Muscle glycogen depletion patterns during draught work in Standardbred horses

Muscle fibre recruitment was investigated during draught loaded exercise by studying glycogen depletion patterns from histochemical stains of muscle biopsies from the gluteus and semitendinosus muscles. Three Standardbred trotters performed several intervals of draught loaded exercise on a treadmill with 34 kp at a trot (7 m/sec) and with 34 and 80 kp, respectively at a walk (2m/sec). Exercise was continued until the horses were unwilling to continue. Glycogen depletion was seen in all three fibre types when trotting with 34 kp for 5 or 10 mins. When an equal weight resistance was pulled at a walk, glycogen depletion was first seen in type I fibres only, then followed by a small percentage of type IIA fibres after at least 1 h. When 80 kp was pulled at a walk both type I and IIA fibres showed glycogen depletion, and after at least 30 mins exercise a small percentage of type IIB fibres was also depleted. These results indicate that the muscle fibres are depleted, in order, from type I through IIA to IIB as the intensity or duration of draught work increases.     

Histochemical staining characteristics of normal horse skeletal muscle

The histologic and histochemical staining characteristics of the triceps brachii (long head), extensor carpi radialis, gluteus medius, vastus lateralis, biceps femoris, semimembranosus, semitendinosus, and extensor digitorum longus muscles of 8 Thoroughbreds, 2 Quarter Horses, 1 Arabian, 1 Paso Fino, and 1 Shetland Pony are described. Muscle fiber morphology, staining distribution and intensity, amount of IM connective tissue, number of IM blood vessels and IM nerves, calcium-activated adenosine triphosphatase activity (CaATPase), percentage of fibertype population, percentage of relative fibertype area, mean fiber diameter, nonspecific esterase activity, alkaline phosphatase activity, and acid phosphatase activity were evaluated, using 10 common histochemical and histologic stains. Two fiber types (I, II) and 3 subtypes (IIA, IIB, IIC) were observed, using CaATPase-, nicotinamide-adenine dinucleotide-tetrazolium reductase-, periodic acid-Schiff hematoxylin-, and nonspecific esterase-stained frozen serial muscle sections. Type I muscle fibers in general had low CaATPase activity, high oxidative capacity, low glycogen capacity, and low esterase activity. Type IIA muscle fibers had high CaATPase activity, intermediate oxidative capacity, high glycogen concentration, and high esterase activity. Type IIB fibers had high CaATPase activity, low oxidative capacity, high glycogen concentration, and a high esterase activity. Type IIC muscle fibers had high CaATPase activity, high oxidative capacity, variable glycogen concentration, and high esterase activity. Type II (IIA and IIB) muscle fibers predominated in the muscles. The percentage of muscle fiber population, mean minimal muscle fiber diameter, and percentage of relative muscle fiber area were determined for each sampled muscle. Type IIA and IIB muscle fibers predominated in the percentage of muscle fiber population and percentage of relative muscle fiber area. Type IIB muscle fibers had the greatest minimal fiber diameter, type IIA muscle fibers had intermediate minimal fiber diameter, and type I muscle fibers had the smallest minimal fiber diameter. The percentage of relative muscle fiber area was less variable (P less than or equal to 0.05) than the percentage of muscle fiber population. Mean muscle fiber diameter did not significantly differ between breeds. Alkaline and acid phosphatase activities were at low levels in all muscles biopsied and were limited to the IM connective tissue fibrocytes, macrophages, and capillaries.(ABSTRACT TRUNCATED AT 400 WORDS)     

Changes in fibre type composition of gluteus medius and semitendinosus muscles of Dutch Warmblood foals and the effect of exercise during the first year postpartum

