Muscle fibers of pigs sensitive to halothane and resistant to it

The histological and histochemical structure of m. longissimus thoracis, m. semimembranosus, m. triceps brachii-caput longum and m. rectus femoris was compared in pigs with a positive and negative reaction to halothane treatment. As found, the pigs affected by the malignant hyperthermia syndrome have thicker muscle fibres in the studied muscles. In the course of growth, the muscles of these animals have a larger proportion of red fibres (SO), but it is already at the age of 170 days (weight 100 kg) that light fibres prevail. The relative volume of the FG fibres is larger by 1-5%, as compared with the healthy animals. A higher number of pathologically changed fibres occurs in the pigs sensitive to halothane. The histological picture is individually variable; therefore the histological and histochemical methods cannot be considered as objective in view of MHS diagnosis. The general weakening of the constitution of the pigs is discussed as a possible predisposition factor underlying the development of various health disorders.     

Histochemical study of the extensor digitorum longus and soleus muscles in alcoholic rats

The extensor digitorum longus (EDL) and soleus (SOL) muscle fibres from albino rats submitted to experimental chronic alcoholism were evaluated in accordance with their metabolic and morphometric profiles. Twenty-seven male animals aged 4 months and weighing approximately 400 g were used. The animals were divided into three groups: control, isocaloric and alcoholic and sacrifices were carried out after 5, 10 and 15 months. The muscles were dissected, removed, cross-sectioned in a cryostat and submitted to the NADH (nicotinamide adenine dinucleotide) reaction. The SO (slow-twitch-oxidative), FG (fast-twitch-glycolytic) and FOG (fast-twitch-oxidative-glycolytic) muscle fibre types exhibited a polygonal, triangular or rounded shape and did not present noteworthy modifications in either muscles during the study. The cross-sectional areas of the fibres from the studied muscles did not present significant differences during the observations. Fibre area behaved similarly in the alcoholic animals up to the 10th month, i.e. it was decreased, as also observed in the other groups. At 15 months, however, all fibres were increased, with a predominance of FG fibres in the SOL muscle. Changes in fibre population were observed mainly in the SOL muscle of alcoholic animals: SO fibres were initially increased in number but decreased after the 10th month, and the opposite was observed for the population of FG fibres. FOG fibres increased linearly in number throughout the experiment. The statistical analysis showed nevertheless that the fibre population and cross-sectional area changes were not significant. In the alcoholic animals quantitative variations of muscle fibres were more evident in the SOL muscle, suggesting that the SOL muscle is more sensitive to the toxic action of ethanol. The results concerning the increased fibre diameter in alcoholic animals would be associated with muscle oedema induced directly or indirectly by the ethanol.     

Radioimmunoassay of the anabolic agent zeranol. V. Residues of zeranol in the edible tissues, urine, faeces and bile of steers treated with Ralgro

Two trials were conducted on steers implanted with zeranol (Ralgro) to determine the edible tissue residues and the secretion pattern in faeces, urine and bile of zeranol residues throughout and beyond the recommended withdrawal period (70 days) for this drug. In the first trial there was considerable variation in the zeranol residue concentration in all edible tissues, the highest concentrations found in the liver being significantly above the control values (P less than 0.05). In the other tissues, only fat sampled 14 days after implanting was significantly above the control value (P less than 0.05). The zeranol concentration in bile samples obtained at slaughter [70 days (18), 90 days (5) and 120 days (2)] were all higher than the apparent concentration in the bile of untreated steers. The mean concentration of zeranol in the faeces and urine varied from day to day and between animals sampled on the same day following implantation. The highest mean concentrations were observed during the first 40 days following implanting, declining steadily to approach the control values 70 days after implantation. The second trial using steers prepared with bile duct re-entrant cannulae resulted in a similar pattern of zeranol excretion in bile, faeces and urine. The highest concentrations of zeranol were observed in bile and ranged from 24 to 34 micrograms/l; there was considerable variation between animals and within animals sampled on successive days. Although the concentration declined steadily, zeranol was still readily detectable 120 days after implanting.(ABSTRACT TRUNCATED AT 250 WORDS)     

