Comparative functional anatomy of hindlimb muscles and bones with reference to aquatic adaptation of the sea otter

Although the sea otter (Enhydra lutris) is a complete aquatic species, spending its entire life in the ocean, it has been considered morphologically to be a semi-aquatic animal. This study aimed to clarify the unique hindlimb morphology and functional adaptations of E. lutris in comparison to other Mustelidae species. We compared muscle mass and bone measurements of five Mustelidae species: the sea otter, Eurasian river otter (Lutra lutra), American mink (Neovison vison), Japanese weasel (Mustela itatsi) and Siberian weasel (M. sibirica). In comparison with the other 4 species, E. lutris possessed significantly larger gluteus, popliteus and peroneus muscles, but smaller adductor and ischiopubic muscles. The popliteus muscle may act as a medial rotator of the crus, and the peroneus muscle may act as an abductor of the fifth toe and/or the pronator of the foot. The bundles of the gluteus superficialis muscle of E. lutris were fused with those of the tensor fasciae latae muscle and gluteofemoralis muscles, and they may play a role in femur abduction. These results suggest that E. lutris uses the abducted femur, medially rotated crus, eversion of the ankle and abducted fifth digit or extended interdigital web as a powerful propulsion generator. Therefore, we conclude that E. lutris is a complete aquatic animal, possessing differences in the proportions of the hindlimb muscles compared with those in other semi-aquatic and terrestrial mustelids.     

Muscle fibre distribution in forelimb,hindlimb and trunk muscles in three bat species: The little Japanese horseshoe,greater horseshoe and Egyptian fruit

This study characterised muscle fibres in trunk, forelimb and hindlimb muscles of three bat species: little Japanese horseshoe (Rhinolophus cornutus), greater horseshoe (Rhinolophus ferrumequinum) and Egyptian fruit (Rousettus aegyptiacus). Twenty-seven muscles from trunk, forelimb and hindlimb were dissected, weighed and analysed by immunohistochemistry and sodium didecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and determined their cross-sectional areas (CSA). Results showed that Type IIa and Type IIa/x made the highest proportion of total muscle mass. Moderate proportion was formed by Type IIb. Type I and IIx appeared at very low levels in all bats. Type IIb was the only fibre type detected in patagial muscles in wing membrane of greater horseshoe while other fibre types were not observed. Type I muscle fibres were very few and appeared infrequently in fifteen muscles of Egyptian fruit and in only one muscle in each, greater horseshoe and little Japanese horseshoe. Type IIx was also detected in three muscles in greater horseshoe and only one muscle in Egyptian fruit but none in little Japanese horseshoe. The highest average CSA μm² was detected in Type IIb and values were 734.2μm² for LHB; 1537.9μm² for GHB and 1,720.9μm² for EFB. Lowest and undetermined values were observed for Type I and IIx. These data demonstrate that Type IIa, IIa/x and IIb form significant proportion of adult bat muscle mass and Type IIb is the largest fibre type. The distribution pattern is suggestive of specialised functions of the fibres in relation to orientation and speed of bats during flight.     

Induction of relative growth changes in the musculoskeletal system of the sheep by limb immobilisation

The function of the limbs of the sheep was modified to study growth changes in the musculoskeletal system. Seven lambs treated with one hindlimb bound to the body, with the hip fully flexed and the stifle and hock fully extended, were reared from the day after birth to about three months old, together with two untreated controls. The effects of this functional alteration were measured by dissecting and weighing components of the whole carcase, by histometry and electron microscopy of the semitendinosus muscles, and by measurements and ashing of the femurs and tibias. With the particular exception of the hip bone and the muscles extending the hip on the bound side, muscles and bones tended to be heavier on the contralateral side in the hindlimb and on the ipsilateral side in the forelimb. The semitendinosus muscle of the bound limb weighed nearly twice as much as that of the controls. The increase in mass was due to a proportionate enlargement of all the muscle components studied. There was, however, a significant increase in the number of myosine adenosine triphosphatase low reacting fibres, as a percentage of the regional fibre population, in the deeper part of the muscle. It was concluded that the enlargement of the semitendinosus muscle was due to stretch and that the histochemical changes were due to chronic nervous stimulation.     

