Histochemical properties of muscle fibres types and enzyme activities in skeletal muscles of Standardbred trotters of different ages

Fibre characteristics and enzyme activities were determined for the gluteus, semitendinosus, vastus lateralis and triceps brachii muscles of 55 Standardbred trotters of different ages. Four fibre types (I, IIA, IIB, IIC) were demonstrated by histochemical staining of myofibrillar adenosine triphosphatase after preincubation at different pH values. Type II fibres predominated in all the muscles and the type IIA/IIB ratio was higher in horses over 5 years than in younger horses, except in the vastus in which the IIA/IIB ratio did not change with age. The vastus had the highest proportion of type IIA fibres and the semitendinosus the highest proportion of type IIB fibres. Histochemical demonstration of NADH dehydrogenase disclosed that almost 100 per cent of the type IIA and many of the type I and IIB fibres were medium-stained; the remaining type I fibres were darkly stained and the type IIB fibres lightly stained. In older horses more fibres were stained for NADH dehydrogenase. The activity of triosephosphate dehydrogenase decreased that that of 3-hydroxy-acyl-coA dehydrogenase and citrate synthase increased in all the muscles except the vastus with increasing age. The greatest increase in oxidative capacity occurred in the gluteus and triceps. Training, rather than age, was regarded as the factor inducing these changes. The results emphasise that histochemical data are only semiquantitative, and there are apparent discrepancies in the intensities of histochemical staining and the biochemical evaluation of various enzymes.     

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.     

Muscle characteristics and plasma lactate and ammonia response after racing in Standardbred trotters: relation to performance

Blood samples from the jugular vein and muscle biopsies (gluteus medius) in 25 Standardbred trotters were obtained 5-10 min after racing. The biopsies were analysed for fibre type composition and enzymatic profile and blood samples for plasma lactate and ammonia concentrations. Muscle characteristics, plasma lactate and ammonia concentrations after racing were compared with each horse's individual performance index (IPI). The IPI is calculated annually from the individual horse's racing performance (% placing 1, 2 or 3, total annual earnings, average earning per start, and best racing record), respectively, converted to and expressed as a percentage deviation from the average record of the same sex and age group. The IPI values were 100-116. Plasma lactate concentrations were 15.0-42.7 mmol/l (mean 31.3 mmol/l) and ammonia concentrations 65-210 micromol/l (mean 141 micromol/l) after racing. Fibre type composition varied among horses (range 9-27% for Type I, 32-54% for Type IIA, and 27-46% for Type IIB). Fibre type composition, enzyme activities, plasma lactate and ammonia responses to racing were not correlated to IPI. Ten of the horses also performed a submaximal test on the track, consisting of 5 incremental 1000 m heats at approximate speeds of 9.1, 9.5, 10.0, 10.5, and 11.1 m/s. Immediately after each heat a blood sample was drawn from the jugular vein for plasma lactate analysis. Plasma lactate response to exercise differed between horses, but no correlation was seen with IPI. Muscle characteristics, plasma lactate and ammonia concentrations after racing and lactate response to a submaximal track test did not correlate with current race performance expressed as IPI in a group of horses with average or better performance capacity at the time of testing. Analysis of lactate and ammonia in blood after racing is not a valuable tool to predict an individual performance index.     

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)     

Metabolic response to racing and fiber properties of skeletal muscle in standardbred and thoroughbred horses

