Further studies on bovine muscle composition

The average occurrences of fibre types, I,IIA and IIB in the longissimus dorsi (LD) of female cattle were 18%, 59% and 23%, respectively. The IIB occurrence lay between that for bulls and steers, reported in Young & Bass (1984). Since IIB fibres were absent from the splenius (Sp) of females, its composition was more akin to that of bulls than steers. However, the relative area of I and IIA fibres in female Sp was more like that of steers than bulls since IIA fibres were not disproportionately large in females. Evidence suggests that the occurrence of type I (or II) fibres in the LD is rather static and that changes in the occurrence of IIA fibres, reciprocal to IIB, are more common, irrespective of sexual status-bull, steer or female. The route by which IIA and IIB fibres interconvert is discussed. In animals where both the LD and Sp were sampled, the fibre composition of one muscle was a poor predictor of the other's composition. The correlation between the occurrence of I fibres in Sp and succinate dehydrogenese activity in whole muscle was poor, and reasons are advanced to explain this unexpected result. When dark-cutting muscles were excluded from analysis, the average ultimate pH of LD muscles was lower than that of Sp. This result was consistent with the higher type II fibre content of the LD. Ultimate pH of Sp muscles was correlated with occurrence of I fibres, but in the LD a similar relationship could not be established. A link between occurrence of IIB fibres and proneness to the dark-cutting condition is suggested.     

Effect of castration on bovine muscle composition

Samples of bovine muscles were cross-sectioned and stained for myofibrillar ATPase. Three fibre types were distinguished, I, IIA and IIB. In the longissimus dorsi (LD) muscles of steers the average occurrence of IIB fibres was 32%, but in bulls was only 8%. The difference was highly significant. In contrast, the average occurrence of I fibres in steers and bulls was not significantly different. IIB fibres were generally rare in splenius (Sp) muscle, and occurred in some steers but in no bulls. That IIB fibres were more common in steer muscle was confirmed by studies with pairs of identical twins. The increased occurrence of IIB fibres in steers was unrelated to carcass weight changes often associated with castration. Fibre type occurrence data in steer or bull muscles were highly variable. Also, muscles of twins remained macroscopically similar in spite of significant maleness differences between two animals of a pair. Together, these results indicate that castration exerted a relatively minor, but nonetheless significant, effect on the muscles studied. Other factors, such as breed, apparently exert greater effects: LD muscles of Sahiwal × Friesian bulls (a tropical-temperate cross) were very steer-like in composition. Areas of fibres increased with carcass weight. For LD, areas increased with similar slopes in steers and bulls, but for Sp, areas in bulls increased with steeper slopes. This difference related to the increased development of muscles about the neck in bulls. Further, in heavier bulls, areas of IIA fibres were significantly larger than areas of I fibres. Evidence is presented which suggests that the paucity of IIB fibres in bulls and the disproportionate area increases of IIA fibres in bull Sp, relate to the serum concentrations of androgens, which differ markedly in steers and bulls. Possible modes of action of androgens are discussed.     

Histochemical properties of fibre types in muscles of wild and domestic pigs and the effect of growth rate on muscle fibre properties

This study reports the results of a comparison of the histochemical properties of various types of porcine muscles in wild and domestic pigs. In domestic pigs, the influence of growth rates on these properties were studied in five muscles: longissimus dorsi (LD), semimembranosus (SM), gluteus superficialis (GS), infra spinam (IS) and masseter (MAS). The growth rate was expressed as: (i) live weight (LW) at 165±2 days and (ii) daily LW gain from day 88 to day 165 (DG) on the experimental diet. LD, SM, GS and IS of wild pigs were found to contain a higher area percentage of oxidative type IIA fibres (type IIA%(area)) and a lower percentage area of glycolytic type IIB fibres (type IIB%(area)) than the same muscles of domestic pigs. The capillary density in the light muscles (LD, SM, GS) of wild pigs was twice that of domestic pigs, indicating higher oxidative capacity. In domestic pigs the cross sectional area of type IIB fibres (CSA(IIB)) was markedly larger than the cross sectional area of type I (CSA(I)) and IIA (CSA(IIA)) fibres. The average fibre cross sectional area (CSA(fibre)) was about the same in the muscles of wild and domestic pigs except in LD and SM, where the average fibre cross sectional area was approximately 25% smaller in wild pigs than in domestic pigs. This difference was caused by the large cross sectional area of type IIB fibres in the light muscles of domestic pigs. In the light muscles of domestic pigs, the cross sectional area of type IIA fibres increased most with increasing growth rate. Growth rate influences muscle fibre properties only in light muscles, not in dark muscles.     

