and 3) a low soluble-carboh...
Bröjer J, Holm S, Jonasson R, Hedenström U, Essén-Gustavsson B.The degradation of glycogen and its two forms, proglycogen (PG) and macroglycogen (MG) has been studied in horses performing different types of exercise, but no information is available about the resynthesis of PG and MG after exercise. Objective: To determine the resynthesis of PG and MG in skeletal muscle after intermittent uphill exercise. Methods: At a training camp 9 well-trained Standardbred trotters performed a training session comprising a warm-up period, 7 repeated 500 m bouts of exercise on an uphill slope and a recovery period. Muscle biopsies (m. gluteus medius) for analysis of PG,...
Geor RJ, Larsen L, Waterfall HL, Stewart-Hunt L, McCutcheon LJ.No studies in horses have examined the effect of route of carbohydrate (glucose) administration on the rate of muscle glycogen storage following glycogen-depleting exercise. Objective: Glucose delivery from the gastrointestinal tract limits the rate of muscle glycogen storage following glycogen-depleting exercise. Methods: In a crossover design, 7 fit horses completed treadmill exercise (EX) on 3 occasions to deplete muscle glycogen by approximately 50%. After EX horses received: 1) i.v. glucose infusion (IV; 0.5 g/kg bwt/h for 6 h), 2) oral glucose boluses (OR; 1 g/kg bwt at 0, 2 and 4 h post...
McCue ME, Ribeiro WP, Valberg SJ.Controversy exists as to the prevalence of polysaccharide storage myopathy (PSSM) in breeds of horses and its impact on performance. Objective: To determine 1) the prevalence of PSSM in horses that presented with a neuromuscular disorder, as well as breed, sex and age distributions and clinical signs 2) effect of diagnostic criteria on prevalence, breed distribution and age of horses diagnosed with PSSM. Methods: Fresh frozen biopsies (n = 1426) submitted to the Neuromuscular Diagnostic Laboratory at the University of Minnesota were searched to identify horses diagnosed with PSSM. Horses with ...
Eto D, Yamano S, Hiraga A, Miyata H.There is little information about the muscle fibre recruitment pattern during sloped and flat track running in Thoroughbred horses. Objective: To examine the glycogen depletion pattern of each muscle fibre type during running on a flat and sloped treadmill. Methods: Thirteen Thoroughbred horses (3-9 years old) were used. They were initially subjected to incremental exercise tests on a treadmill at 10 and 0% inclines in each horse to determine running speed at 90 and 60% VO2max. Needle biopsy samples were obtained from the middle gluteal muscle immediately after the running at 90% VO2max for 4 ...
Zeyner A, Hoffmeister C, Einspanier A, Gottschalk J, Lengwenat O, Illies M.Quarter Horses are particularly susceptible to polysaccharide storage myopathy (PSSM). Nutritional therapy and possibly prophylaxis includes fat-supplemented diets whilst starch supply should be kept to a minimum. Objective: To investigate the glycaemic and insulinaemic response of clinically normal Quarter Horses to concentrates high in fat and low in starch. Methods: Twelve Quarter Horses were studied. The precondition for inclusion in the study population was that the horses had not shown clinical signs of myopathy. The Quarter Horses were fed according to a 4 x 4 Latin square design haylag...
Stewart-Hunt L, Geor RJ, McCutcheon LJ.Increased insulin sensitivity occurs after a period of exercise training, but the mechanisms underlying this training-associated increase in insulin action have not been investigated. Objective: To examine the effects of short-term endurance training (7 consecutive days) and a subsequent period of inactivity (5 days) on whole body insulin sensitivity and GLUT-4 protein and the activities of glycogen synthase (GS) and hexokinase (HK) in skeletal muscle. It was hypothesised that training would increase insulin sensitivity in association with increased GLUT-4 protein and activities of GS and HK, ...