Muscle biopsies were obtained from 17 Standardbred trotters (S) and 22 Thoroughbred racehorses (T) after races which varied in length from 1200 to 2840 m. Biopsies were taken between 2 and 14 minutes from the conclusion of the race. Histochemical and biochemical analyses were performed on all muscle samples. Standardbred horses possessed fewer Type II fibers, especially Type IIB fibers, and demonstrated a higher oxidative and lower glycolytic capacity in muscle than Thoroughbred horses. Intramuscular glycogen and lac-tate concentrations were lower in Standardbred horses after racing (mean 420 and 82 mmol/kg d.w. respectively) com-pared to Thoroughbred horses (mean 545 and 148 mmol/kg d.w. respectively). Low levels of intramuscular adenosine triphosphate (ATP) (mean S 17, T 15 mmol/kg d.w.) and creatine phosphate (mean S 28, T 42 mmol/kg d.w.) were recorded in both breeds after racing. Differences in muscle enzyme activities and metabolic response to exercise between breeds were related to the different muscle fiber compositions of Standardbred and Thoroughbred horses. Within both breeds, a high percentage of Type IIB fibers was associated with a low oxidative and high glycolytic capacity in muscle and a greater lactate accumulation after racing. In Standardbred horses low intramuscular ATP concentrations post-race were associated with a high percentage of Type IIB fibers and high lactate levels. No relationship was found between placing or speed of racing and intramuscular lactate and ATP concentrations post-race. This may have been due to many other factors which affected the outcome of a race and also due to the fact that it was not known when during a race lactate accumulation and ATP depletion occurred. Since the properties of fiber types appeared to be very different, the metabolic response within individual fiber types may be more closely related to fatigue than the metabolic response measured in whole muscle.     

Skeletal muscle characteristics in young trained and untrained standardbred trotters.

Muscle biopsies were taken from the middle gluteal muscle of 28 Standardbred trotters, 3-4 years of age. The 13 horses in Group T were trained consistently from 18 months of age, whereas the 15 horses in Group UT were not exposed to any systematic training before 3 years of age. Group T horses had a lower percentage of Type IIB fibres (31%) than did Group UT horses (39%). Citrate synthase (CS) activity, representing oxidative capacity, was higher in Group T (72 mmol kg-1 min-1) than in Group UT (47 mmol kg-1 min-1). Biopsies were taken from 4 horses in each group when they were foals and then annually until 3-4 years of age. Results from this study indicate that regular training of Standardbreds from 18 months of age resulted in increased CS activity and a decrease in the percentage of Type IIB fibres. This study shows that training, not growth, is the main factor that induces a high oxidative capacity and a high Type IIA/IIB fibre ratio in muscle of Standardbred trotters.     

Glycogen depletion patterns in horses competing in day 2 of a three day event

Muscle biopsy samples were collected from the left middle gluteal muscle of the horses participating in day 2 (speed and endurance test) of a three day event. Six Thoroughbred horses were biopsied the day before and within 30 minutes of completion of the speed and endurance test. Serial muscle sections were reacted histochemically for myosin adenosine triphosphatase activity after acid pre-incubation to demonstrate Type I, IIA and IIB fibers and the glycogen content in the individual fibers was assessed using the periodic acid Schiff (PAS) reaction. Total glycogen in muscle was measured fluorometrically after hydrolysis to glucose. A significant decrease (P less than 0.001) in total muscle glycogen of 306.0 +/- 34.6 mmoles glucose units/kg (dry weight) (mean +/- SE) occurred when samples collected before exercise were compared to those collected following exercise. A significant decrease (P less than 0.05) in the percentage of Type I fibers having medium PAS staining intensity occurred when pre and post-exercise samples were compared. Significant decreases (P less than 0.01 and P less than 0.001 respectively) in the percentage of Type IIA and IIB fibers classified as having high PAS staining intensity occurred when post-exercise samples were compared with those pre-exercise. There were significant increases (P less than 0.01 and P less than 0.001 respectively) in the percentage of Type IIA and IIB fibers classified as having medium PAS staining intensity when the samples collected after the exercise were compared with those before the exercise.     

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.     

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.     