Mechanical properties of type I and type IIB single porcine muscle fibres

Single muscle fibres were isolated from longissimus dorsi (LD) and vastus intermedius muscles at 1 or 8 days post-mortem. Fibres were classified as type I or IIB and their mechanical properties determined. In LD day 1, individual type IIB fibres fractured at higher (P<0.001) loads and lower (P<0.001) stress values than type I fibres. The strength of type I fibres did not differ between muscles. Storage for 8 days decreased (P<0.001) breaking stress of type I fibres, whereas the breaking stress of type IIB fibres did not change. In conclusion, type IIB fibres were weaker per cross-sectional area than type I fibres in LD. The mechanical properties of type I fibres did not differ between muscles and the change in strength with post-mortem storage were more marked in type I than in type IIB fibres.     

Intramuscular fat and muscle fibre lipid contents in halothane-gene-free pigs fed high or low protein diets and its relation to meat quality

Immediately after exsanguination, samples were taken from M. longissimus dorsi (LD) and M. biceps fermorsi (BF) of halothane-gene-free Swedish Yorkshire pigs (entire males and gilts) fed a high-protein (18·5% crude protein, 0·96% lysine; n = 20) or a low-protein diet (13·1% crude protein, 0·64% lysine; n = 20). The lipid content, measured as triglyceride (TG), was analysed after the samples had been freeze-dried and dissected free from blood, fat and connective tissue. Fibre type composition (type I, IIA, IIB, IIC) was analysed by histochemical staining on all samples. In 14 samples of LD, representing the entire variation of the intramuscular fat content (IMF) among the 40 animals, fibre areas, lipid content and oxidative capacity within the fibre types were evaluated. IMF, meat colour and drip loss were measured in both muscles. Shear force was measured on cooked meat samples from LD. IMF was higher in both LD (2·5%) and BF (2·0%) from pigs on the low-protein diet compared with LD (1·5%) and BF (1·3%) from pigs on the high-protein diet. TG content did not differ between diets in BF but was higher in LD from pigs on low- vis-à-vis high protein diet. A significant correlation was seen in LD between IMF and TG content (r = 0·57; P < 0·001). Fibre type composition did not differ between pigs on the two diets. BF had a higher proportion of type I and IIA fibres and a lower proportion of IIB fibres, compared with LD. TG content in muscle was not correlated with fibre type composition or staining intensity for lipids and oxidative capacity. High staining intensity for lipid in LD was seen in all type I fibres and in some type IIA fibres. Meat quality parameters did not differ between groups except shear force, which was higher in pigs fed the high- vis-à-vis low-protein diet (4·7 and 4·0 kg/cm(2), respectively). Shear force was correlated significantly with TG content (r = -0·42; P < 0·01) and IMF (r = -0·43; P < 0·01) in LD. The results of this study show that lipids are stored mainly in type I fibres and in some type IIA fibres. Intracellular triglycerides account for only a small fraction of IMF. The results indicate that IMF and TG content in muscle fibres may be related to shear force.     