Sexual dimorphism in jaw muscles of the Japanese sparrowhawk (Accipiter gularis)

Materials suitable for anatomical research of raptorial birds are rare. Bird‐eating raptors show distinct inter‐sexual differences in body size and parental roles. The large females catch larger prey and prepare small morsels to feed their young using their hooked beaks. Here, we investigated the architectural properties of different jaw muscles of the Japanese sparrowhawk (Accipiter gularis) and examined whether there is sexual dimorphism in their architectural design. The results showed that musculus depressor mandibulae, the opener of the lower jaw, was characterized by relatively long fascicle length, whereas musculus pterygoideus was characterized by its larger mass and physiological cross‐sectional area (PCSA) in both sexes. Females have the potential capacity to produce rapid and strong bites by their significantly longer fascicle length of M. depressor mandibulae and larger mass and PCSA of M. pterygoideus. For body size‐matched gender, jaw muscles of males had fibres of relatively longer length than females, enabling greater velocity and excursion. Architectural characteristics of jaw muscles, together with the absolute dimorphism (the fascicle length of M. depressor mandibulae, the muscle mass and PCSA of M. pterygoideus) and relative dimorphism in the muscle mass of M. pterygoideus, reflect dietary difference and asymmetric parental roles between the sexes.     

Gender differences in morphometric properties of muscle fibres measured on cross-sections of rat hindlimb muscles

The study was aimed at demonstrating gender differences in the numbers, diameters and cross-section areas of muscle fibres for three hindlimb skeletal muscles responsible for locomotion and maintenance of body posture: soleus, tibialis anterior and flexor digitorum brevis in rats. The experiments were performed on five 6-month-old male and female Wistar rats. In both genders, all studied muscles of the right and left hindlimbs were isolated from surrounding tissues and excised for further procedures. The muscle transverse cross-sections taken from the muscle mid-belly were analysed. Following staining of reticular fibres by silver impregnation, the numbers, diameters and cross-section areas of muscle fibres were determined from microscopic images of muscle sections. The body mass of male rats was 80% higher than that of females. In addition, the muscle mass and the cross-section area were 53-82 and 26-45% higher in males, respectively. The number of muscle fibres was 11-42% higher in males than in females whereas the fibre diameters were 7-29% higher in males. The most conspicuous differences between males and females were found with respect to tibialis anterior, whereas the smallest differences were evident in soleus. The present study revealed that the gender morphometric differences in the studied rat hindlimb muscles were mainly owing to differences in number and size of muscle fibres and that the difference in muscle mass could be explained mainly from higher number of muscle fibres in males and to smaller degree from their larger diameters.     

A comparative histochemical and morphometric study of canine skeletal muscle.

The purpose of this study was to determine whether there were differences in skeletal muscle properties in the hindlimb muscles of different types of dogs. Muscle samples were obtained from the gracilis, sartorius cranial head, sartorius caudal head and tibialis anterior muscles of mixed-breed and hound-type dogs and Beagles. Fiber type, fiber size and capillary morphometry determinations of each muscle from each dog were made from sections stained for myofibrillar ATPase activity. Individual animals were bilaterally symmetric for all measured variables. Fiber type, fiber size and capillary geometry varied between dogs of a given type and muscles within a given dog. There were no differences between dog types for fiber type or fiber size; significant variation in log(muscle)/log(body) mass ratios between dog types was observed for all muscles. The results indicate that for a given muscle, significant variation can occur in skeletal muscle characteristics between different types of dogs and that these differences can be independent of differences in exercise history.     

Effects of hypothyroidism on the skeletal muscle blood flow response to contractions

Hypothyroidism is associated with impaired blood flow to skeletal muscle under whole body exercise conditions. It is unclear whether poor cardiac and/or vascular function account for blunted muscle blood flow. Our experiment isolated a small group of hindlimb muscles and simulated exercise via tetanic contractions. We hypothesized that muscle blood flow would be attenuated in hypothyroid rats (HYPO) compared with euthyroid rats (EUT). Rats were made hypothyroid by mixing propylthiouracil in their drinking water (2.35 x 10-3 mol/l). Treatment efficacy was evidenced by lower serum T3 concentrations and resting heart rates in HYPO (both P<0.05). In the experimental preparation, isometric contractions of the lower right hindlimb muscles at a rate of 30 tetani/min were induced via sciatic nerve stimulation. Regional blood flows were determined by the radiolabelled microsphere method at three time points: rest, 2 min of contractions and 10 min of contractions. Muscle blood flow generally increased from rest ( approximately 5-10 ml/min per 100 g) through contractions for both groups. Further, blood flow during contractions did not differ between groups for any muscle (eg. red section of gastrocnemius muscle; EUT, 59.9 +/- 14.1; HYPO, 61.1 +/- 15.0; NS between groups). These findings indicate that hypothyroidism does not significantly impair skeletal muscle blood flow when only a small muscle mass is contracting. Our findings suggest that impaired blood flow under whole body exercise is accounted for by inadequate cardiac function rather than abnormal vascular function.     