Fibre types,enzyme activities and substrate utilisation in skeletal muscles of horses competing in endurance rides

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 change was found in blood glucose in Groups B and C while horses in Group A had lower levels after the ride. Neither fibre composition, fibre areas nor enzyme activities differed between the groups. Intramuscular glycogen content was similar before the ride in all groups. After the ride glycogen had decreased only half as much in Group C as compared to Groups A and B. Group C had a higher intramuscular triglyceride content at rest than Group B. The greatest decrease in triglyceride content after the ride was found in Group C. In Groups A and B many Type I, IIA and IIB fibres were glycogen depleted after the ride while in Group C mainly Type I and some Type IIA fibres were depleted. The results of this study show that intramuscular carbohydrate and lipid stores are both important fuels during endurance rides.     

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.     

Recruitment pattern of muscle fibre type during high intensity exercise (60-100% VO2max) in thoroughbred horses

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 periodic acid Schiff staining (OD-PAS) in each fibre type, and the glycogen content of the muscle sample, were determined by quantitative histochemical and biochemical procedures. The changes in OD-PAS showed that the recruitment of all fibre types were identical at the final time stage of each exercise bout, i.e., 4 min running at 100% VO2max, and 8 min running at 80% and 60% VO2max. The changes in OD-PAS of type IIA/IIX fibre were very similar to those of type IIX fibre. The recruitment of these fibres were obviously more facilitated by 4 min running at 100% VO2max than by 4 min running at 80% or 60% VO2max. Short duration with high intensity exercise, such as 4 min running at 100% VO2max or 8 min running at 80% or 60% VO2max, is effective to stimulate type IIX fibre and IIA/IIX fibres that have the fastest speed of contraction.     

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)     

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.     

Training and growth induced changes in the middle gluteal muscle of young Standardbred trotters

The middle gluteal muscle of five, two-year-old untrained trotters was investigated by repeated needle biopsy sampling over a training period of six months. A second group of five, three-year-old untrained horses was included to examine the effect of growth. After the training period increases were found in the relative distribution of slow twitch (ST) fibres from 18 per cent to 25 per cent and fast twitch (FTa) fibres from 36 per cent to 45 per cent, and a decrease in FTb fibres from 46 per cent to 30 per cent. A proportionally equal reduction (approximately 18 per cent) in the cross sectional area of all fibre types was observed after the first two months of training succeeded by an increase to approximately pretraining levels at the end of the period. The number of capillaries per fibre was enhanced from 1.7 to 2.4. Proliferation of capillaries occurred around fibres of all types. The metabolic adaptations showed increases in the activities of 3-hydroxy-acyl-CoA dehydrogenase (HAD) (50 per cent) and citrate synthase (31 per cent). Growth had no effect on the relative fibre type distribution nor the capillary per fibre ratio, but as the mean fibre area increased 36 per cent (primarily because of increases in FT fibres) the number of capillaries/mm2 was lower in the older untrained horses (350 capillaries/mm2) compared with the younger untrained ones (460 capillaries/mm2). Increase with growth was found in the activity of phosphorylase and HAD and a decrease was seen in the activity of hexokinase. It is concluded that the training programme exclusively induced alterations which improved the aerobic capacity of the muscle.     

Age and exercise effects on mitochondrial density and capillary fibre ratio in bird leg muscle

1. Muscle fibre composition, capillary-fibre ratio and mitochondrial density of the Iliotibialis lateralis muscle were monitored during growth from the age of 8 weeks to sexual maturity (24 weeks) in sedentary birds and in birds subjected to regular treadmill exercise. 2. The Iliotibialis lateralis muscle consists almost exclusively of type IIA and IIB fibres with a small percentage of "unclassified" fibres. Over the 16-week period of growth there was no change in fibre composition but a marked fibre hypertrophy linked with a fall in the capillary-fibre ratio. Mitochondrial volume density increased with age but this was not significant. 3. Exercise significantly increased the IIA:IIB fibres ratio from 0.77 to 1.1 but had no significant effect on any other measured characteristics. 4. It is concluded that exercise at the intensity and duration employed (10-15 min daily, ca. 70-80% maximum oxygen consumption) has little effect on the growth and development of avian skeletal muscle although there was evidence of an increased oxidative capacity of the muscle.     

