Arterial to end-tidal CO2 tension and alveolar dead space in halothane- or isoflurane-anesthetized ponies

The correlation between end-tidal partial pressure of CO2 (PETCO2) and arterial (PaCO2) was determined for spontaneously breathing ponies under halothane or isoflurane anesthesia. The PETCO2 was useful as a trend indicator of PaCO2 during the first 60 minutes of halothane or isoflurane anesthesia when PaCO2 values were less than 60 to 70 mm of Hg. Halothane anesthesia lasting greater than 90 minutes was associated with PaCO2 values in excess of 60 to 70 mm of Hg, a large arterial- to end-tidal PCO2 difference (PaCO2-PETCO2) and a significant increase in alveolar dead space. These effects were not seen during the same period of isoflurane anesthesia. Arterial blood gas analysis is therefore recommended during halothane anesthesia when the PETCO2 is greater than 60 to 70 mm of Hg. A decrease in alveolar capillary perfusion relative to alveolar ventilation is the most likely cause for the increase in alveolar dead space during halothane anesthesia. Based on these findings, isoflurane may be superior to halothane for prolonged anesthesia of spontaneously breathing horses.     

Systemic distribution of blood flow in ponies during 1.45%, 1.96%, and 2.39% end-tidal isoflurane-O2 anesthesia

Effects of 1.1, 1.5, and 1.8 minimal alveolar concentration (MAC) isoflurane-O2 (1.45%, 1.96%, and 2.39% end-tidal isoflurane, respectively) anesthesia on cardiac output, blood pressure, and blood flow to the brain, thyroid glands, adrenal glands, kidneys, and splanchnic organs were examined in 9 healthy isocapnic adult ponies. Tissue blood flows were studied using 15-micron diameter radionuclide-labeled microspheres that were injected into the left ventricle, and comparisons were made with data obtained from ponies in the conscious state. Isoflurane anesthesia caused dose-related reduction in cardiac output and arterial blood pressure, but total peripheral resistance was not significantly altered (P greater than 0.05). In the brain, vasodilation occurred with exposure to isoflurane that peaked at 1.5 MAC. Vasodilation was more pronounced in the cerebellum, pons, and medulla, compared with that in the cerebrum. Perfusion increased in cerebellar gray, as well as white, matter. However, in the cerebrum, blood flow increased in the white matter, whereas it decreased in caudate nuclei and was similar to value in the cortex of awake ponies. In thyroid glands and pancreas, intense vasoconstriction occurred during isoflurane anesthesia which caused precipitous reduction in blood flow in these organs. By contrast, adrenal gland blood flow was not affected during the 3 levels of isoflurane anesthesia because vasodilation occurred. The renal blood flow registered dose-dependent reductions during isoflurane-O2 anesthesia, but renal vasoconstriction occurred only during the deepest level (1.8 MAC) of anesthesia. Although the small intestine and and colon blood flow decreased with each concentration of isoflurane, the splenic blood flow remained unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of administration of isoflurane at approximately the minimum alveolar concentration on depression of a nociceptive withdrawal reflex evoked by transcutaneous electrical stimulation in ponies

OBJECTIVE: To investigate effects of isoflurane at approximately the minimum alveolar concentration (MAC) on the nociceptive withdrawal reflex (NWR) of the forelimb of ponies as a method for quantifying anesthetic potency. ANIMALS: 7 healthy adult Shetland ponies. PROCEDURE: Individual MAC (iMAC) for isoflurane was determined for each pony. Then, effects of isoflurane administered at 0.85, 0.95, and 1.05 iMAC on the NWR were assessed. At each concentration, the NWR threshold was defined electromyographically for the common digital extensor and deltoid muscles by stimulating the digital nerve; additional electrical stimulations (3, 5, 10, 20, 30, and 40 mA) were delivered, and the evoked activity was recorded and analyzed. After the end of anesthesia, the NWR threshold was assessed in standing ponies. RESULTS: Mean +/- SD MAC of isoflurane was 1.0 +/- 0.2%. The NWR thresholds for both muscles increased significantly in a concentration-dependent manner during anesthesia, whereas they decreased in awake ponies. Significantly higher thresholds were found for the deltoid muscle, compared with thresholds for the common digital extensor muscle, in anesthetized ponies. At each iMAC tested, amplitudes of the reflex responses from both muscles increased as stimulus intensities increased from 3 to 40 mA. A concentration-dependent depression of evoked reflexes with reduction in slopes of the stimulus-response functions was detected. CONCLUSIONS AND CLINICAL RELEVANCE: Anesthetic-induced changes in sensory-motor processing in ponies anesthetized with isoflurane at concentrations of approximately 1.0 MAC can be detected by assessment of NWR. This method will permit comparison of effects of inhaled anesthetics or anesthetic combinations on spinal processing in equids.     