Effects of carcass weight and muscle on texture, structure and myofibre characteristics of wild boar meat

Texture, histology and muscle fibre characteristic of selected muscles: m. quadriceps femoris (QF), m. biceps femoris (BF), and m. semimembranosus (SM) of wild boars of different carcass weight (20±2 and 60±3kgSD) were compared. Muscle texture (hardness, cohesiveness, springiness, chewiness) was determined with the double penetration test performed with the Instron 1140 apparatus. Structural elements (muscle fibre cross-section area, perimysium and endomysium thickness) and percentage of myofibres of each type: I (slow oxidative), IIA (fast oxidative-glycolytic) and IIB (fast glycolytic) per muscle fibre bundle, were measured in muscle samples using a computer image analysis program. The young wild boar muscles showed significantly lower values for the textural parameters (p<0.05). The muscle fibre cross-sectional areas of the juvenile wild boar muscles were significantly lower and the perimysium and endomysium thinner (p<0.05) than those in the old wild boar meat, while the percentage of type IIB fibres was higher. Of all the wild boar muscles tested, the highest hardness and chewiness values were found in BF which, at the same time, showed the highest fibre cross-sectional area and the thickest perimysium and endomysium. The highest percentage of I and IIA fibre types was typical of BF and SM either in young or in old wild boars with the lowest percentage of type I and the highest percentage of type IIB fibres being found in the QF. The results suggest that a higher hardness of wild boar muscles can be connected with a thicker perimysium and endomysium, fibres of higher cross-sectional area and probably a higher content of red fibres (type I).     

Specificity of different anti-myosin heavy chain antibodies in bovine muscle

Muscle fibre types play an important role in bovine meat tenderness, and conditions the speed of ageing. Two generations of myotubes appear during foetal life. Their differentiation results in several types of fibres differing in their contractile and metabolic properties, namely type I fibres and type II fibres (IIA and IIB). Fibre types were identified using antibodies by immunohistochemistry and western-blotting techniques. The aim was to test different antibodies on foetal and adult muscles by these two techniques. Ten monoclonal antibodies reported to be specific to different myosin heavy chain (MHC) isoforms in other species were tested. Only three antibodies were selected: BF.35, specific for I and IIa MHCs, F1.652 specific for foetal MHC and SC.71 an anti II MHCs (IIa and IIb) antibody. The use of these antibodies will enable a more precise characterisation of muscle fibres and will have applications in the study of bovine muscle ontogenesis.     

Characterization of Longissimus thoracis,Semitendinosus and Masseter muscles and relationships with technological quality in pigs. 1. Microscopic analysis of muscles

Three porcine muscles (Longissimus thoracis, Semitendinosus, Masseter), known to have large differences in biochemical and histological traits, were fully characterized and the link between muscle structure and quality evaluated. The oxidative Masseter had more pigment, higher content of metmyoglobin, haem iron, protein and collagen, and was redder with higher fibre numbers, fibre circularity, pH and water holding capacity than the glycolytic Longissimus. Fibre type distribution showed predominance of type IIB in Longissimus and Semitendinosus white, type I in Semitendinosus red and IIA in Masseter. Type I fibres were larger than type IIB and IIA in Semitendinosus and Masseter, respectively, but not in the Longissimus, indicating that fibre size is muscle dependent. Muscle redness was positively correlated with type I fibre traits, haem iron and metmyoglobin, and negatively associated with type II fibre characteristics, non-haem iron and oxymyoglobin. Expressible juice had positive correlation with fibre size and negative with fibre number and connective tissue.     

Effects of massaging on hardness, rheological properties, and structure of four wild boar muscles of different fibre type content and age

Histochemistry (percentage number of three type fibres and their cross-sectional area) and changes in hardness, rheological properties (elastic and viscous moduli), and structural elements (mean fibre cross-sectional area and thickness of endomysium) of four wild boar muscles of different ages: biceps femoris (BF), semimembranosus (SM), quadriceps femoris (QF), and longissimus (L) subjected to effective massaging for 1, 2, 3, and 4 h were evaluated.