Wagner ML, Valberg SJ, Ames EG, Bauer MM, Wiseman JA, Penedo MC, Kinde H, Abbitt B, Mickelson JR.Glycogen Branching Enzyme Deficiency (GBED), a fatal condition recently identified in fetuses and neonatal foals of the Quarter Horse and Paint Horse lineages, is caused by a nonsense mutation in codon 34 of the GBE1 gene, which prevents the synthesis of a functional GBE protein and severely disrupts glycogen metabolism. The aims of this project were to determine the mutant GBE1 allele frequency in random samples from the major relevant horse breeds, as well as the frequency with which GBED is associated with abortion and early neonatal death using the tissue archives from veterinary diagnosti...
Bröjer JT, Essén-Gustavsson B, Annandale EJ, Valberg SJ.To determine concentrations of proglycogen (PG), macroglycogen (MG), glucose, and glucose-6-phosphate (G-6-P) in skeletal muscle of horses with polysaccharide storage myopathy (PSSM) before and after performing light submaximal exercise. Methods: 6 horses with PSSM and 4 control horses. Methods: Horses with PSSM completed repeated intervals of 2 minutes of walking followed by 2 minutes of trotting on a treadmill until muscle cramping developed. Four untrained control horses performed a similar exercise test for up to 20 minutes. Serum creatine kinase (CK) activity was measured before and 4 hou...
Valentine BA, Cooper BJ.Muscle samples from 24 horses with polysaccharide storage myopathy were stained with periodic acid-Schiff (PAS) stain and were immunostained for ubiquitin. Abnormalities detected with PAS stain were coarse granular cytoplasmic aggregates of amylase sensitive glycogen, subsarcolemmal aggregates of glycogen, central amylase sensitive bodies, and a variety of subsarcolemmal to intracytoplasmic amylase resistant polyglucosan inclusions. All amylase resistant inclusions were positive for ubiquitin. Ubiquitin was also detected in many amylase sensitive inclusions. Based on morphologic findings and p...
Valentine BA, Flint TH, Fischer KA.Serial sections of formalin-fixed, paraffin-embedded muscle biopsy specimens from 28 Quarter Horse, Paint, and draft-related breeds, aged 0.5-23 years, were treated with periodic acid-Schiff (PAS) stain for glycogen and were immunostained to detect ubiquitin expression. On the basis of findings in PAS-stained sections, a diagnosis of equine polysaccharide storage myopathy (EPSSM) was made in 22 horses aged 2-23 years (mean, 9.4 years); samples from 6 horses aged 0.5-15 years (mean, 7.3 years) had a normal PAS staining pattern, with no relevant lesions. Ubiquitin expression was detected in all ...
Jose-Cunilleras E, Hinchcliff KW, Lacombe VA, Sams RA, Kohn CW, Taylor LE, Devor ST.Fatiguing exercise substantially decreases muscle glycogen concentration in horses, impairing athletic performance in subsequent exercise bouts. Our objective was to determine the effect of ingestion of starch-rich meals after exercise on whole body glucose kinetics and muscle glycogen replenishment. In a randomized, cross-over study seven horses with exercise-induced muscle glycogen depletion were either not fed for 8 h, fed half of the daily energy requirements ( approximately 15 Mcal DE) as hay, or fed an isocaloric amount of corn 15 min and 4 h after exercise. Starch-rich meals fed after e...
Kumar P, Timoney JF.The tonsil of the soft palate was an oval, flat structure located centro-rostrally on the oral surface of the soft palate. Its stratified squamous non-keratinized epithelium was perforated by holes or small crypts the deeper parts of which were loosely spongiform inter-digitated with lymphoid tissue. These unusual features have not previously been reported in tonsils of any species. Crypts and reticulated epithelium as found in the lingual and palatine tonsils were not observed. Lectins showed varying affinities for specific layers of the epithelium. M cells were not observed. A few Langerhans...
Valentine BA, Cooper BJ.Muscle samples were obtained at necropsy from 225 horses and ponies 1 year of age or older. Samples were processed in routine manner and were stained with hematoxylin and eosin and with periodic acid-Schiff for glycogen. Sections were examined for abnormal glycogen content and amylase-resistant complex polysaccharide and for chronic myopathic change (excessive fiber size variation, increase in number of internal nuclei). A total of 101 horses and ponies with lesions of polysaccharide storage myopathy were identified. Age of affected horses ranged from one to 30 years, with a mean of 14.7 years...