Skeletal muscle blood flow in anaesthetized horses. Part II: effects of anaesthetics and vasoactive agents

OBJECTIVE: This review aims at evaluating studies investigating the effects of anaesthesia on skeletal muscle blood flow and associated cardiovascular function in anaesthetized horses and discusses how the results of these studies contribute to our understanding of the pathogenesis and prevention of post-anaesthetic myopathy. DATABASE USED: Pubmed & personal files. CONCLUSION: There is little published information on the effects of anaesthesia on skeletal muscle blood flow in horses. Available reports predominantly refer to halothane and isoflurane. The effects of vasoactive drugs have mainly been studied in halothane-anaesthetized horses. The results of these studies support the importance of cardiac output in the maintenance of adequate arterial blood pressure, perfusion pressure and muscle blood flow. Adequate perfusion pressure appears to be important for overcoming the detrimental effects of high intra-compartmental pressure in dependent muscles and hydrostatic pressure in nondependent muscles.     

Respiratory muscle perfusion in ponies during prolonged submaximal exercise in thermoneutral environment.

Distribution of blood flow among various respiratory muscles was examined in 8 healthy ponies during submaximal exercise lasting 30 minutes, using radionuclide labeled 15-microns diameter microspheres injected into the left ventricle. From the resting values (40 +/- 2 beats/min; 37.3 +/- 0.2 C), heart rate and pulmonary arterial blood temperature increased significantly at 5 (152 +/- 8 beats/min; 38.6 +/- 0.2 C), 15 (169 +/- 6 beats/min; 39.8 +/- 0.2 C), and 26 (186 +/- 8 beats/min; 40.8 +/- 0.2 C) minutes of exertion, and the ponies sweated profusely. Mean aortic pressure also increased progressively as exercise duration increased. Blood flow increased significantly with exercise in all respiratory muscles. Among inspiratory muscles, perfusion was greatest in the diaphragm and ventral serratus, compared with external intercostal, dorsal serratus, and scalenus muscles. Among expiratory muscles, blood flow in the internal abdominal oblique muscle was greatest, followed by that in internal intercostal and transverse thoracic muscles, in which the flow values remained similar. The remaining 3 abdominal muscles had similar blood flow, but these values were less than that in the internal intercostal, transverse thoracic, and internal abdominal oblique muscles. Blood flow values for all inspiratory and expiratory muscles remained similar for the 5 and 15 minutes of exertion. However, at 26 minutes, blood flow had increased further in the diaphragm, external intercostal, internal intercostal, transverse thoracic, and the external abdominal oblique muscle as vascular resistance decreased. On the basis of our findings, all respiratory muscles were activated during submaximal exercise and their perfusion had marked heterogeneity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiopulmonary function during 5 hours of constant-dose isoflurane in laterally recumbent, spontaneously breathing horses

Hemodynamic and respiratory effects of 5 h of unvarying 1.57%, end-tidal (1.2 MAC) isoflurane in O2 anesthesia were characterized in ten left laterally recumbent horses. Compared to base line values at 30 min of constant dose isoflurane, cardiac output, hematocrit, total plasma solids, PaCO2, and peak inspired gas flow progressively and significantly (P less than 0.05) increased over the course of study. Arterial blood pressure increased (P less than 0.05) during the first 2 h of constant dose of isoflurane then decreased and remained near base line values. Inspiratory time progressively decreased with time of anesthesia. All horses recovered from anesthesia uneventfully within 1 h of termination of isoflurane.     