In order to obtain broader insights into the equine musculoskeletal system, we studied the fibre type composition of 2 locomotory muscles in biopsies from Dutch Warmblood foals taken at 3 different ages in the first year postpartum. The muscle fibre types were determined histochemically as well as immunohistochemically. ATPase-characterised IIB fibres appear to express either IId or type lIa plus IId myosin heavy chain (MHC). A high percentage of fibres classified as IIA with ATPase expressed both fast types of MHC. The type I classification by the 2 methods matched almost completely. There was an increase with age of fibres expressing I and IIa MHC in the gluteus medius. At the same time, there was a decrease of fibres expressing IId MHC and fibres co-expressing MHC IIa and IId. MHC expression of the semitendinosus muscle did not change over time at first, but from age 22-48 weeks there was a decrease in the percentage of type IId fibres. In general, the gluteus medius contained more type I fibres but fewer type IId fibres compared to the semitendinosus. At most ages the fibre type compositions of both muscles correlated with one another. To examine the effect of exercise, one-third of the foals were given box rest, one-third received training and one-third kept at pasture during the first 22 weeks of life. The 3 exercise groups differed in their fibre type composition; however, these differences could not be attributed to the effect of exercise.     

Type,diameter and distribution of fibres in some respiratory and abdominal muscles of the goat

This study was designed to determine the histochemical properties, size and composition of fibres in the diaphragm, intercostal and abdominal muscles of goats to clarify whether reported similarities in respiratory muscle physiology between goats and humans have a structural basis. Serial sections (10 µm) of muscular tissue from adult female goats were stained for myosin adenosine triphosphatase and reduced nicotinamide adenine dinucleotide dehydrogenase-tetrazolium reductase activities; the fibres were classified into types I, IIA and IIB; and their mean diameter and composition were determined. Abdominal and intercostal muscles contained types I, IIA and IIB fibres in the ratio 1:1:1, and the mean diameter of the fibres ranged from 49.2 to 62.2 µm. In contrast, the diaphragm contained 58.9% type I and 41.1% type II fibres, and the latter could not be differentiated into types IIA and IIB. Diaphragmatic fibres were also smaller (36.9 – 40.9 µm). These findings contrast with those in humans, where the diaphragm, intercostal and abdominal muscles contain >50% type I fibres and have fibres of identical diameter. The differences in fibre characteristics between the diaphragm, intercostal and abdominal muscles of goats and the differences between goats and humans need to be taken into consideration in interpreting the results from studies in respiratory muscle physiology.Abbreviations mATPase myosin adenosine triphosphatase - NADH-TR nicotinamide adenine dinucleotide dehydrogenase-tetrazolium reductase     

Muscle fibre characteristics of active and inactive standardbred horses

Muscle biopsies were taken from the middle gluteus muscle of 36 Standardbred horses. Twelve of the horses were inactive, while 24 were actively trained and raced. Twelve of the trained horses were moderate performers, with a mean racing time of 1 min 21 secs per km (741 m/min) and the other 12 were excellent performers, with a mean racing time of 1 min 16 secs per km (789 m/min). The percentage and mean area of Type I fibres were similar in all three groups of horses. Marked differences were found among the subgroups of Type II fibres. The well-trained horses had a higher proportion of Type IIA fibres and a lower proportion of the Type IIB (58 per cent IIA and 15 per cent IIB fibres in the excellent performers; 49 per cent IIA and 26 per cent IIB in the moderate performers) than the inactive horses (41 per cent IIA and 35 per cent IIB fibres). The mean area of Type II fibres was smaller in the muscle of the active horses (excellent performers: IIA, 3075 micron2; IIB, 3378 micron2) moderate performers: IIA, 3185 micron2; IIB, 4252 micron2) than in that of the inactive ones (IIA, 3714 micron2; IIB, 5935 micron2). Intramuscular substrates (glycogen and triglycerides) and the activities of enzymes used as markers for the glycolytic potential of the muscle seemed to be similar in the three groups of horses, although there were large interindividual variation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Oxidative capacity of skeletal muscle fibres in racehorses: histochemical versus biochemical analysis