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     

Free Radical Formation after Intensive Exercise in Thoroughbred Skeletal Muscles

Although high oxygen consumption in skeletal muscle may result in severe oxidative stress, there are no direct studies that have documented free radical production in horse muscles after intensive exercise. To find a new parameter indicating the muscle adaptation state for the training of Thoroughbred horses, we examined free radical formation in the muscle by using electron paramagnetic resonance (EPR). Ten male Thoroughbred horses received conventional training for 18 weeks. Before and after the training period, all horses performed an exhaustive incremental load exercise on a 6% incline treadmill. Muscle samples of the middle gluteal muscle were taken pre-exercise and 1 min, 1 hr, and 1 day after exercise. Muscle fiber type composition was also determined in the pre-exercise samples by immunohistochemical staining with monoclonal antibody to myosin heavy chain. We measured the free radical in the muscle homogenate using EPR at room temperature, and the amount was expressed as relative EPR signal intensity. There was a significant increase in Type IIA muscle fiber composition and a decrease in Type IIX fiber composition after the training period. Before the training period, the mean value of the relative EPR signal intensity showed a significant increase over the pre-exercise value at 1 min after the exercise and an incomplete recovery at 24 hr after the exercise. While no significant changes were found in the relative EPR signal intensity after the training period. There was a significant relationship between percentages of Type IIA fiber and change rates in EPR signal intensity at 1 min after exercise. The measurement of free radicals may be useful for determining the muscle adaptation state in the training of Thoroughbred horses.     

Enzyme-Histochemical Profiles of Fiber Types in Mature Canine Appendicular Muscles

The histochemical characteristics of skeletal muscle were assessed using a range of samples from 7 appendicular muscles taken from adult mixed-breed dogs (1.5 to 3 years of age). Two slow-twitch fiber subtypes (IA and IB) and three II subtypes (IIA, IIB and IIC) were identified according to myofibrillar myosin adenosine triphosphatase reaction after acid and alkaline preincubation. Type IIB fibers were not found in all muscles, and were only biologically significant in m. semiten-dinosus. The metabolic potential of these fibers is fairly similar to that of IIA fibers, but significantly different to that of IIB fibers in other mammals, suggesting that they may be designed to play a different functional role during locomotion. All canine muscle fibers have moderate to high oxidative capacity, which may be related to the extraordinary athletic capability of the species.     

Intralesional injection of platelet-rich plasma followed by controlled exercise for treatment of midbody suspensory ligament desmitis in Standardbred racehorses

OBJECTIVE: To determine outcome of Standardbred racehorses with moderate to severe midbody suspensory ligament desmitis (MSD) treated by means of ultrasound-guided intralesional injection of a single dose of platelet-rich plasma (PRP) followed by a program of gradually increased exercise. DESIGN: Nonrandomized clinical trial. ANIMALS: 9 Standardbred racehorses. PROCEDURES: Following injection of PRP, horses were allowed a controlled, gradual return to exercise. Race records for the year prior to injury and for 3 consecutive years after horses returned to racing were reviewed. For comparison purposes, race records of 9 Standardbred racehorses with no history of MSD racing at the same time were also reviewed. RESULTS: All 9 horses with MSD returned to racing after treatment; median time to return to racing was 32 weeks. All 9 horses raced at least once during the first and second years after returning to racing, but only 5 raced during the third year. When number of starts, total earnings, and earnings per start were compared between case and comparison horses, the only significant differences were number of starts during the third year after case horses returned to racing and earnings per start during the first year after case horses returned to racing, with values being significantly lower for case horses than for comparison horses. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that horses with moderate to severe MSD treated by means of intralesional injection of a single dose of PRP followed by a program of gradually increased exercise had an excellent prognosis for returning to racing.