Red muscle development of gilthead sea bream Sparus aurata (L.): structural and ultrastructural morphometry

The transverse red and white muscle area, the superficial red muscle fibres area and their percentages of mitochondria (%mit), myofibrils (%myof) and sarcoplasm (%sarc) were determined in the Mediterranean teleost gilthead sea bream, Sparus aurata (L.). Fish aged from hatching to 78 days were studied. The proportional growth of the red and white muscles was higher for the red muscle in the first half of the larval stage (1-35 days). Then the opposite relationship was observed. The hypertrophic growth of the superficial muscle fibres was continuous except in the first week after hatching. The percentage of mitochondria and percentage of myofibrils showed a significant change just after the half of the larval stage. Whereas the %mit of the superficial muscle fibres was higher than %myof from the first week after hatching to 35 days (average 66.64%), then the %mit decreased significantly and at 73-78 days both parameters were close to an average value of 50%. The meaning of these morphological changes is discussed in relation to the functional role of the red muscle of larvae and the onset of the gills respiration.     

Influence of zeranol implants and electrical stimulation on the palatability traits of five muscles in Angus and Limousin bulls and steers

A split-plot design was used to study effects of male status (bull vs steer), zeranol implants, breed types (Angus vs Limousin) and electrical stimulation on palatability traits of five major muscles when all animals were fed to a similar fat-thickness endpoint. Warner-Bratzler shear (WBS) determinations and taste-panel evaluations were performed on the longissimus, adductor, semimembranosus, semitendinosus and biceps femoris muscles removed 24 h postmortem. Breed was the most consistent main effect difference, with Angus cattle having lower WBS values than Limousin for the longissimus and semitendinosus muscles. Angus cattle also were favored in many sensory traits. Few significant differences were noted between bulls and steers in taste-panel traits. Differences due to electrical stimulation were most evident in the longissimus muscle, with higher panel-evaluation scores, an enhancement of marbling and lean color and a lower incidence of heat ring. The implant tended to have negative effects on palatability in this trial. An overall ranking of the five muscles based on WBS from most tender to least tender was: adductor, semimembranosus, longissimus, semitendinosus and biceps femoris. Correlations of palatability traits of one muscle to other muscles within an experimental unit were found to be low.     

Evaluation of growth, carcass traits and reproductive organs of young boars in response to zeranol implantation

Two experiments were conducted to evaluate the effect of implants containing zeranol on growth rate, carcass composition, palatability and reproductive organ development of intact male pigs. In Exp. 1, three treatment groups were evaluated: control barrows, intact control boars and implanted boars (implanted at either 28, 56 or 112 d of age with one 12-mg dose of zeranol). In Exp. 2, four treatment groups were evaluated: control barrows, intact control boars, boars implanted at 28 d with 24 mg of zeranol (single implant) and boars implanted at 28 d and re-implanted at 56 and 112 d of age with 24 mg of zeranol (triple implant). Differences for average daily gain and carcass traits were not consistent between treatment groups with the exception of 10th rib fat, where barrows were fatter than boars. There were no differences among treatments due to zeranol for the reproductive organ characteristics, with the exception that bulbourethal gland and teat weights were heavier for boars in Exp. 2. Penis weights and lengths were lower for barrows in both experiments. Juiciness, tenderness, Warner-Bratzler shear force, pork flavor intensity and sensory scores were not consistently affected by male condition or zeranol treatment. In two of the three comparisons, implanted boars had higher off-flavor intensity scores in Exp. 1, but no treatment difference was observed in Exp. 2. Zeranol implantation did not result in significant changes in growth rate, development of reproductive organs or carcass characteristics of young boars.     