Yamano S, Eto D, Hiraga A, Miyata H.To consider the optimal training programme for Thoroughbred horses, we examined the recruitment pattern of muscle fibres including hybrid muscle fibres in well-trained Thoroughbred horses. The horses performed exercise at three different intensities and durations; i.e., 100% VO2max for 4 min, 80% and 60% VO2max for 8 min on a treadmill with 10% incline. Muscle samples were obtained from the middle gluteal muscle before, during (4 min at 80% and 60% VO2max), and after exercise. Four muscle fibre types (types I, IIA, IIA/IIX, and IIX) were immunohistochemically identified, and optical density of...
Collinder E, Nyberg F, Sanderson-Nydahl K, Gottlieb-Vedi M, Lindholm A.The opioid neuropeptide haemorphin-7 was measured, by immunoreactivity, in Standardbred horses during low-speed (7 m/s) and high-speed (10 m/s) endurance exercises, lasting 49-58 and 12-16 min respectively. In parallel, heart rate, muscle temperature and plasma lactate concentrations were measured. The profile of the low-speed exercise showed significantly increased heart rate after 10 min [154 beats per minute (bpm)]. After the exercise, muscle temperature (42.1 degrees C) and plasma lactate (4.8 mmol/l) were significantly increased. The profile of the high-speed exercise was comparatively ch...
Jose-Cunilleras E, Hayes KA, Toribio RE, Mathes LE, Hinchcliff KW.To clone and sequence cDNA for equine insulin-responsive glucose transporter (glucose transporter type 4 [GLUT-4]) and determine effects of glycogen-depleting exercise and meal type after exercise on GLUT-4 gene expression in skeletal muscle of horses. Methods: Muscle biopsy specimens from 7 healthy adult horses. Methods: Total RNA was extracted from specimens, and GLUT-4 cDNA was synthesized and sequenced. Horses were exercised on 3 consecutive days. On the third day of exercise, for 8 hours after exercise, horses were either not fed, fed half of daily energy requirements as hay, or fed an is...
Ribeiro WP, Valberg SJ, Pagan JD, Gustavsson BE.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,...
Annandale EJ, Valberg SJ, Mickelson JR, Seaquist ER.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...
Lacombe VA, Hinchcliff KW, Kohn CW, Devor ST, Taylor LE.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...
Ward TL, Valberg SJ, Lear TL, Guérin G, Milenkovic D, Swinburne JE, Binns MM, Raudsepp T, Skow L, Chowdhary BP, Mickelson JR.Comparative biochemical and histopathological data suggest that a deficiency in the glycogen branching enzyme (GBE) is responsible for a fatal neonatal disease in Quarter Horse foals that closely resembles human glycogen storage disease type IV (GSD IV). Identification of DNA markers closely linked to the equine GBE1 gene would assist us in determining whether a mutation in this gene leads to the GSD IV-like condition. FISH using BAC clones as probes assigned the equine GBE1 gene to a marker deficient region of ECA26q12-->q13. Four other genes, ROBO2, ROBO1, POU1F1, and HTR1F, that flank GB...
Lacombe VA, Hinchcliff KW, Devor ST.To characterize insulin-sensitive glucose-transporter (GLUT-4) protein in equine tissues and determine effects of exercise and glucose administration on content of GLUT-4 protein in equine skeletal muscle. Methods: Tissue samples from 9 horses. Methods: Western blot analyses were performed on crude membrane preparations of equine tissues to characterize GLUT-4. In a crossover, randomized study, horses were strenuously exercised for 3 consecutive days and then administered 13.5% glucose or isotonic saline (0.9% NaCl; control) solution, i.v., at similar infusion rates for 12.1 hours. Samples wer...