The oxidative capacity of skeletal muscle fibre types was evaluated histochemically using the nicotinamide dinucleotide diaphorase (NADH-D) staining, and biochemically by measuring the activity of citrate synthase (CS) in both whole muscle samples and in pools of fibres of identified type. Duplicate determinations of the NADH-D staining pattern resulted in standard deviations (sd) between duplicates of 6 and 11 per cent for two observers. The NADH-D pattern was found to differ between observers. Duplicate determinations of CS activity in the same fibre pools resulted in an sd value of 2.9 mumol/g/min. Measurements of whole muscle CS activity did not provide information about the distribution of oxidative capacity among fibre types. The NADH-D stain and CS activity in fibre pools both showed that, in general, type I and IIA fibres had a higher oxidative capacity than type IIB fibres. Biochemical techniques also showed, however, that the CS activity in type I and IIA fibres of different horses could vary as much as twofold, whereas the NADH-D rating showed a high intensity staining for most type I and IIA fibres in all horses. Furthermore, type IIB fibres received a lower NADH-D rating than the other fibre types even when the CS activities were quite similar. For purposes of research, biochemical measurement of oxidative capacity in individual muscle fibre types provides valuable quantitative and comparative information. The ease of histochemical NADH-D staining in comparison to fibre dissections makes this technique more practical for routine estimates of the distribution of oxidative capacity among muscle fibres.(ABSTRACT TRUNCATED AT 250 WORDS)     

Skeletal muscle fibre characteristics in young and old bulls and metabolic response after a bullfight

Fibre type composition, activities of enzymes such as citrate synthase (CS), 3-hydroxyacyl coenzyme A dehydrogenase (HAD), lactate dehydrogenase (LDH), as well as glycogen, lactate and pH levels were analysed in muscle biopsies (m. gluteus medius) obtained after bullfighting from 10 young and 10 old bulls. No changes were seen in fibre type composition between groups, but the older bulls had higher HAD and LDH activities. Low glycogen concentrations and low pH values were found in both groups, but the lactate concentration after bullfighting was higher in the older group of bulls. The histochemical stain for glycogen revealed that type IIB fibres in both young and old bulls contained more glycogen than seen in type IIA and type I fibres. These results show that young and old bulls have similar muscle fibre type composition, but the metabolic capacity differs, with a higher glycolytic capacity and lactate production in older bulls. Furthermore, it seems that the physical and emotional stress in connection with a bullfight causes a marked depletion of glycogen, especially of type I and IIA fibres.     

Muscle responses of thoroughbreds to conventional race training and detraining

Ten healthy sedentary Thoroughbreds with previous race training experience were trained conventionally for 9 weeks. Muscle biopsy samples were obtained before and after training and after 6 weeks of detraining pasture rest. Biopsy samples were obtained from the right deltoid, triceps, vastus lateralis, middle gluteal, biceps femoris, and semitendinosus muscles. The deep-frozen biopsy samples were analyzed for activities of succinate dehydrogenase (SDH), 3-hydroxy-acylcoenzyme A dehydrogenase (HAD), and phosphorylase (PHOS) and for glycogen concentration. The triceps and gluteal muscle samples were also serially sectioned and stained for myofibrillar actomyosin adenosine triphosphatase (ATPase) activity after alkaline (pH 10.3) and sequential acidic (pH 4.34) ATPase inactivation. Fiber types I (alkaline preincubation), IIA1, IIA2, and IIA3 (sequential acidic preincubation over 5 minutes) were identified and were evaluated for fiber-type distribution and fiber areas. Increases in response to training were observed in deltoid and vastus muscle SDH and gluteal muscle HAD activities, and deltoid muscle glycogen concentration (P less than 0.05 to P less than 0.01). Changes in PHOS activity were not observed. Type-IIA1, -IIA2, and -IIA3 fiber areas in triceps muscle were increased in response to training (P less than 0.05 to P less than 0.01). Changes in fiber-type distribution did not occur in response to training. Changes in muscle enzyme activities, glycogen concentration, fiber types, and fiber areas were not seen from posttraining to detraining. Further increases were observed when detraining values were compared with pretraining values in deltoid, triceps, vastus, gluteal, and biceps femoris muscle SDH activities and in gluteal muscle glycogen concentration (P less than 0.05 to P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of developmental changes in the coexpression of myosin heavy chains and metabolic properties of equine skeletal muscle fibers