BF, with the high percentage of type I fibres, higher mean fibre cross-sectional area, thicker endomysium as compared with QF, SM and L, was harder, more elastic, and more viscous than the other three muscles. Muscles of older boars were found to contain higher percentages of type I fibres, lower percentages of type IIB fibres, bigger muscle fibre cross-sectional areas, thicker endomysium and higher values of hardness than the same muscles of young boars, whereas the percentage of type IIA fibres was about the same in the muscles of both groups. No effect of age on rheological properties was found. Muscle massaging resulted in an increase in the mean fibre cross-sectional area, changes in thickness of the endomysium, reduction in hardness and viscous moduli as well as in the elastic moduli of the muscles studied.

The lower the initial values of textural and structural parameters and percentage of type I fibres of a muscle were, the higher was the muscles susceptibility to massage. BF compared to SM, QF and L, of all the older boar muscles tested compared to those obtained from young boars were less susceptible to mechanical tenderization.     

Muscle glycogen depletion pattern in halothane-gene-free pigs at slaughter and its relation to meat quality

Muscle fibre type composition and glycogen depletion pattern at slaughter as related to meat quality, were studied in M. longissimus dorsi of halothane-gene-free Swedish Yorkshire pigs fed a high (n=19; 10 entire males and 9 gilts) or a low (n=18; 10 entire males and 8 gilts) protein diet. The muscle consisted of, on average, 8% type I, 9% type IIA and 83% type IIB fibres. Muscle fibre areas were significantly smaller in entire male pigs than in gilts irrespective of fibre type. There were no marked differences in muscle characteristics between pigs fed the low and high protein diets. Low glycogen concentrations were found in most type I and type IIA muscle fibres, while a greater variation in glycogen content was evident in type IIB fibres. The pigs were divided into two groups according to the proportion of glycogen depleted IIB fibres (more or less than 30% depleted IIB fibres). In the group where 30% or more of the type IIB fibres were glycogen depleted, a tendency toward DFD meat (dry, firm, dark) was seen, as the meat had higher ultimate pH (5·62 vs 5·52; p=0·02), lower drip loss (2·7% vs 4·4%; p=0·007) and lower reflectance value (darker meat; 16·5 vs 20·6 EEL units; p=0·0005), compared with the group with less than 30% depleted IIB fibres. No difference in total glycogen content was found between these two groups. This indicates that the distribution of glycogen in different fibre types seems to be of importance for the ultimate meat quality.     

Prediction of water-holding capacity and composition of porcine meat by comparative spectroscopy

Forty-one autumn-born Friesian bull calves were allocated to two production systems (Extensive='E' and Intensive='I'). In the E-system, animals were loose-housed and fed a roughage-based diet from October to May, followed by a grazing period from May to October. Ten animals were slaughtered directly from pasture (360 kg BW) and 11 after a 10-week finishing feeding in tie-stalls (460 kg). E-bulls were compared with intensively fed tie-stall housed young bulls (I) slaughtered at comparable weights (360 kg, n=11 and 460 kg, n=9). Semitendinosus (ST), longissimus dorsi (LD), and supraspinatus (SU) muscles were analysed histochemically, and the meat analysed for colour and pigmentation. In LD and SU, Type I % was higher in E- compared with I-bulls (P<0.05-0.006). In ST and LD, Type IIA % was higher in E- compared with I-bulls (P<0.01-0.009). As a result, Type IIB % was lower in all three muscles in E- compared with I-bulls (P<0.05-0.001). In E- compared with I-bulls, Type IIA and IIB fibre areas were larger in ST (P<0.05-0.03) and capillarization was higher in both ST and LD (P<0.001). In all three muscles, the activity of citrate synthase was higher (P<0.07-0.001) and that of lactate dehydrogenase lower (P<0.003-0.001) in E- compared with I-bulls. E-bulls had lower glycogen content than I-bulls in ST and LD at 360 kg, but higher at 460 kg following finishing feeding (P<0.008-0.001). Meat colour (lightness) was darker (P<0.001) and pigmentation was higher (P<0.001) in ST and LD of E- compared with I-bulls, with no effects in SU. In conclusion, histochemically different muscles respond differently to changes in the production system, and differences between the extensive and the intensive production system were narrowed after the finishing feeding.     