Nout YS, Hinchcliff KW, Jose-Cunilleras E, Dearth LR, Sivko GS, DeWille JW.To determine the effect of a single bout of exercise and increased substrate availability after exercise on gene expression and content of the glucose transporter-4 (GLUT-4) protein in equine skeletal muscle. Methods: 6 healthy adult Thoroughbreds. Methods: The study was designed in a balanced, randomized, 3-way crossover fashion. During 2 trials, horses were exercised at 45% of their maximal rate of oxygen consumption for 60 minutes after which 1 group received water (10 mL/kg), and the other group received glucose (2 g/kg, 20% solution) by nasogastric intubation. During 1 trial, horses stood...
McGowan CM, Golland LC, Evans DL, Hodgson DR, Rose RJ.Thirteen Standardbred horses trained intensively for 34 weeks and detrained for 12 weeks to investigate the effects of training, overtraining and detraining on muscle metabolites, buffering capacity and enzyme activities (CS, HAD and LDH). After a standardised exercise test to fatigue at 10 m/s (approximately 100% VO2max), there was significant depletion of [ATP], [PCr] and muscle [glycogen] and accumulation of muscle and plasma [lactate], [NH3] and elevated muscle temperature. After training, associated with increased run time to fatigue (148%), there was reduced depletion of muscle [glycogen...
Bröjer J, Jonasson R, Schuback K, Essén-Gustavsson B.The purpose was to investigate the degradation of proglycogen and macroglycogen in skeletal muscle during intense exercise. Ten Standardbred trotters performed a maximal treadmill exercise test comprising a warm-up period, an exercise period, starting at 7 m/s with increments of 1 m/s every 60 s until the onset of fatigue (mean +/- s.d. 246 +/- 32 s) and a walking recovery period. Muscle biopsies were taken at rest, immediately after exercise and 15 min postexercise. The exercise caused a marked anaerobic metabolism as shown by the decrease in both muscle ATP and creatine phosphate and increas...
Jansson A, Nyman S, Lindholm A, Lindberg JE.Studies of the effect of varying dietary carbohydrate compositions on exercise metabolism of horses are scarce. In the present study, the starch and sugar proportions were altered in the diet to 4 Standardbred horses. In a crossover experiment, the horses were offered a hay and oat diet, where the oats were substituted for barley syrup (BS) at 4 levels (BS 0, 0.5, 1.0 and 1.5 kg). Each diet was consumed for 21 days and both an incremental treadmill exercise test (IE) and a 40 min submaximal exercise test (SE) were performed. During the IE there was a significant (P<0.05) increase in mean VO...
Essén-Gustavsson B, Jensen-Waern M.Glycogenolysis and lipolysis are essential for energy production in muscle during prolonged exercise but less is known about the role of amino acid metabolism. The aim was to study the effect of an endurance race on pro- and macroglycogen, triglycerides and amino acid concentrations in muscle and on selected blood parameters, especially the amino acid response in the blood during the recovery phase. Seven endurance-trained horses completed a race covering 100-120 km. Blood samples were collected one day before the race, after the finish and 1 and 8 days after the race. Needle biopsy specimens ...
Rivero JL, Sporleder HP, Quiroz-Rothe E, Vervuert I, Coenen M, Harmeyer J.The purpose of this study was to determine whether oral L-carnitine supplementation enhances the responses of skeletal muscle to training in seven 2-year-old Standardbreds. Four horses were supplemented with 10 g/day L-carnitine for 10 weeks and 3 horses served as controls. All horses were exercised regularly every second day on a treadmill for 5 weeks (training period) and housed in individual boxes for 5 additional weeks (detraining period). The training period consisted of 8 high- and 8 low-speed exercises carried out in alternating sequence. Gluteus medius muscle biopsies were taken at Wee...
Essén-Gustavsson B, Karlström K, Lindholm A.Venous blood samples and middle gluteal muscle biopsies were obtained from 21 horses taking part in 100 km or 50 km endurance rides. Group A consisted of seven horses competing over 100 km (four horses completed the ride). Group B consisted of the six horses that were among the 10 best over 50 km while the other eight horses of Group C completed 50 km at a slower speed. Blood lactate, glycerol and creatine kinase increased in all groups while aspartate aminotransferase levels were higher only in Group A. No changes was found in blood glucose in Groups B and C while horses in Group A had lower ...