OBJECTIVE: To determine the growth-related changes in metabolic and anatomic properties in equine muscle fiber type, including hybrid fibers identified with immunohistochemical analysis. ANIMALS: 24 2-, 6-, 12-, and 24-month-old female Thoroughbreds. PROCEDURE: Samples were obtained from the gluteus medius muscle of all horses. Expression of myosin heavy chain (MHC) isoforms MHC-I, -IIa, -IIb, and -IIx in each muscle fiber was detected by use of 4 primary monoclonal antibodies: BA-D5, SC-71, BF-F3, and BF-35, respectively. Five muscle fiber types (types I, I/IIA, IIA, IIA/IIX, and IIX) were immunohistochemically identified. The area and activity of succinic dehydrogenase (SDH) in each fiber type were determined by use of quantitative histochemical staining and image analysis. RESULTS: Although the proportion of type I and IIX fibers did not change with age, the proportion of type IIA and IIA/IIX fibers significantly increased and decreased, respectively, from 2 months to 24 months of age. The increase in proportion of type IIA fibers with growth may have been attributable to muscle fiber-type transition from type IIA/IIX fibers but not from type IIX fibers. Values for SDH activity and fiber area in hybrid fiber types were intermediate to those for their respective pure phenotypes. CONCLUSIONS AND CLINICAL RELEVANCE: Hybrid fibers have an important role for determining the proportion of muscle fiber type in horses < 24 months old, and the metabolic and anatomic properties of the hybrid fibers are well coordinated, as in mature horses.     

Muscle fibre type composition in untrained and endurance-trained Andalusian and Arab horses

Muscle biopsies were taken from the middle gluteal muscle of 68 stallions (52 Andalusian [AN] and 16 Arab [AR]) ranging from six to 12 years of age. Seventeen AN horses and eight AR horses were untrained, while the remainder underwent active endurance training for 6 months. Fifteen AN horses were moderately endurance-trained while the other 20 AN horses and eight AR horses were strongly endurance-trained. Percentages of type I and type II fibres were similar in all groups (P greater than 0.05). The group of horses with the hardest training had a higher percentage of type IIA fibres (AN P less than 0.01; AR P less than 0.02) and a lower percentage of type IIB fibres (P less than 0.05 for AN and AR) than the untrained horses. All trained horses had a higher percentage of type IIB oxidative fibres and a lower percentage of type IIB non-oxidative fibres than the untrained horses (P less than 0.01 for both). These results suggest that the proportions of type I and type II fibres are highly stable within a given breed, but the stimulus of training facilitates changes both in contractile properties and, particularly, in the oxidative capacity of type II subgroups.     

Age-related changes in percentage of fiber types and mean fiber diameters of the ovine quadriceps muscles.

Mean fiber diameters and percentages of each fiber type of the vastus lateralis, vastus medialis, rectus femoris, and vastus intermedius muscles from 15 sheep, ranging from 1 day to 5 years of age, were determined. Myosin adenosine triphosphatase and nicotinamide adenine dinucleotide-tetrazolium reductase stained sections were used. The vastus lateralis, vastus medialis, and rectus femoris contained 3 fiber types (I, IIA, and IIB). The vastus intermedius was composed almost entirely of type I fibers. From birth to 5 years of age, mean fiber diameters of type I fibers increased from 15.8 to 47.0 micron in the vastus lateralis, 15.6 to 50.7 micron in the vastus medialis, 17.5 to 46.5 micron in the rectus femoris, and 26.7 to 51.8 micron in the vastus intermedius. Means of fiber diameters of type II fibers increased from 16.1 to 44.6 micron in the vastus lateralis, 19.8 to 44.0 micron in the vastus medialis, and 17.0 to 44.5 micron in the rectus femoris. The percentage of type II fibers in the vastus lateralis, vastus medialis, and rectus femoris decreased from 85% to 90% at birth to approximately 72% at 5 years of age. The vastus intermedius consisted of only type I fibers in sheep 2 years and older.     