Relationships between muscle growth potential,intramuscular fat content and different indicators of muscle fibre types in young Charolais bulls

Genetic selection in favor of muscle growth at the expense of fat should affect characteristics of muscles, and therefore beef quality. This study was conducted with two extreme groups of six animals selected among 64 Charolais young bulls ranked according to their genetic potential for muscle growth. Muscle characteristics were assessed in Rectus abdominis (RA, slow oxidative) and Semitendinosus (ST, fast glycolytic) muscles. Intramuscular fat content and proportions of myosin heavy chains I (slow) and IIA (fast oxido‐glycolytic) and certain indicators of oxidative metabolism (activities of citrate synthase (CS), isocitrate dehydrogenase and cytochrome‐c oxidase (COX); expression of H‐fatty acid binding protein (FABP)) were higher in RA than in ST muscle. Genetic selection for muscle growth reduced intramuscular fat content and the activities of some oxidative metabolism indicators (namely CS, COX only). The positive correlation between muscle triacylglycerol content and A‐FABP messenger RNA level (a marker of adipocyte differentiation) (r = 0.53, P < 0.05) suggests that A‐FABP may be a good marker of the ability of bovines to deposit intramuscular fat. In conclusion, the metabolic muscle characteristics which respond to the selection process in favor of muscle growth clearly differ from the muscle characteristics which allow muscle types to be differentiated.     

The Hindlimb Myology of Tyto alba (Tytonidae,Strigiformes, Aves)

This work is the first myological dissection performed in detail on the hindlimb of Tyto alba. Six specimens were dissected and their muscle masses were obtained. T. alba has the classical myological pattern present in other species of Strigiformes, such as a well‐developed m. flexor digitorum longus and the absence of the m. plantaris, flexor cruris lateralis and ambiens. Also, T. alba lacks the m. extensor propius digiti III, m. extensor propius digiti IV and m. lumbricalis, present in the Strigidae. Hindlimb muscle mass accounts for 14.13% of total body mass, which is within the range of values of both nocturnal (Strigiformes) and diurnal (Falconidae and Accipitridae) raptors. This study provides important information for future studies related to functional morphology and ecomorphology.     

Progressive resistance‐loaded voluntary wheel running increases hypertrophy and differentially affects muscle protein synthesis,ribosome biogenesis,and proteolytic markers in rat muscle

We examined if 6 weeks of progressive resistance‐loaded voluntary wheel running in rats induced plantaris, soleus, and/or gastrocnemius hypertrophy and/or affected markers of translational efficiency, ribosome biogenesis, and markers of proteolysis. For 6 weeks, 8 male Sprague‐Dawley rats (~9–10 weeks of age, ~300–325 g) rats were assigned to the progressive resistance‐loaded voluntary wheel running model (EX), and ten rats were not trained (SED). For EX rats, the wheel‐loading paradigm was as follows – days 1–7: free‐wheel resistance, days 8–15: wheel resistance set to 20%–25% body mass, days 16–24: 40% body mass, days 25–32: 60% body mass, days 33–42: 40% body mass. Following the intervention, muscles were analysed for markers of translational efficiency, ribosome biogenesis, and muscle proteolysis. Raw gastrocnemius mass (+13%, p < .01), relative (body mass‐corrected) gastrocnemius mass (+16%, p < .001), raw plantaris mass (+13%, p < .05), and relative plantaris mass (+15%, p < .01) were greater in EX vs. SED rats. In spite of gastrocnemius hypertrophy, EX animals presented a 54% decrease in basal muscle protein synthesis levels (p < .01), a 125% increase in pan 4EBP1 levels (p < .001) and a 31% decrease in pan eIF4E levels (p < .05). However, in relation to SED animals, EX animals presented a 70% increase in gastrocnemius c‐Myc protein levels (p < .05). Most markers of translational efficiency and ribosome biogenesis were not altered in the plantaris or soleus muscles of EX vs. SED animals. Gastrocnemius F‐box protein 32 and poly‐ubiquinated protein levels were approximately 150% and 200% greater in SED vs. EX rats (p < .001). These data suggest that the employed resistance training model increases hind limb muscle hypertrophy, and this may be mainly facilitated through reductions in skeletal muscle proteolysis, rather than alterations in ribosome biogenesis or translational efficiency.     