Histological and shear properties of bovine muscle and their alteration during postmortem ageing

A total of 108 longissimus dorsi (LD) and 37 semitendinosus (ST) bovine muscles were utilised to evaluate the cellular changes and interrelationships among histological properties during postmortem ageing. The most important cellular change during postmortem ageing in the LD was an increase in the degree of muscle fibre fragmentation (i.e. reduction in the length of muscle fibre fragments) and in the ST a combination of an increase in degree of muscle fibre fragmentation and a lengthening of the sarcomeres. Degree of muscle fibre fragmentation was the most highly and consistently related histological trait to shear force values and interrelationships of LD histological traits indicated that fibres with larger fibre diameters had shorter sarcomeres and fragmented to a lesser degree. In addition, higher incidences of wavy LD fibres were generally associated with shorter sarcomeres post rigor. In general, histological traits within the ST were interrelated only after 13 days of ageing and histological traits among muscles were generally not significantly interrelated.     

Relationship among collagen amount, distribution and architecture in the M. longissimus thoracis and M. pectoralis profundus from pigs

The relative distribution of types I and III collagens and collagen fibre architecture in the perimysium and endomysium were compared to the longissimus thoracis (LT) and pectoralis profundus (PP) muscles in pigs. The LT muscle was composed of type I myofibres 16.8%, IIA 12.9% and IIB 70.2%, and the PP muscle was 25.4, 23.1 and 51.5%, respectively. The total collagen amount differed significantly between the LT (2.66 mg/g) and PP (4.13 mg/g) muscle (P<0.001). On image analysis of the immunohistochemical preparations for types I and III collagens, the percentage area of the perimysium to the total collagen area showed significant differences between the muscles, where perimysial type I collagen occupied 25.4% of the total area in the LT muscle and 45.7% in the PP and perimysial type III 37.6 and 54.5%, respectively (P<0.001). In scanning electron microscopic photographs of the macerated preparation, very thick collagen layers composed of several fibre bands were observed in the perimysia of the PP muscle and appeared differently from the thinner perimysia with a few bands in the LT. Similar architecture of endomysial collagen fibres were observed around every myofibre type in the PP muscle and also in the LT. The fine surface cover of reticular collagen fibres around an adipocyte was shown as a global cast. These results suggested that the total collagen amount of the PP muscle was related mainly to the well developed perimysia composed of several collagen bands, indicating tougher meat compared with the LT muscle.     

Muscle fibre characteristics and metabolic response at slaughter in pigs of different halothane genotypes and their relation to meat quality

Muscle samples for histochemical and biochemical analyses were taken immediately at slaughter from M. longissimus dorsi of pigs with different halothane genotypes (NN and nn). Fibre type composition was similar between groups but the nn-genotype had larger mean fibre areas and lower capillary density than the NN-genotype. At exsanguination the nn-genotype had lower muscle pH (pH(e)), higher lactate and ammonia and lower glycogen and phosphagen (ATP and CP) concentrations and twice as many glycogen-depleted type IIA and IIB fibres as compared with the NN-genotype. Muscle pH(e) was correlated positively to capillary density, glycogen and phosphagen concentrations and negatively to mean fibre area, ammonia and lactate concentrations. Ammonia concentrations were correlated negatively to ATP concentrations and positively to the percentage of glycogen-depleted IIB fibres. The highest reflectance and drip loss values were seen in the nn-genotype. The reflectance values were correlated positively to the percentage of glycogen-depleted type IIB fibres in muscle and the values for drip loss were correlated negatively to pH(e). These data show that fibre size and capillary density in muscle seem to be important factors that influence the metabolic response at slaughter and thus meat quality.     