The effects of zeranol on growth and fattening in beef calves before weaning

Four-month-old beef calves were implanted with 36 mg zeranol, and their growth compared with untreated calves. Treated steer and heifer calves gained 10 kg more bodyweight to weaning at 7.5 months of age. The trial was conducted at 2 research centres and calves at both centres showed significant responses for the first 45 days (P less than 0.001) after treatment but during the following 30 days only calves at one centre showed a continued response (P less than 0.05). No differences in growth rate occurred between treated and untreated calves over the final 30 days before weaning at either centre. The backfat measurement of untreated animals increased more than that of the implanted animals (P less than 0.05) at one centre but not at the other.     

Characteristics of myofibres in the masseter muscle of mice during postnatal growth period

Functional maturation of muscles is related to the constitutional proportion of muscle protein isoforms during development and growth. Although the mouse masseter muscle (MS) is classified as a fast limb muscle, its functions are different from those of a limb muscle. This study investigated the differentiation of myosin heavy chain (MHC) isoforms during the postnatal development periods in mouse MS and mouse tibialis anterior (TA), which is a fast limb muscle. Many anti-MHC slow-type-positive fibres were observed in neonatal MS and TA; these fibres decreased during development. Adult MS was composed of anti-MHC fast-type-positive fibres. MHC isoforms in MS were composed of MHC-2a and MHC-2d soon after birth. MHC-2b was expressed, but MHC-2a was not seen after 21 days. Expression of MHC-2b agreed with the weaning period, that is 2-3 weeks after birth. This fact suggested that the transformation from suckling to mastication changed the MHC isoforms during this period. In this study, the expressions of MHC-2b agree with the weaning period.     

Radioimmunoassay of the anabolic agent zeranol. IV. The determination of zeranol concentrations in the edible tissues of cattle implanted with zeranol (Ralgro)

Rapid solvent extraction combined with a radioimmunoassay using a monoclonal antibody raised against a derivative of zeranol has been used to measure the residues of the anabolic agent zeranol in the edible tissues (muscle, liver, kidney and fat) of cattle treated with Ralgro. Calibration curves, both with and without, tissue extracts exhibit good parallelism. Regression analysis for the extraction of zeranol from tissues dosed with standard amounts of zeranol have correlation coefficients of 0.979, 0.991, 0.986 and 0.985 for muscle, liver, kidney and fat, respectively. The limits of decision defined as the mean value + 3 SD for the concentrations apparently observed (noise) in tissues from animals not treated with Ralgro were 278, 121, 373 and 110 ng/kg for muscle, fat, liver and kidney, respectively. In the tissues of 4 cows implanted with Ralgro (36 mg), and sampled 70 days after implanting, the highest concentration of zeranol in each tissue was 232 ng/kg (muscle), 391 ng/kg (liver), 287 ng/kg (kidney) and 293 ng/kg (fat), and residues were detected in all samples of fat (4), 3 kidney samples and 1 liver sample.     

Myosin Heavy Chain Transitions in Dog Skeletal Muscle Fibres during Post-natal Development

Myosin heavy chain (MHC) isoform expression was established in the masseter, axial and limb skeletal muscles in 18 young dogs from late prenatal to 6 months of age. Results obtained by immunohistochemical procedure using 11 monoclonal antibodies, SDS-PAGE electrophoresis, Western-blotting and enzyme-histochemical reactions were compared to those found in skeletal muscles of adult dogs. In the skeletal muscles of both fetuses in the last stages of development and neonatal dogs, the developmental isoforms MHC-emb and MHC-neo were prevalent. During the first 10 days after birth, the level of embryonic isoform expression declined, as did that of the neonatal isoform during the second and third weeks. Correspondingly, the expression of MHC-IIa, and later, of MHC-I increased. By 6 weeks of age the presence of MHC-IIx became obvious. This transitional pattern was similar in all muscles except in the rhomboideus, where secondary slow fibres were present before birth. In the other muscles, only one primary, centrally located, slow fibre was present in a fascicle and the secondary slow fibres evolved from developmentally fast fibres between the second and third weeks of age. Our results indicate that timing of muscle maturation depends on its activity right after birth. The fastest developing muscles were the masseter muscle and the diaphragm. They were followed by others, postural and locomotory muscles. A pronounced swap from developmental to adult isoforms was noted between the 4^th and 6^th week of age. At this age puppies are weaned and begin playing intensively and investigating their surroundings. The results of our study indicate that dog skeletal muscles exhibit an immature morphology at birth and develop relatively slowly compared to those of other domestic animals.     