Pax‐3 and Pax‐7 Label Muscle Progenitor Cells During Myotomal Myogenesis in Coregonus lavaretus (Teleostei: Coregonidae)

In Coregonus lavaretus, prior the mesoderm segmentation, in cells adjacent to the notochord called adaxial cells MyoD and slow myosin heavy chain (MyHC‐slow) proteins were observed. After somite formation, adaxial cells migrate towards the lateral part of the myotome and form a layer of red muscles. Deeper cells differentiate into white muscle fibres. In situ hybridization using Pax‐3 molecular probe revealed, that after somitogenesis, Pax‐3 is expressed in a layer of cells superficial to the myotome resembling the “external cells” (found in many teleosts species) or dermomyotome described in Amniota. During later developmental stages Pax‐3 gene is expressed in cells in intermyotomal space and then in myoblasts between myotubes. In these cells Pax‐7 protein was also observed. Pax‐3/7 positive cells which have migrated into the myotomes differentiate into satellite cells/secondary myoblasts and participate in hypertrophic and hyperplastic growth of muscles.     

Muscle growth in wild and domestic ducks

1. Increases in weight of the M. pectoralis, M. iliotibialis lateralis and M. flexor cruris lateralis were measured in mallards, White Pekins, Muscovies and a Muscovy × White Pekin cross from hatching to 154 days of age. Growth with respect to age was analysed using the Janoschek growth curve. 2. The M. pectoralis was less developed at hatching than both leg muscles. Furthermore, it showed a slower growth to its final weight and a later age at maximum growth than both leg muscles. 3. Pekins exhibited a faster Pectoralis and Iliotibialis lateralis muscle growth than mallards and Muscovies. The latter attained greater weights than Pekins at later ages owing to a higher asymptote. The cross showed the fastest muscle growth. 4. With respect to body weight, the Pectoralis is characterised by isometry followed by strongly positive allometry. This multiphasic allometry implies that relative muscle weights should not be used and the value of the allometric exponent strongly depends on both the beginning and duration of the period of investigation. Leg muscles showed isometric to slightly negative, simple allometry.     

An Immunohistochemical Observations on the Oviduct of the Goat

The oviduct has an important role in regulating transport of gametes and fertilization. The main role in these functions has a smooth muscle cells and ciliated epithelium lining the oviduct. All functions are under the influence of hormonal and nervous system. The objective of this study was immunohistochemically to examine the following structures: lining epithelium, smooth muscle cells, elastic fibres and nerve fibres. For this purpose, the following antibodies were used: cytokeratin 18, S‐100 protein, acetylated α‐tubulin, smooth muscle actin, desmin and elastin. Ciliary and secretory cells of the lining epithelium were positive for cytokeratin 18 and S‐100 protein. Cilia and the basal body‐associated structures of ciliary cells were positive to acetylated α‐tubulin. Smooth muscle cells (SMC) in mucosa and of the muscular layer were positive for α‐smooth muscle actin (SMA) and desmin. High density of nerve fibres positively reacted to acetylated α‐tubulin and S100 protein was present in the mucosa, muscular layer and serosa. Elastic fibres positive for elastin form a dense network at the base of the mucosal folds and in the muscle layer. A dense network of these fibres is accompanying the blood vessels. It is supposed that together with smooth muscle cells they are involved in the transport of ovum and in blood flow regulation.     

Decrease in mass of slow and fast tenotomized muscles of guinea pigs: role of nerve impulses and neurogenic factors

The role of nerve impulses and neurogenic factors in the decrease in muscle mass following tenotomy was investigated in 30 adult (15 males, 15 females) guinea pigs. Unilateral tenotomy, neurectomy and simultaneous tenotomy and neurectomy of slow and fast hindlimb muscles were performed in 3 groups respectively. Each group comprised 10 guinea pigs. The unoperated hindlimb of each animal in each group served as control. The weight loss occurred in both slow and fast muscles but was greater in the slow soleus muscle as compared to the fast gastrocnemius muscle. In each muscle the weight loss was least in the tenotomized group. This was followed by the weight loss in the neurectomized group. The greatest weight loss was observed in the simultaneously tenotomized and neurectomized group. These observations agree with the suggestion of other workers that a possible neurogenic factor flowing from the nerves to the muscles was very significant in maintenance of muscle fibre stability. It indicated also that simultaneous neurectomy and tenotomy did not prevent degenerative changes in slow and fast muscles and that it was not nerve impulses reaching the tenotomized muscles that were responsible for degenerative changes observed but that other factors were responsible.     