Neuronal nitric oxide synthase is heterogeneously distributed in equine myofibers and highly expressed in endurance trained horses

Mammalian skeletal muscle expresses splice variants of neuronal nitric oxide synthase (nNOS). Skeletal muscles have a metabolically heterogeneous population of myofibers, and fiber composition in equine skeletal muscle is correlated with athletic ability in endurance events. In this study, we investigated whether nNOS expression in equine skeletal muscle is related to fiber type and endurance training. Biopsy samples obtained from the gluteus medius of sedentary- (SH) and endurance-trained (TH) horses were examined for the electrophoretic mobility of myosin heavy chain (MHC) and NOS activity. Serial tissue cross-sections were stained for myosin ATPase and nicotinamide adenine dinucleotide (NADH) reductase, and also immunostained for nNOS. The gluteus medius of TH had higher levels of nNOS expression and activity when compared to muscle from SH. In SH, nNOS was restricted to the subsarcolemmal area while in TH nNOS was also present at cytoplasmic sites. A splice variant of nNOS was heterogeneously distributed among the different myofibers, its expression being higher in fast-oxidative-glycolytic type IIA fibers than in fast-glycolytic type IIX fibers and absent in slow-twitch type I fibers. Trained horses had a significantly higher relative content of type IIA fibers, a greater oxidative capacity, and a lower percentage of type IIX fibers when compared with SH. The differences in muscle fiber typing between the 2 groups of horses reflected alterations that probably resulted from the endurance-training program. Overall, these results show that nNOS is differentially expressed and localized in the gluteus medius according to the fiber type and the athletic conditioning of the horses.     

Enzyme histochemistry on muscle biopsies as an aid in the diagnosis of diseases of the equine neuromuscular system: a study of six cases

Muscle biopsies from six horses with clinical histories of muscle atrophy, muscle tremors, myopathic symptoms, unsteadiness of pelvic limbs and progressive ataxia were examined. Muscle biopsies were studied with enzyme histochemical techniques to evaluate the diagnostic values of these methods in cases suspected of suffering from neuromuscular disorders. Hypertrophy, atrophy, fibre splitting, waxy degeneration, phagocytosis and necrosis were seen in haematoxylin eosin stained sections of the different cases. Fibre type predominance and fibre type grouping were seen in the calcium ion stimulated myosine ATP-ase (Ca-ATP-ase) stained sections of some cases. 'Moth-eaten fibres' were demonstrated in three cases by staining with NADH: nitro blue tetrazolium oxidoreductase (NADH-TR), succinate dehydrogenase (SDH), NADH dependent malate dehydrogenase, cytochrome c oxidase and by lactate dehydrogenase. The catabolic enzymes, acid phosphatase (ACP) and 5'-nucleotidase were active in cases with fibre phagocytosis. The oxidative part of the pentose phosphate pathway in myopathic tissue seemed to be important in three cases, demonstrated by the increased activity of glucose-6-phosphate dehydrogenase (GPDH) and 6-phosphogluconate dehydrogenase (PGDH). The important feature of diseased horse muscle was that the pathohistochemical changes were exactly the same as in diseased skeletal muscles of humans. The application of tissue saving enzyme histochemical techniques can be recommended in the study of muscle tissue from horses suffering from suspected neuromuscular disorders.     