Waller AP, Heigenhauser GJ, Geor RJ, Spriet LL, Lindinger MI.We hypothesized that postexercise rehydration using a hypotonic electrolyte solution will increase the rate of recovery of whole body hydration, and that this is associated with increased muscle glycogen and electrolyte recovery in horses. Gluteus medius biopsies and jugular venous blood were sampled from six exercise-conditioned Standardbreds on two separate occasions, at rest and for 24 h following a competitive exercise test (CET) designed to simulate the speed and endurance test of a 3-day event. After the CETs, horses were given water ad libitum, and either a hypotonic commercial electrol...
Schuback K, Essén-Gustavsson B, Persson SG.The aim was to study metabolic response and locomotion pattern in Standardbred trotters during incremental treadmill exercise performed by increasing speed by 1 m/s in 1 min steps (start 7 m/s) until the onset of fatigue. The test protocol included determination of oxygen uptake, heart rate (HR), stride length (SL) and stride frequency (SF). Venous blood samples were collected at rest, at the end of each exercise step and after 30 min of recovery. Muscle biopsies were taken at rest and post exercise and muscle temperature was measured after exercise. As horses fatigued at different speed steps...
Rivero JL, Sporleder HP, Quiroz-Rothe E, Vervuert I, Coenen M, Harmeyer J.The purpose of this study was to determine whether oral L-carnitine supplementation enhances the responses of skeletal muscle to training in seven 2-year-old Standardbreds. Four horses were supplemented with 10 g/day L-carnitine for 10 weeks and 3 horses served as controls. All horses were exercised regularly every second day on a treadmill for 5 weeks (training period) and housed in individual boxes for 5 additional weeks (detraining period). The training period consisted of 8 high- and 8 low-speed exercises carried out in alternating sequence. Gluteus medius muscle biopsies were taken at Wee...
Gim JA, Ayarpadikannan S, Eo J, Kwon YJ, Choi Y, Lee HK, Park KD, Yang YM, Cho BW, Kim HS.Physical exercise induces gene expression changes that trigger glucose metabolism pathways in organisms. In the present study, we monitored the expression levels of LDHA (lactate dehydrogenase) and GYS1 (glycogen synthase 1) in the blood, to confirm the roles of these genes in exercise physiology. LDHA and GYS1 are related to glucose metabolism and fatigue recovery, and these processes could elicit economically important traits in racehorses. We collected blood samples from three retired thoroughbred racehorses, pre-exercise and immediately after 30 min of exercise. We extracted total RNA and ...
Tiley HA, Geor RJ, McCutcheon LJ.To determine the effects of dexamethasone treatment on selected components of insulin signaling and glucose metabolism in skeletal muscle obtained from horses before and after administration of a euglycemic-hyperinsulinemic clamp (EHC). Methods: 6 adult Standardbreds. Methods: In a balanced crossover study, horses received either dexamethasone (0.08 mg/kg, IV, q 48 h) or an equivalent volume of saline (0.9% NaCl) solution, IV, for 21 days. A 2-hour EHC was administered for measurement of insulin sensitivity 1 day after treatment. Muscle biopsy specimens obtained before and after the EHC were a...
Kelso TB, Hodgson DR, Visscher AR, Gollnick PD.Several biochemical components of the white portion of the gastrocnemius (WGM), plantaris (PM), and soleus (SM) muscles of the rat and middle gluteal (MGM) muscle of the horse were compared based on wet and dry weight, protein, and total creatine concentrations ([TCr]). The water content was similar for the rat hindlimb muscles, however, the concentrations of protein, ATP, phosphocreatine (PCr), creatine, and glycogen ranked as SM less than PM less than WGM for all reference bases except total creatine. In contrast, concentrations of ATP, creatine, and PCr were similar in all muscles studied w...