Cardiovascular and respiratory measurements in awake and isoflurane-anesthetized horses

Circulatory and respiratory function was monitored in nonmedicated, spontaneously breathing horses (n = 7) immediately before, during, and 1 hour after 85 +/- 4.1 (X +/- SEM) minutes of constant 1.57% isoflurane in O2 anesthesia. Comparison of values during anesthesia with those obtained while horses were awake revealed a significant (P less than 0.05) decrease in arterial blood pressure that was related to a slight, but insignificant, decrease in cardiac output and peripheral vascular resistance. Although isoflurane anesthesia and recumbency resulted in a significant (P less than 0.05) decrease in stroke volume, cardiac output did not decrease significantly because heart rate tended to increase. Isoflurane and recumbency also significantly (P less than 0.05) increased PaCO2, peak expiratory gas flow, total expiratory time, and PCV and significantly decreased PaO2, minute expired ventilation, and the ratio of peak inspired to expired gas flow. Differences imposed by isoflurane anesthesia were reversed by 1.5 hour after anesthesia.     

Fiber type composition of rostral and caudal portions of the digastric muscle in the dog

The distribution of muscle fiber types in rostral and caudal portions of the musculus digastricus (digastric muscle) was studied in 6 dogs. Staining procedures which stain specifically for type IIM fibers, a fiber type found in other muscles supplied by the trigeminal nerve, were used. Rostral and caudal portions of the muscle were compared because the rostral portion is innervated by the trigeminal nerve, and the caudal portion is innervated by the facial nerve. The musculus triceps brachii (triceps muscle), which contains fiber types I and IIA, and the musculus masseter (masseter muscle), which contains type IIM, were used as controls. Mean fiber diameters were calculated for each of the muscles. Both portions of the digastric muscle exhibited the same histochemical behavior, possessing types I and IIA myofibers. Neither portion contained type IIM fibers. Type I fibers in the masseter muscle were histochemically different from type I fibers in the other muscles studied. Type II fibers predominated in all 3 muscles, but there were significantly (P less than 0.001) more type I fibers in the triceps muscle than in either portion of the digastric muscle or in the masseter muscle. Type II fibers were significantly larger than type I fibers in the caudal digastric (P less than 0.01) and masseter (P less than 0.05) muscles. There was no difference in the size of type I or type II fibers between any of the muscles studied (P greater than 0.20).     

The effects of isoflurane minimum alveolar concentration on withdrawal reflex activity evoked by repeated transcutaneous electrical stimulation in ponies

The aim of this study was to quantify the effects of isoflurane at approximately the minimum alveolar concentration (peri-MAC) on the temporal summation (TS) of reflex activity in ponies. TS was evoked by repeated electrical stimulations applied at 5 Hz for 2 s on the digital nerve of the left forelimb of seven ponies. Surface electromyographic activity was recorded from the deltoid and common digital extensor muscles. TS thresholds and amplitude of response to stimulations of increasing intensities were assessed during anaesthesia at 0.85, 0.95 and 1.05 times the individual MAC, and after anaesthesia in standing animals. Under isoflurane anaesthesia, TS thresholds increased significantly in a concentration-dependent fashion and at each isoflurane MAC, the responses increased significantly for increasing stimulation intensities. A concentration-dependent depression of evoked reflexes with a reduction in the slopes of the stimulus–response function was observed for both muscles. The results demonstrated that with this model it is possible to describe and quantify the effects of anaesthetics on spinal sensory-motor processing in ponies.     

Temporal effects of halothane and isoflurane in laterally recumbent ventilated male horses

Cardiopulmonary function was monitored in 6 non-medicated, healthy male horses, anesthetized with halothane or isoflurane in O2 at a constant dose (1.2 times the minimum alveolar concentration). Horses were exposed once to each anesthetic agent, and a minimum of 2 weeks separated anesthetic exposures. All horses were studied in left lateral recumbency, and ventilation was mechanically controlled to induce a PaCO2 of 35 to 45 mm of Hg and an inspiratory peak airway pressure of 18 to 22 cm of H2O. After 1 hour of horse preparation, constant conditions were begun. With duration of anesthesia, cardiac output increased (P less than 0.05) with both anesthetic agents, because of an increase in stroke volume (P less than 0.05). Heart rate did not change from initial values with either agent. Mean arterial blood pressure also increased (P less than 0.05) with both agents. With both anesthetics, respiratory rate (P less than 0.05) was increased progressively to maintain acceptable PaCO2 values. Arterial O2 tension did not change with time.     