Enzyme histochemical features of equine gluteus muscle fibers

Gluteal muscle specimens were taken from 4 horses. From 1 of the 4 gluteal muscles, serial sections were prepared. Individual muscle fibers were identified and studied, using photomicrographs of sections stained by different enzyme histochemical methods. In specimens in which cytoplasmic soluble enzymes were studied, use was made of the semi-permeable membrane technique to hamper enzyme diffusion into reaction fluids. Enzymes involved in glycogenolysis, glycolysis, the tricarboxylic acid cycle, synthesis of reduced nicotinamide adenine dinucleotide phosphate, the pentose phosphate cycle, the alpha-glycerolphosphate shuttle, the respiratory chain, catabolism, and muscular contraction were studied. Some key enzymes of different metabolic pathways were also included. Each of 3 fiber types identified had distinct features. Type I fibers were characterized by a relatively strong aerobic capacity, compared with type IIA fibers, which were more glycolytic and had strong aerobic and moderate-to-strong anaerobic capacity. Type IIB fibers were characterized by a relatively low aerobic and a relatively high anaerobic capacity, and were glycolytic. Activities of phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase, lactate dehydrogenase, and alpha-naphtylesterase (nonspecific esterase) were so markedly different in the 3 fiber types that fiber typing was possible, aided by the demonstration of the activities of these enzymes. In type IIB fibers, the pentose phosphate cycle was more important than in the other fiber types. Except for the unexplained high alpha-naphtylesterase activity in type IIB fibers, catabolic enzymes were not active in healthy equine muscle fibers.     

The effect of testosterone on gastrocnemius muscle fibres in growing and adult male and female rats: a histochemical,morphometric and ultrastructural study

In this study, the effect of testosterone on gastrocnemius muscle fibres in growing and adult rats (male and female) was examined using histochemical, morphometric and ultrastructural techniques. After physiological saline (PS), olive oil (OvO) or olive oil + testosterone (OvOT) injections on 72 rats (growing and mature, 36 male and 36 female), the sample tissues of fibre types of the gastrocnemius muscle taken were examined by histochemical [alkaline adenosine triphosphatase (alk-ATPase), acid ATPase (ac-ATPase)], morphometric and ultrastructural techniques. In PS-injected control groups, the gastrocnemius muscle of both sexes contained all the fibre types studied [slow-oxidative muscle fibres (type I), fast-oxidative glycolytic muscle fibres (type IIA) and fast-glycolytic muscle fibres (type IIB)]. The type I fibres had the smallest diameter, type IIA had a medium diameter and type IIB fibres had the largest diameter. In OvO-injected groups, it was observed that the OvO had little effect on the gastrocnemius muscles of either sex, although there was significant enlargement of type IIB fibres. After the injection of OvOT, hypertrophy of muscle fibres was determined by morphometric study. The biggest increase in diameter was on type I fibres. In addition, degenerations on some mitochondria, accumulation of lipid droplets on type I and type II fibres, an increase in glycogen particles, bifurcation of myofibrils, an increase in the number and diameter of units resembling T tubules and an increase in ribosomal content were also observed in the same group by transmission electron microscope. Consequently, it was determined that testosterone can induce protein synthesis in gastrocnemius muscle fibres, and induces changes in shape and size, and also can change the appearance and the number of fibres.     

Histochemical differentiation of fiber types in neonatal canine skeletal muscle

Differentiation of fiber types in developing canine skeletal muscle was studied, using morphologic, morphometric, and histochemical techniques. Sample collections were made from 6 muscles from the pectoral and pelvic limbs of 16 healthy pups between 1 day and 12 weeks of age. In newborn pups, 90% to 95% of the fibers in the 6 muscles were classified as undifferentiated or type IIC; the remaining fibers were classified either normal or large-size type I. Large-size type I fibers usually accounted for 2% to 4% of the total population and were considered analogous with the B fiber of Wohlfart. These fibers were larger than all other fiber types and disappeared after pups reached 4 to 5 weeks of age. After 2 to 4 weeks, the number of undifferentiated fibers decreased with the appearance of, and the concomitant numerical increases of, normal size type I and type IIA fibers. The percentages of type I and IIA fibers approached proportions of the adult dog by 12 weeks, at which time a type IIA fiber predominance was present in biceps femoris, lateral head of the gastrocnemius, cranial tibial, and long head of the triceps. Type I fibers predominated in medial head of the triceps and superficial digital flexor after 4 to 5 weeks. The mean fiber diameters of type I and IIA fibers were similar to any given muscle throughout the postnatal development. All fiber types stained uniformly with the oxidative stain nicotinamide adeninedinucleotide-tetrazolium reductase during the first 12 weeks of life, whereas a distinction between type I and II fibers was evident after 3 to 4 weeks with the periodic acid-Schiff stain reaction.     