Nout YS, Hinchcliff KW, Jose-Cunilleras E, Dearth LR, Sivko GS, DeWille JW.To determine the effect of a single bout of exercise and increased substrate availability after exercise on gene expression and content of the glucose transporter-4 (GLUT-4) protein in equine skeletal muscle. Methods: 6 healthy adult Thoroughbreds. Methods: The study was designed in a balanced, randomized, 3-way crossover fashion. During 2 trials, horses were exercised at 45% of their maximal rate of oxygen consumption for 60 minutes after which 1 group received water (10 mL/kg), and the other group received glucose (2 g/kg, 20% solution) by nasogastric intubation. During 1 trial, horses stood...
Wagner ML, Valberg SJ, Ames EG, Bauer MM, Wiseman JA, Penedo MC, Kinde H, Abbitt B, Mickelson JR.Glycogen Branching Enzyme Deficiency (GBED), a fatal condition recently identified in fetuses and neonatal foals of the Quarter Horse and Paint Horse lineages, is caused by a nonsense mutation in codon 34 of the GBE1 gene, which prevents the synthesis of a functional GBE protein and severely disrupts glycogen metabolism. The aims of this project were to determine the mutant GBE1 allele frequency in random samples from the major relevant horse breeds, as well as the frequency with which GBED is associated with abortion and early neonatal death using the tissue archives from veterinary diagnosti...
Valberg S, Gustavsson BE, Lindholm A, Persson SG.Eight standardbred horses trotted on a treadmill for 55 mins at a sub-maximal speed of 5m/sec and subsequently performed an exercise test consisting of 2 min intervals at increasing speed. Heart (HR) and respiratory (Rf) rates and venous blood samples were obtained before, during and for 5 mins after exercise. Gluteus medius muscle biopsies and rectal temperatures were taken before and after exercise. The mean HR was 132/min and the mean Rf was 156/min during the 5m/sec trotting. With 5m/sec exercise, plasma free fatty acids (FFA), glucose, creatinine and cortisol concentrations increased mark...
Nostell KE, Essén-Gustavsson B, Bröjer JT.The branched chain amino acid leucine is a potent stimulator of insulin secretion. Used in combination with glucose it can increase the insulin response and the post exercise re-synthesis of glycogen in man. Decreased plasma amino acid concentrations have been reported after intravenous or per oral administration of leucine in man as well as after a single per oral dose in horses. In man, a negative correlation between the insulin response and the concentrations of isoleucine, valine and methionine have been shown but results from horses are lacking. This study aims to determine the effect of ...
Meng S, Zhang Y, Lv S, Zhang Z, Liu X, Jiang L.With their enormous muscle mass and athletic ability, horses are well-positioned as model organisms for understanding muscle metabolism. There are two different types of horse breeds-Guanzhong (GZ) horses, an athletic breed with a larger body height (~148.7 cm), and the Ningqiang pony (NQ) horses, a lower height breed generally used for ornamental purposes-both inhabited in the same region of China with obvious differences in muscle content. The main objective of this study was to evaluate the breed-specific mechanisms controlling muscle metabolism. In this study, we observed muscle glycogen, ...
Bröjer J, Holm S, Jonasson R, Hedenström U, Essén-Gustavsson B.The degradation of glycogen and its two forms, proglycogen (PG) and macroglycogen (MG) has been studied in horses performing different types of exercise, but no information is available about the resynthesis of PG and MG after exercise. Objective: To determine the resynthesis of PG and MG in skeletal muscle after intermittent uphill exercise. Methods: At a training camp 9 well-trained Standardbred trotters performed a training session comprising a warm-up period, 7 repeated 500 m bouts of exercise on an uphill slope and a recovery period. Muscle biopsies (m. gluteus medius) for analysis of PG,...
Hambleton PL, Slade LM, Hamar DW, Kienholz EW, Lewis LD.Four isocaloric diets containing 4, 8, 12 and 16% dietary fat (as soybean oil) were fed to four horses at four intervals according to a Latin square design. After 3 weeks of conditioning at each interval, diet effects were evaluated by trotting all horses at 3.2 m/sec for 6 hours. Pre- and posttrotting responses were measured in muscle and liver glycogen, serum long-chain fatty acids, serum electrolytes, serum enzymes, serum cholesterol, plasma glucose, packed cell volume and hemoglobin. Dietary fat was highly correlated with exercise-induced plasma glucose changes and with cholesterol concent...