Cerebral, renal, adrenal, intestinal, and pancreatic circulation in conscious ponies and during 1.0, 1.5, and 2.0 minimal alveolar concentrations of halothane-O2 anesthesia

Blood flow to the brain, kidneys, adrenal glands, pancreas, and small intestine was studied in 8 healthy ponies while awake (control) and during 1.0, 1.5, and 2.0 minimal alveolar concentrations (MAC) of anesthesia produced, using halothane vaporized in oxygen. During the anesthesia steps, intermittent positive-pressure ventilation was used to ensure isocapnia. Organ blood flow was determined with 15-micron (diameter) radionuclide-labeled microspheres, after allowing 30 minutes of equilibration at each of the 3 preestablished end-tidal halothane concentrations. The sequence of 1.0, 1.5, and 2.0 MAC levels of anesthesia (0.90, 1.35, and 1.80% end-tidal halothane) was randomized for every animal. In the awake ponies, cerebral blood flow in the cortical (106 +/- 15 ml/min/100 g) and deep gray (103 +/- 12 ml/min/100 g) matter was approximately 5-fold of that in the white matter (22 +/- 3 ml/min/100 g). In the brain stem, there was a decreasing gradient of blood flow from the cranial (thalamohypothalamus: 65 +/- 8 ml/min/100 g) to caudal regions (medulla: 34 +/- 5 ml/min/100 g). Vasodilatation occurred in all regions of the brain with halothane-O2 anesthesia; the decrease in vascular resistance reached its nadir at 1.5 MAC. In the medulla and pons, blood flow increased above control values, with each of the 3 concentrations of halothane, but in the midbrain and thalamohypothalamus, it remained similar to the control value. In the cerebral white matter and cerebellum, blood flow increased with 1.0 and 1.5 MAC of halothane anesthesia, whereas mean aortic pressure decreased to 91% and 74% of the control value. Blood flow in the cerebral cortex was not different from the control value, even at 2.0 MAC of halothane, despite a 49% reduction in perfusion pressure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of furosemide administration on systemic circulation of ponies during severe exercise

Systemic distribution of blood flow was studied in 11 healthy adult grade ponies, using radionuclide-labeled microspheres (15 micron diameter) that were injected into the left ventricle. Measurements were made at rest, during severe exercise (SE) without furosemide, as well as during SE at 10 minutes and 120 minutes after furosemide administration (1.0 mg/kg, IV). During SE, heart rate, cardiac output, mean aortic pressure, and whole body O2 consumption were 220 +/- 4 beats/min, 720 +/- 44 ml/min/kg, 169 +/- 4 mm of Hg, and 126 +/- 9 ml of O2/min/kg, respectively. With SE performed after furosemide administration, mean aortic pressure decreased from prefurosemide SE value (P less than 0.05), but heart rate, cardiac output, and whole body O2 consumption remained similar to values during SE without furosemide. During SE, blood flow to cerebellar gray matter, pons, and medulla oblongata increased despite marked hypocapnia, but in other regions of the brain, blood flow was unchanged. As arterial O2 content increased by 58% with SE, O2 delivery to all brain regions increased. With SE, adrenal gland blood flow increased, but intense vasoconstriction in the kidneys, spleen, pancreas, small intestine, and colon caused blood flow to plummet. During SE, blood flow in the diaphragm, gluteus medius, biceps femoris (muscles of propulsion), and triceps brachii muscles increased to a similar level, indicating that metabolic requirements of the diaphragm during exercise may not be less than those of other vigorously contracting muscles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Masseter myodegeneration as a cause of trismus or dysphagia in adult horses

The medical records of eight horses with histological evidence of myodegeneration of the masseter muscles were examined. While they were alive their most common clinical signs had included difficulty in eating or opening their mouths, weight loss, difficulty in moving, and noticeable atrophy of the masseter muscles. The serum activities of muscle enzymes were abnormally high in all of the horses. Whole blood and/or liver selenium and vitamin E concentrations were less than the reference ranges in some of the horses. The lesions varied with the stage of the disease and consisted of swelling and discoloration, or muscle atrophy and fibrosis. Histologically, the muscle changes ranged from acute to subacute degeneration, with regenerative changes accompanying ongoing degeneration, to chronic degeneration with fibrotic replacement of muscle tissue. There were changes in the masseter muscle of all the horses, but some had widespread lesions in skeletal muscle, and a few also had myocardial lesions.     