Comparison of the histological and histochemical properties of skeletal muscles between carbon dioxide and electrically stunned chickens

1. Histological and histochemical profiles of Musculus pectoralis (PT, type IIB fibres), M. iliotibialis lateralis (ITL, types IIA + IIB fibres) and M. puboischiofemoralis pars medialis (PIF, type I fibres) were compared in carbon dioxide (37%, 70 s) and electrically (14 V, 5 s) stunned male chickens. 2. Muscle materials were taken at 0, 4 and 24 h from carcases dressed and cooled with ice-water mixture for 30 min. Glycogen and fat contents, and adenosine triphosphatase and reduced nicotinamide adenine dinucleotide dehydrogenase activities of fibres were measured. 3. In PT muscle at 0 h, gas stunned chickens showed many fibres with high glycogen content but those electrically stunned contained few such fibres. Fibres from gas stunned birds had lost almost all their glycogen after 24 h of cold storage. 4. In the ITL muscle of gas stunned chickens at 0 h residual glycogen was observed in type IIB fibres. In contrast, in the electrically stunned birds it was in type IIA, showing the different effects of the stunning methods. During cold storage, glycogen disappeared earlier in type IIB than IIA fibres. 5. In PIF muscle with fibres of low glycogen content, the gas stunned chickens maintained a good fibre structure for 4 h or more, but the electrically stunned had already lost intact fibre structure at 4 h. 6. These results indicated that the carbon dioxide stunning was a better method for chicken welfare and meat quality than electrical stunning.     

Glycogen depletion patterns in horses performing maximal exercise

Muscle biopsy samples were collected from the left middle gluteal muscle of horses participating in competitive barrier trials. Twelve horses were biopsied the day before and within 30 minutes of completion of an 800 m barrier trial. A further six horses were sampled the day before, and within 30 minutes of, completion of a 1200 m barrier trial. Serial muscle sections were examined histochemically for myosin adenosine triphosphatase activity after acid preincubation, to demonstrate type I, IIA and IIB fibres. The glycogen content in the individual fibres was assessed using the periodic acid Schiff (PAS) reaction. Total glycogen in muscle was measured fluorimetrically after hydrolysis to glucose. Significant decreases in total muscle glycogen levels of 167.1 +/- 22.2 and 158.1 +/- 23.2 mmoles glucose units kg-1 (dry weight) (mean +/- standard error) occurred from pre- to post trial samples for horses in both 800 and 1200 m trials respectively. There were no significant differences between the decreases in total muscle glycogen from horses in either 800 m or 1200 m trials. In both 800 m and 1200 m trials there was a significant decrease in the percentage of type IIA and IIB fibres classified as having high PAS staining intensity, and a significant increase in the percentage of fibres classified as having medium staining intensity when samples taken after the trial were compared to those taken before the trial.     

Energy metabolism in relation to skeletal muscle fibre properties during treadmill exercise

The skeletal muscle metabolism of horses with a wide range of cardiocirculatory capacities was studied during a standardised near-maximal exercise test in relation to muscle fibre composition. Although the same amount of work was performed by all horses the amount of triglycerides and glycogen utilised and lactate accumulated differed widely. Both blood and muscle lactate accumulation were positively related to the amount of glycogen utilised. These factors were in turn positively associated with the percentage of Type IIB fibres and consequently negatively associated with the percentage of Type IIA fibres. The percentage of Type IIB fibres was negatively correlated to the activities of the oxidative enzymes citrate synthase and 3-hydroxyacyl-CoA-dehydrogenase and positively associated with the lactate dehydrogenase activity. The results indicate that the horses with a high proportion of Type IIB fibres had a lower muscle oxidative capacity and were, therefore, for energy production, more dependent upon glycolysis with subsequent lactate accumulation than horses which had a high proportion of Type IIA fibres. The different metabolic properties of the muscle fibre types indicate that the pattern of muscle fibre recruitment could have a significant effect on intramuscular substrate utilisation.