Effects of zeranol implants on post-castration response in calves

SUMMARY Suckling and yearling calves were surgically castrated and one half of each group implanted with 36 mg zeranol at time of castration. Both treated and control cattle of each class were maintained as a group and evaluated for swelling of the scrotum, inflammation and healing, plasma prostaglandin levels and weight gain. Swelling and inflammation of the scrotum were less in treated suckling calves than in controls at both 7 and 14 d after castration, though this difference was not statistically significant. In yearlings at 7 d after castration, treated cattle had more swelling than controls; however at 14 d, treated cattle had less swelling and inflammation with only one treated yearling having an open scrotal wound versus 6 (P <.03) in the control group. Plasma prostaglandin levels as indicated by plasma malondialdehyde increased from d 0 to 14; however no significant treatment differences were observed for either age group. Suckling calves treated with zeranol gained 9.79 kg more (P <.03) than non-treated calves during the 97 d of trial while the yearlings treated with zeranol gained 16.78 kg more (P <.01) than controls during 102 d. It is concluded from the increased growth and reduced scrotal swelling and inflammation in treated cattle that zeranol implantation could possibly have a beneficial effect in improving the healing process after castration.     

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.     

Temperature effect on muscle growth of the axial musculature of the sea bass (Dicentrarchus labrax L.)

In order to determine the temperature effect on the axial muscle growth of sea bass, a stock of larvae was subjected to the following incubation and cultivation temperatures, respectively: 15 degrees C/ambient, 15/17 degrees C, 17 degrees C/ambient and 17/17 degrees C. In all groups the cross-sectional area of white and red muscles and the number and average area of the white and red muscle fibres were quantified. Results showed that the embryonic period, pre-larval phase and the end of metamorphosis were accelerated at higher temperatures. During the endogenous feeding period, muscle growth took place by fibrillar hypertrophy, and was not influenced by the temperature. Thereafter (external feeding) muscular hyperplasia began, and growth of all the muscular parameters was favoured by the effect of high incubation and cultivation temperatures, with the latter having higher influence. High incubation temperature had an slight effect on muscle growth and body length, which was only observed from 15 days. Metamorphosis finished at 3 +/- 0.4 cm in all the larvae, but this length was earlier reached at higher temperatures. At 120 days, the largest growth was obtained in the larvae maintained at a higher temperature.     

Blood and serum components and organ weights in steers, bulls and zeranol-implanted bulls

To investigate certain physiological aspects of the mode of action of zeranol or Ralgro on growth, behavior and carcass quality of young bulls, concentrations of 19 blood components and weights of eight organs were determined. Experimental animals consisted of 36 untreated steers, 36 untreated bulls, 36 bulls implanted with zeranol at 3 mo of age and subsequently at 5, 8 and 10 mo and 36 bulls implanted with zeranol at 6 mo of age and subsequently at 9 and 11 mo. In addition, half of the animals in each group were subjected to moderate pre-slaughter stress (mixing and trucking 160 km); the other half was subjected to minimum pre-slaughter stress (no mixing and 4 km transport). Concentrations of cortisol, urea nitrogen and albumin in serum were higher (P less than .01) and those of glutamic oxaloacetic transaminase (GOT), lactate dehydrogenase (LDH), alkaline phosphatase (AP) and creatinine were lower (P less than .05) in steers than in intact males. Concentrations of GOT, LDH, and creatinine were higher (P less than .05) in implanted than those in control males. Pre-slaughter stress had a significant effect on several traits measured in blood or serum. Thyroid glands were smaller (P less than .01) in steers than in control and implanted males. Testes were smaller (P less than .01) in the zeranol-implanted than in untreated males. Results indicate that zeranol had only a minor effect on the 19 blood components studied, but it did reduce testicle size. Castration had a major impact on several of the blood components. Pre-slaughter management had a significant effect on several blood components.     