Distribution of blood flow during moderate and strenuous exercise in ponies (Equus caballus)

Blood flow to the brain, heart, kidneys, diaphragm, and skeletal muscles was studied at rest and during graded treadmill exercise, using radionuclide-labeled microspheres (15 microns diameter), in 11 healthy adult ponies. Hemodynamic changes brought about by exercise included marked increases in cardiac output, mean aortic pressure, left ventricular end-diastolic pressure, and right ventricular systolic and end-diastolic pressures. Blood flow to the brain stem and cerebral hemispheres was unchanged during both moderate exercise (heart rate = 154 +/- 3 beats/min) and severe exercise (heart rate = 225 +/- 7 beats/min). Despite marked hypocapnia during severe exercise, cerebellar blood flow increased by 32% above control value (94 +/- 7 ml/min/100 g). Myocardial blood flow increased transmurally with both levels of exercise. The endo:epi (inner:outer) perfusion ratio for the left ventricle and the interventricular septum decreased during exercise. It was, however, not different from unity. During severe exercise, renal blood flow decreased to 19% of its control value. Blood flow to the diaphragm exceeded that to the skeletal muscles during both intensities of exercise. Blood flow to the exercising muscles of the brachium and thigh increased by 31- to 38-fold during moderate exercise and by 70- to 76-fold during severe exercise. It is concluded that the cardiovascular response to strenuous exercise in the pony included an increase in blood flow to the cerebellum, myocardium, diaphragm, and exercising skeletal muscles, while blood flow was diverted away from the kidneys. It would appear that the pony's cardiovascular response to severe exercise is similar to that of persons.     

Accidental monensin sodium intoxication of feedlot cattle

Of 1,994 yearling and 2-year-old cattle in a winter feeding program, 117 died within 42 days of being fed toxic amounts of monensin sodium in a liquid protein supplement. Death losses commenced on the third day after ingestion of a toxic amount in the feed. Clinical signs in cattle that died in less than 9 days included anorexia, pica, diarrhea, depression, mild hindlimb ataxia, and dyspnea. Gross necropsy findings in cattle dying in the acute phase of the illness included hydrothorax, ascites, and pulmonary edema, as well as petechial hemorrhages, edema, and yellow streaking in skeletal and cardiac muscle. Cattle dying after 9 days had gray streaks in heart and skeletal muscle, generalized ventral edema, enlarged, firm, bluish discolored liver, and enlarged heart. Microscopic changes in cattle dying in the acute phase (less than 9 days) consisted of pulmonary edema, congestion, and hemorrhage. Cardiac and skeletal muscle had localized areas of edema, hemorrhage, and coagulative necrosis. In cattle dying after 9 days of illness, the changes included lymphocytic infiltration, sarcolemmal nuclear proliferation, and fibrosis in skeletal and cardiac muscle. Lungs contained increased alveolar macrophages and a few neutrophils. Centrilobular necrosis and mild fibrosis were found in the liver. Changes varied somewhat according to the area of heart or skeletal muscle that was affected. Active muscles, eg, those in the heart ventricles and diaphragm, were altered most severely. Intoxication appeared to be a result of sedimentation of monensin in the molasses carrier to give remarkable concentrations of the substance at the bottom of the holding tank.     

Attempts to restore abduction of the paralyzed equine arytenoid cartilage. I. Nerve-muscle pedicle transplants.