Hodgson DR, Rose RJ, DiMauro J, Allen JR.The effects of training on skeletal muscle composition were studied in four Standardbred geldings given a seven week submaximal treadmill training programme. Before the start of training, muscle biopsies were collected from the left middle gluteal muscle for the determination of muscle fibre types, oxidative capacity and capillary numbers using histochemical techniques. The concentrations of citrate synthase, 3-hydroxyacyl-CoA dehydrogenase (HAD), lactate dehydrogenase and total muscle glycogen were measured using fluorometric methods. Muscle biopsy samples were repeated after one, three, five...
McKenzie EC, Eyrich LV, Payton ME, Valberg SJ.A previous report suggests a substantial incidence of exertional rhabdomyolysis (ER) in Arabian horses performing endurance racing. This study compared formalin histopathology and clinical and metabolic responses to a standardised field exercise test (SET) between Arabians with and without ER. Arabian horses with (n = 10; age 15.4 ± 5.6 years) and without (n = 9; 12.9 ± 6.1 years) prior ER were stall-rested for 24-48 h, after which paired ER and control horses were fitted with a telemetric ECG and performed a 47 min submaximal SET. Plasma glucose, lactate, electrolyte and...
Quiroz-Rothe E, Rivero JL.Combined methodologies of immunohistochemistry, histochemistry and photometric image analysis were applied: (1) to characterise control equine skeletal muscle fibres according to their myosin heavy chain (MyHC) composition and (2) to determine on a fibre-to-fibre basis the correlation between contractile [i.e. MyHC(s), myofibrillar ATPase (mATPase) and sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) isoforms], metabolic [i.e. succinate dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (GPD) activities, glycogen and phospholamban (PLB) contents], and morphological [i.e. cross-sect...
Yamano S, Eto D, Hiraga A, Miyata H.To consider the optimal training programme for Thoroughbred horses, we examined the recruitment pattern of muscle fibres including hybrid muscle fibres in well-trained Thoroughbred horses. The horses performed exercise at three different intensities and durations; i.e., 100% VO2max for 4 min, 80% and 60% VO2max for 8 min on a treadmill with 10% incline. Muscle samples were obtained from the middle gluteal muscle before, during (4 min at 80% and 60% VO2max), and after exercise. Four muscle fibre types (types I, IIA, IIA/IIX, and IIX) were immunohistochemically identified, and optical density of...
Bramer SA, Macedo A, Klein C.Secretion of histotroph during the prolonged pre-implantation phase in mares is crucial to pregnancy maintenance, manifested as increased embryonic loss in mares with age-related endometrial degeneration. Glycogen content of uterine histotroph is higher during the progesterone-dominated phase of the estrous cycle in mares, but regulatory mechanisms are not well understood. Methods: mRNA expression of glycogen-metabolizing enzymes (HK1, HK2, GSK3B, GYS1, PEPCK, PKM, PYGM) in endometrial samples were compared among mares in anestrus, estrus, and at Day 12 of diestrus and pregnancy. In addition, ...
Suagee JK, Corl BA, Swyers KL, Smith TL, Flinn CD, Geor RJ.High glycaemic feeds are associated with the development of insulin resistance in horses. However, studies that evaluated the effect of high glycaemic feeds used horses that either ranged in body condition from lean to obese or were fed to increase body condition over a period of months; thus, the ability of high glycaemic feeds to induce insulin resistance in lean horses has not been determined. This study evaluated the insulin sensitivity of 18 lean horses fed a 10% (LO; n = 6), 20% (MED; n = 6) or 60% (HI; n = 6) non-structural carbohydrate complementary feed for 90 days. Alth...