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     

Gender differences in the morphometric properties of muscle fibres and the innervation ratio of motor units in rat medial gastrocnemius muscle

With 2 figures and 2 tables SUMMARY: Previous studies of motor unit contractile properties in the rat medial gastrocnemius revealed that these units generate higher forces in males than in females. Therefore, in the present study the number and morphometric parameters of muscle fibres and the innervation ratio of motor units in the medial gastrocnemius muscle were studied in male and female Wistar rats. The study additionally aimed at determining reasons of gender differences in motor unit force parameters, i.e. the number and diameter of muscle fibres, and mean values of the motor unit innervation ratios. Following staining of reticuline fibres by silver impregnation, the number, diameter and cross-section area of muscle fibres were determined on microscopic images of transverse muscle sections. In males, the muscles were approximately 1.5 times larger by mass and contained about 11 800 muscle fibres, whereas in females the muscles contained around 8000 fibres. In addition, the mean diameter and mean cross-section area of muscle fibres were 14 and 29% larger in males, respectively. Based on previously determined numbers of motoneurons innervating the medial gastrocnemius muscle in male and female rats, the mean innervation ratio, i.e. the number of muscle fibres innervated by one motoneuron, was estimated. This ratio was approximately 26% greater in males compared to females, with values of 207 and 153 fibres per motoneuron, respectively. Therefore, the differences in muscle fibre morphometric parameters and in the innervation ratio are responsible for higher forces of motor units in male muscles.     

Morphometry and histochemistry of the semitendinosus muscle of tufted capuchin monkeys (Cebus apella Linnaeus, 1758)

Considering monkeys are animals closely related to the human, and semitendinosus muscle has been used in many postural research experiments, we have decided to study its histochemical characteristics. Samples were removed from the proximal, middle and distal regions of the semitendinosus muscles of five adult male tufted capuchin monkeys and observed for reaction with m-ATPase (with alkaline and acid pre-incubation), nicotinamide adenine dinucleotide tetrazolium reductase, and haematoxylin and eosin. The muscle fibres were classified as fast glycolytic (FG), fast oxidative glycolytic (FOG) and slow oxidative (SO) and quantified in terms of frequency and area. The three regions of the semitendinosus muscle showed no significant differences in frequency or area of the respective fibre types, and therefore the muscle can be considered histoenzymologically homogeneous. FG fibres presented higher frequencies and larger areas. The sum of FOG and SO fibres was 57.5%, suggesting that the semitendinosus muscle of the tufted capuchin monkey is adapted to an action involved in posture maintenance and in long arboreal dislocation. The present data agrees with the notion of differentiated quadrupedalism in some primates, which support a lower percentage of their weight on the fore limbs.     

Relation between myoglobin levels and succinate dehydrogenase activity in muscle fibers

We compared the histochemical activity of succinate dehydrogenase (SDH) and the intensity of reaction to the presence of myoglobin (Mb) in the same muscle fibres m. longissimus thoracis (MLT), m. semimembranosus (MSM), m. rectus femoris (MRF) and caput longum m. tricipitis brachii (MTB). At the same time we also ascertained the myoglobin content of one gram of fresh muscle. We found that the muscle fibre in all the muscles studied in which there is the most intensive reaction in the test for SDH are also the most intensively coloured in the test for Mb. There is also the same relationship in intermediary and white fibres. The reaction in testing for SDH on a cross section is greatest in the subsarcolemmic area. Similar tendencies appear in the distribution of Mb, although they are less marked and only in fibres with intensive reaction. Different muscles have different myoglobin levels. Muscles with a higher proportion of red and intermediary fibres contain more myoglobin than muscles with a high proportion of white fibres. The quantitative values of the levels of Mb (g/fresh muscle) are not, however, proportional to the share of individual types of muscle fibres in the muscles studied.     