Relationships of myosin heavy chain fibre types to meat quality traits in traditional and modern pigs

Porcine skeletal muscle fibres were molecularly classified, using in situ hybridisation and immunocytochemistry, into four types, according to the isoform of myosin heavy chain (MyHC) that was present in each fibre (MyHC slow/I, MyHC 2a, MyHC 2x and MyHC 2b). The relationship between MyHC fibre types and meat quality traits between two phenotypically divergent muscles [longissimus dorsi (LD) and psoas], and between the same muscles of different breeds (traditional Berkshire and Tamworth, and modern Duroc-based and Large White-based) were examined. We found that the greater abundance of fast oxidative-glycolytic MyHC 2a and 2x fibres in the psoas was associated with superior meat quality traits, and that the greater presence of fast glycolytic MyHC 2b fibres in the LD could account for less favourable quality traits, both in terms of pH, drip loss, grain, colour, yield force and work done. Although significant correlations were found between specific fibre types and quality traits, within either the psoas or LD muscle of some breeds, no consistent correlation was found across both muscles and all breeds. This finding was in line with the view that a given fibre type could have considerable differences in phenotype between breeds, and between muscles. The observed inverse compositional and functional-meat quality relationship between MyHC 2b and 2x fibres, and MyHC 2b and 2a fibres could form a basis of fibre type manipulation to improve meat quality.     

The biochemical basis of fibre types in bovine muscle

Recent studies using isolated muscle fibres have established a link between the histochemical fibre types, I, IIA and IIB, which can be defined by myofibrillar ATPase activity, and three forms of myosin heavy chain. This work is reviewed, as is work on metabolic variability within these fibre types. Results are them presented which show that the activity of myofibrillar ATPase in sections, although principally determined by the myosin heavy chain, is modified by other myofibrillar components, as yet unidentified. Evidence is also presented for hybrids of myosin heavy chain in muscle fibres. Finally, metabolic variability within the fibre types is examined for bovine muscle. It is concluded that, in spite of wide metabolic variability within types, a classification based on myofibrillar ATPase activity is still useful.     

The relationship between muscle fiber characteristics and meat quality traits of highly marbled Hanwoo (Korean native cattle) steers

To investigate the relationships between muscle fiber characteristics and meat quality traits of Korean native cattle, Hanwoo, Longissimus dorsi (LD), Psoas major (PM) and Semimembranosus (SM) muscles obtained from 18 Hanwoo steers and the muscle fiber characteristics were measured by histochemical analysis. Fiber number, area percentages and density of type IIA and IIB were lower in SM muscle, but higher in PM muscle than other muscles. LD muscle had higher pH_24h, L^? value and fat content whereas SM muscle had lower L^? value and fat content. The lowest WBSF with longer sarcomere length was observed in PM muscle, while SM muscle showed the highest WBSF with shorter sarcomere length. Consequently, the percentage of type I and IIB were highly correlated with meat quality traits and inversely correlated with fat content, L^? value and WBSF. Fiber number and area percentage of type I had a positive correlation with fat content and L^? value and a negative correlation with WBSF. These results suggest that Hanwoo steers had high marbling, more lightness and tenderness when the percentage of type I was high and the percentage of type IIB was low in muscle.     