Ringmark S, Revold T, Jansson A.This study examined feed intake, growth, body condition, muscle glycogen content and nutrition-related health in 16 Standardbred horses fed a high-energy, forage-only diet ad libitum and allocated to either a control training programme (C-group) or a training programme with the high-intensity training distance reduced by 30% (R-group), from January as 2-year olds until December as 3-year olds. Feed intake was recorded on 10 occasions during 3 consecutive days. Body weight was recorded once in a week and height, body condition score (BCS), rump fat thickness and thickness of the m. longissimus ...
Reeta Pösö A, Hyyppä S.To test whether, in horses, the concentration of muscle glycogen can be influenced by increasing the uptake of glucose into the muscle cells or by providing a gluconeogenic precursor, 9 trained half-bred riding horses performed on a treadmill a 1.5 h competition exercise test (CET). Each horse performed CET 3 times and 30 min after CET, each was given one of the following solutions: isotonic glucose-electrolyte (GE) solution, GE supplemented with 50 g leucine (GEL) to increase insulin secretion, or GE supplemented with 200 ml propionic acid (GEP), a gluconeogenic precursor. Administration of G...
Valentine BA, Cooper BJ.Muscle samples from 24 horses with polysaccharide storage myopathy were stained with periodic acid-Schiff (PAS) stain and were immunostained for ubiquitin. Abnormalities detected with PAS stain were coarse granular cytoplasmic aggregates of amylase sensitive glycogen, subsarcolemmal aggregates of glycogen, central amylase sensitive bodies, and a variety of subsarcolemmal to intracytoplasmic amylase resistant polyglucosan inclusions. All amylase resistant inclusions were positive for ubiquitin. Ubiquitin was also detected in many amylase sensitive inclusions. Based on morphologic findings and p...
Valberg SJ, Townsend D, Mickelson JR.To determine whether polysaccharide storage myopathy (PSSM) in Quarter Horses is attributable to a defect in glycolysis or in the allosteric regulation of phosphofructokinase (PFK) enzyme. Methods: Muscle biopsy specimens were obtained from 6 Quarter Horses with PSSM and 8 Quarter Horse or Thoroughbred control horses. Methods: Maximal activity of glycogenolytic and glycolytic enzymes was determined spectrophotometrically. Maximal activity of PFK was determined for each horse at pH 8.0, and at pH 7.0 when variable concentrations of the activators, fructose 6 phosphate, fructose 2,6 bisphosphate...
Snow DH, Mackenzie G.The effects of intermittent maximal exercise (galloping) before and after a 10 week training programme were studied in 6 horses. Determinations were carried out on venous blood for packed cell volume, total plasma protein, glucose, glycerol, free fatty acids, lactate, 11-hydroxycorticosteroids, blood gases and pH. There were marked changes associated with galloping and some of these could be modified with training. The major findings included (i) an elevated blood glucose, (ii) a large increase in glycerol, which was greatest at 30 min post-exercise and was higher following training, (iii) sma...
McCue ME, Valberg SJ.To estimate the prevalence of polysaccharide storage myopathy (PSSM) among Quarter Horses in the United States and evaluate possible relationships between muscle glycogen concentration, turnout time, and exercise level. Methods: Cross-sectional study. Methods: 164 overtly healthy Quarter Horses > 2 years old from 5 states. Methods: Horses with a history of exertional rhabdomyolysis or any other muscular disease were excluded. Muscle biopsy specimens were examined histologically for evidence of PSSM and were submitted for determination of muscle glycogen concentration. A diagnosis of PSSM wa...
Geor RJ, Hinchcliff KW, Sams RA.To examine the role of beta-adrenergic mechanisms in the regulation of endogenous glucose (Glu) production [rate of appearance (R(a))] and utilization [rate of disappearance (R(d))] and carbohydrate (CHO) metabolism, six horses completed consecutive 30-min bouts of exercise at approximately 30% (Lo) and approximately 60% (Hi) of estimated maximum O(2) uptake with (P) and without (C) prior administration of the beta-blocker propranolol (0.22 mg/kg iv). All horses completed exercise in C; exercise duration in P was 49.9 +/- 1.2 (SE) min. Plasma Glu was unchanged in C during Lo but increased prog...