The purpose of this project was to adapt a surgical technique from humans and dogs to horses in which a portion of an accessory muscle of respiration and its nerve supply is transplanted to a denervated dorsal cricoarytenoid muscle. Anatomical dissections in seven horses revealed two possible donor nerve-pedicle grafts: the omohyoid and the sternothyrohyoid, both innervated by a branch of the first and second cervical nerves. Histochemical evaluations in two ponies of the dorsal cricoarytenoid, omohyoid and sternothyrohyoid muscles revealed similar proportions of fiber types 1 and 2 in all three muscles. Electromyographic studies in these two ponies revealed that the omohyoid and sternothyrohyoid muscles contract synchronously with respirations during forced inspiration under general anesthesia. Based on surgical ease of access, a 1 cm2 portion of the omohyoid muscle at the point of penetration of the second cervical nerve was used as a nerve-muscle pedicle graft in an attempt to reinnervate the left dorsal cricoarytenoid muscle in four ponies. These four ponies (as well as three others which served as controls) had previously undergone left recurrent laryngeal nerve transection. All seven ponies endoscopically showed signs of complete left laryngeal hemiplegia immediately postoperatively. Animals were monitored endoscopically for 30 weeks after surgery. The three control ponies showed no abduction of the arytenoid cartilage. In addition, in these three ponies, histological and histochemical expected changes of muscle fiber atrophy and fibrosis were present in the dorsal cricoarytenoid muscle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of halothane, isoflurane, and pentobarbital anesthesia on myocardial irritability in chickens

The relative myocardial irritant properties of halothane, isoflurane, and pentobarbital were evaluated in chickens. Sixteen adult male broiler chickens were randomly assigned to 1 of 3 groups: group-1 chickens were anesthetized with pentobarbital (30 mg/kg, IV), group-2 chickens were anesthetized with halothane (end tidal halothane 1.2%), and group-3 chickens were anesthetized with isoflurane (end tidal isoflurane 2.1%). Birds in any 2 of the 3 treatment groups were tested on any 1 day. Local anesthesia was induced, and blood pressure, heart rate, ECG, and blood gas variables were measured before general anesthesia was induced. Positive-pressure ventilation with an inspired O2 fraction greater than 0.95 was adjusted to result in an end tidal CO2 concentration that reflected a Paco2 similar to that obtained prior to anesthesia and ventilation. All measurements were repeated. The threshold for ventricular fibrillation in response to electrical stimulation of the heart was then determined for all birds. Effects of anesthesia on hemodynamic and blood gas variables were similar in all 3 groups. Compared with halothane or pentobarbital, isoflurane anesthesia resulted in a significantly (P less than 0.05) lower threshold for electrical fibrillation of the heart.     

Regional blood flow changes in response to near maximal exercise in ponies: a review

In recent years, increasing attention has been focused on the physiological responses of the horse to maximal exercise. Cardiovascular response in near maximally exercised galloping ponies (heart rate 225 +/- 7 beats/min; whole body oxygen consumption 122 +/- 12 ml/min/kg) comprised a marked increase in blood flow to the cerebellum, myocardium, diaphragm and the working muscles, while renal blood flow decreased precipitously. Cerebral and brainstem perfusion did not vary from resting values. Transmural homogeneity of myocardial blood flow persisted during near maximal exercise. It was reported that tachycardia of exercise contributed about one-third of the total increment in left ventricular coronary blood flow. Considerable unutilised coronary vasodilator capacity was also demonstrated in near maximally exercised ponies and it was suggested that maximally exercising ponies were not limited from further exertion because of the coronary circulation.     

Isoflurane Anesthesia for Equine Colic Surgery Comparison with Halothane Anesthesia

Isoflurane was compared with halothane as an anesthetic agent for emergency colic surgery in a series of 38 juvenile and adult horses. After presurgical stabilization with fluids and supportive medications, anesthesia was induced by intravenous xylazine and/or diazepam followed by ketamine. Anesthesia was maintained with isoflurane or halothane in oxygen with controlled ventilation. Heart rates (HR), arterial blood gases, mean arterial pressures (MAP), rate pressure products (RPP), requirements for cardiovascular support medications, and recovery times to standing were compared using nonparametric methods. Cardiopulmonary responses to isoflurane and halothane anesthesia were generally comparable although some temporal differences were observed. Higher HR (p less than 0.02) and lower PaCO2 levels (p less than 0.01) were identified during the course of isoflurane anesthesia. Recovery times to standing were significantly shorter (0.02 less than p less than 0.05) after isoflurane than halothane anesthesia.     

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.