Effect of long or short acting anabolic agents, given singly or repeated, on growth rate and carcase weight of steers

A trial was carried out using 490, 12- to 15-month-old steers which were at pasture from April to November and then housed and fed grass silage and concentrates until sold live or slaughtered. Animals were allocated at random to one of the following treatments: (i) Control; (ii) implanted with 45 mg oestradiol -17 beta in silastic rubber in April; (iii) implanted with oestradiol in April and with 300 mg trenbolone acetate in April, August and November; (iv) implanted with 36 mg zeranol in April, August and November and (v) implanted with zeranol and trenbolone acetate in April, August and November. Daily liveweight gains were 0.69, 0.75, 0.78, 0.83 and 0.86 (+/- 0.02) kg, and carcase weights were 300, 306, 311, 316 and 321 (+/- 3.4) kg, for treatments (i) to (v), respectively. All implanted animals had significantly higher daily gains than control animals and an additive response was obtained where trenbolone acetate was used with oestradiol or zeranol. Pooled results for animals treated with oestradiol plus zeranol, with or without trenbolone acetate, show that the overall response for zeranol treated animals was higher than from the animals treated with oestradiol. Daily gains after the first, second and third implant period show a reduced response from the oestradiol implant for the final 63 days of the trial. This may have been caused by loss of some oestradiol implants from animals early in the trial.     

The influence of the PRKAG3 mutation on glycogen,enzyme activities and fibre types in different skeletal muscles of exercise trained pigs

Background

AMP-activated protein kinase (AMPK) plays an important role in the regulation of glucose and lipid metabolism in skeletal muscle. Many pigs of Hampshire origin have a naturally occurring dominant mutation in the AMPK γ3 subunit. Pigs carrying this PRKAG3 (R225Q) mutation have, compared to non-carriers, higher muscle glycogen levels and increased oxidative capacity in m. longissimus dorsi, containing mainly type II glycolytic fibres. These metabolic changes resemble those seen when muscles adapt to an increased physical activity level. The aim was to stimulate AMPK by exercise training and study the influence of the PRKAG3 mutation on metabolic and fibre characteristics not only in m. longissimus dorsi, but also in other muscles with different functions.

Methods

Eight pigs, with the PRKAG3 mutation, and eight pigs without the mutation were exercise trained on a treadmill. One week after the training period muscle samples were obtained after euthanisation from m. biceps femoris, m. longissimus dorsi, m. masseter and m. semitendinosus. Glycogen content was analysed in all these muscles. Enzyme activities were analysed on m. biceps femoris, m. longissimus dorsi, and m. semitendinosus to evaluate the capacity for phosphorylation of glucose and the oxidative and glycolytic capacity. Fibre types were identified with the myosin ATPase method and in m. biceps femoris and m. longissimus dorsi, immunohistochemical methods were also used.

Results

The carriers of the PRKAG3 mutation had compared to the non-carriers higher muscle glycogen content, increased capacity for phosphorylation of glucose, increased oxidative and decreased glycolytic capacity in m. longissimus dorsi and increased phosphorylase activity in m. biceps femoris and m. longissimus dorsi. No differences between genotypes were seen when fibre type composition was evaluated with the myosin ATPase method. Immunohistochemical methods showed that the carriers compared to the non-carriers had a higher percentage of type II fibres stained with the antibody identifying type IIA and IIX fibres in m. longissimus dorsi and a lower percentage of type IIB fibres in both m. biceps femoris and m. longissimus dorsi. In these muscles the relative area of type IIB fibres was lower in carriers than in non-carriers.

Conclusions

In exercise-trained pigs, the PRKAG3 mutation influences muscle characteristics and promotes an oxidative phenotype to a varying degree among muscles with different functions.