Decrease in mass of slow and fast tenotomized muscles of guinea pigs: Role of nerve impulses and neurogenic factors

The role of nerve impulses and neurogenic factors in the decrease in muscle mass following tenotomy was investigated in 30 adult (15 males, 15 females) guinea pigs. Unilateral tenotomy, neurectomy and simultaneous tenotomy and neurectomy of slow and fast hindlimb muscles were performed in 3 groups respectively. Each group comprised 10 guinea pigs. The unoperated hindlimb of each animal in each group served as control. The weigyt loss occurred in both slow and fast muscles but was greater in the slow soleus muscle as compared to the fast gastrocnemius muscle. In each muscle the weight loss was least in the tenotomized group. This was followed by the weight loss in the neurectomized group. The greatest weight loss was observed in the simultaneously tenotomized and neurectomized group. These observations agree with the suggestion of other workers that a possible neurogenic factor flowing from the nerves to the muscles was very significant in maintenance of muscle fibre stability. It indicated also that simultaneous neurectomy and tenotomy did not prevent degenerative changes in slow and fast muscles and that it was not nerve impulses reaching the tenotomized muscles that were responsible for degenerative changes observed but that other factors were responsible.     

Influence of feeding a grass hay diet during the early stage of the fattening period on growth performance,carcass characteristics,and meat production in Japanese Black steers

The present study investigated the influence of feeding a large amount of grass hay to steers from the early to middle fattening period on growth, carcass characteristics, and meat characteristics. Steers were randomly divided into grass hay‐fed (GHF, n = 6) and concentrate‐fed (CF, n = 6) groups. The dressed weight of the GHF steers was lower than that of the CF steers, but the final body weight was not significantly different between the groups. The GHF steers had decreased subcutaneous fat and rib thickness compared with the CF steers. Lipid content, monounsaturated fatty acids, and drip loss in the muscles were lower in the GHF steers than in the CF steers. Furthermore, n‐3 polyunsaturated fatty acids were higher in the GHF steers compared with the CF steers. The GHF steers had lower body weight during the middle fattening stage, which may have occurred as a result of muscle growth suppression caused by increased Myostatin expression; an increase in daily gain during the finishing period may have occurred as a result of muscle growth activation caused by decreased Myostatin expression. Feeding steers a grass hay‐based diet during the early fattening period possibly maintains the quantitative productivity of beef similarly to feeding a concentrate‐based diet.     

Associations between physiotherapy findings and subsequent diagnosis of pelvic or hindlimb fracture in racing Thoroughbreds

Reasons for performing study: Physiotherapists who work in racehorse training yards routinely treat horses' backs and hindquarters and may be able to recognise signs that indicate the presence of (impending) pelvic or hindlimb fracture before it becomes catastrophic. Objective: To establish whether physiotherapy assessment findings in Thoroughbred racehorses referred for routine physiotherapy could be predictive of subsequent (within 30 days) pelvic or hindlimb fracture diagnosis. Methods: Retrospective veterinary and physiotherapy data from a cohort of Newmarket (UK) Thoroughbred racehorses, were used. A case‐control study compared physiotherapy assessment findings of racehorses with and without a subsequently diagnosed pelvic or hindlimb fracture. Uni‐ and multivariable logistic regression was used to investigate and quantify the strength of association between physiotherapy findings and subsequent fracture diagnosis. Statistical significance was set at P<0.05. Results: A total of 513 horses provided 14 fracture cases for analysis. Presence of pelvic bony asymmetry, muscle atrophy of the quarters, reduced reflex movements of dorsi‐ and/or ventroflexion and spasm or tenderness on palpation of the gluteal muscles were significantly associated with subsequent fracture diagnosis in univariable analysis. Multivariable analysis indicated that horses subsequently diagnosed with pelvic or hindlimb fracture were 11.1 times more likely to show pelvic bony asymmetry, 4.7 times more likely to display muscle atrophy of the quarters and 6.6 times more likely to have spasm or tenderness on palpation of the gluteal muscles than those that were not. Conclusions: Racehorses presented for physiotherapy that show pelvic bony asymmetry, muscle atrophy of the quarters and/or spasm or tenderness on palpation of the gluteal muscles should alert the physiotherapist to the potential presence of (impending) pelvic or hindlimb fracture. Potential relevance: Earlier detection of (impending) pelvic or hindlimb fracture in racing Thoroughbreds could reduce the incidence of catastrophic fractures.     