Myosin heavy chain fibre types and fibre sizes in nuliparous and primiparous ovariectomized Iberian sows: Interaction with two alternative rearing systems during the fattening period

To investigate the effects of the reproductive background (nuliparous/primiparous) on skeletal muscle phenotype and their interaction with two alternative finishing systems (indoors/outdoors) in Iberian sows, 32 contemporary piglets were assigned to four different groups: indoors-nuliparous, indoors-primiparous, outdoors-nuliparous and outdoors-primiparous. Nuliparous sows were ovariectomized at 4 months of age, whereas primiparous were castrated at 14 months of age, after their first lactation. Indoors sows were fattened (2 months prior to slaughter) intensively, whereas outdoors sows were finished in an extensive land with natural resources. Muscle samples (semimembranosus, gluteobiceps) were analyzed for myosin fibre types and fibre sizes. Sows finished out-of-doors had more type I and IIA fibres and smaller fibres than indoor-fattened pigs. Primiparous reared indoors had a significantly lower IIX:IIB fibre ratio and showed a clear tendency for having larger fibres than nuliparous reared indoors. Reproductive background effect interacted with rearing condition effect inducing relevant muscular adaptations. Thus, the influence of reproductive background on muscle characteristics was not significant in sows reared out-of-doors but highly significant in sows finished intensively. This interaction resulted in muscular traits less favourable for meat quality in primiparous vs. nuliparous reared indoors.     

Influences of the method of housing bulls on their body composition and muscle fibre types

The influence of the type of housing (loose or tying-type) was studied in relation to body composition and muscular characteristics of bulls. 34 young bulls (18 Salers and 16 Limousins) were divided into two groups with equal breed representation and equal mean growth rates, to 10 months of age. One group was housed in tying-type housing (short stalls 1·8 m² per animal) and the other in loose housing (6·5 m² per animal). Samples of semitendinosus (ST) and longissimus thoracis (LT) muscle were taken at slaughter at 16 months. The lactate dehydrogenase (LDH) and isocitrate dehydrogenase (ICDH) activities were measured. The proportion of isoforms LDH-M and LDH-H were determined for each muscle. Total collagen content and solubility were measured for ST alone. Fibres were classified by ATPase myofibrillar and succinate dehydrogenase activities into SO (slow oxidative), FOG (fast oxidative glycolytic) or FG (fast glycolytic), and by immunohistochemistry by reaction with monoclonal antibodies specific to slow and fast myosin heavy chain reactions into I, IIC, IIA, IIAB and IIB fibres. Compared with animals in tying-type housing, animals in loose housing presented the following: fewer carcass adipose deposits (p<0·01); for ST muscle, more collagen (p<0·01) and a reduced glycolytic metabolism, as indicated by lower LDH activity (p<0·10) and a lower proportion of FG fibres (p<0·10). In both ST and LT muscles, loose housing resulted in an increased percentage of IIC fibres (p<0·05) but did not alter the proportions of fast fibres. Modifications in ST alone were increased percentage of IIA fibres (p<0·10) and IIAB fibres (p<0·01) and a lower percentage of IIB fibres (p<0·01). Thus, for a given rate of growth, the type of housing (loose or tying-type) influenced contractile characteristics, especially in muscles involved in movement.     

Presence of an unidentified myosin isoform in certain bovine foetal muscles

Genetic variation in the establishment of bovine muscle fibre types was studied by comparing muscle differentiation at 210 days of foetal life in normal cattle and in ‘culard’ animals, which have muscular hypertrophy. The different fibre types were determined by histochemical and immunohistochemical analyses with monoclonal antibodies specific to different myosin heavy chain isoforms. The isoforms were separated by electrophoresis and quantified by the ELISA method. Four muscles with different contractile and metabolic characteristics were studied: Semitendinosus, Longissimus thoracis, Masseter (slow) and Cutaneus trunci (fast). Muscle fibres recognized by none of the antibodies used were observed in ‘culard’ foetuses in all the muscles studied and also in the Cutaneus trunci of normal animals. Electrophoretic analysis showed no particular myosin isoform in these muscles. It is possible therefore that the fibres contained a mysosin isoform until now unidentified in cattle, with a molecular weight the same as that of known isoforms. This newly observed isoform seems to be specific to muscles rich in IIB fibres such as Cutaneus trunci and to the muscles of adult ‘culard’ cattle.