Caprine sex affects skeletal muscle profile and MRFs expression during postnatal development

The important roles of myogenic regulatory factors (MRFs) have been well addressed in the process of mammalian skeletal myogenesis, while limited research has been performed in small ruminants. Furthermore, the effects of gender on the development of skeletal muscle and MRFs expression remain unknown. In this study, we identified the caprine Myf5, Myf6, MyoD and myogenin genes and quantified their expressions at six different postnatal time points by real‐time RT‐PCR. The sex has a marked effect on the expression differences of Myf5, MyoD and myogenin in the five investigated skeletal muscles, while minor influence on the expression difference of Myf6 except for Semitendinosus and Quadriceps femoris tissues (P < 0.001). The histological sections of muscles revealed a constant increase of muscle fiber diameter with aging but non‐significant differences between genders. We provide novel evidence for MRFs expression in age‐ and gender‐dependent manners, which will contribute to prioritizing these genes as potential candidate genes for trait‐associated study and provide a foundation for understanding the molecular control of skeletal muscle growth in goat species.     

Muscle protein expression of pikeperches (Stizostedion lucioperca and S. volgense)

The purpose of the present study was to investigate the muscle protein expression in two pikeperches (Stizostedion lucioperca and S. volgense) through intra‐ and intermyomeric composition of white muscles. Using denaturing 10% sodium dodecylsulfate‐polyacrylamide gel electrophoresis, muscle protein expression was studied in relation to within‐ and between‐species morphological development, sex, maturity and age of pikeperches. Myosin, actin and troponin have a distinct role in the contraction and length tension of muscle fibers of these species. No obvious intramyomeric differences were found in the myosin heavy chain of both species. Myosin light chains (15–38 kDa) have different expression in different age groups. The muscle protein of the fingerling and adult S. lucioperca had high molecular weight (50 kDa) myosin in contrast to the other Percid species. The molecular weight of actins increased comparatively in low‐age‐group fish. ATP is stored in myosin and released to cause contraction when myosin comes in contact with actin of the experimental fish. Troponin regulates increasing concentration of light‐chain myosin in mature fish. Because troponin T has been implicated in the regulation of skeletal muscle kinetics, muscle contraction kinetics was predicted in different age groups. The muscle proteins of both sexes of these species have polymorphism in various age groups but have no difference in similar aged fish. No muscle protein dimorphism was found in these Percid species. The white muscle protein composition and contractile properties affect power production during fast, unsteady movement and swimming.     

Muscle type‐specific effect of myostatin deficiency on myogenic regulatory factor expression in adult double‐muscled Japanese Shorthorn cattle

To clarify muscle type‐specific effect of myostatin on myogenic regulatory factors (MRFs), we examined mRNA expression of MRFs in five skeletal muscles of normal (NM) and myostatin‐deficient double‐muscled (DM) adult Japanese Shorthorn cattle by quantitative reverse‐transcribed PCR. Among the four MRFs, namely, Myf5, MyoD, myogenin, and MRF4, MyoD expression was different among the muscles of the DM cattle (P < 0.01) but not of the NM cattle. Meanwhile, MyoD expression was significantly elevated only in masseter (MS) muscle in the DM cattle due to the myostatin deficiency (P < 0.05). Myf5 and MRF4 expression in semitendinosus (ST) was higher in the DM than in the NM cattle (P < 0.05). According to analysis of myosin heavy chain (MyHC) isoform expression, more MyHC‐2x and ‐2a and less ‐slow isoforms were expressed in the longissimus and ST muscles compared to the MS muscle in both cattle (P < 0.05), but no significant difference in MyHC expression was observed between the NM and DM cattle. Taken together, myostatin has influences on Myf5 and MRF4 expression in faster‐type muscles and on MyoD expression in slower‐type muscles, suggesting a possible muscle type‐specific effect of myostatin in skeletal muscle growth and maintenance.