Review: On-farm and processing factors affecting bovine carcass and meat quality

This paper reviews the current state of knowledge on beef carcass and meat quality, with particular emphasis on on-farm and processing factors associated with its high and inconsistent variability. The diversity of livestock systems comes from the diversity of breeds (dairy or beef), ages and gender (bulls, steers, heifers, cull cows) used to produce either mainly beef or beef and milk. In addition, there are factors linked to farming practices (including diet, especially grazing) which significantly influence the sensory, nutritional, technological and extrinsic (such as image) quality attributes of meat. These can become factors of positive differentiation when controlled by the application and certification of technical specifications. Finally, preslaughter (such as stress), slaughter (such as the chilling and hanging method of carcasses) and postslaughter (such as ageing, packaging and cooking) conditions have a strong influence on the microbiological, sensory, technological and image quality attributes of beef. In this review, potential synergisms or antagonisms between the different quality attributes are highlighted. For example, finishing cattle on grass, compared to indoor fattening on a high concentrate diet, has the advantage of producing leaner meat with a higher proportion of omega-3 fatty acids while exhibiting superior oxidative stability, but with the consequence of a darker meat colour and lower productivity, as well as higher seasonality and land surface requirements. Moreover, the control of on-farm factors is often guided by productivity (growth rate, feed conversion ratio) and carcass quality attributes (weight, conformation and fatness). Genetic selection has often been oriented in this direction, without taking other quality attributes into account. Finally, the interactions between all these factors (and especially between on-farm and slaughter or processing factors) are not considered in the quality grading schemes in European countries. This means that positive efforts at farm level may be mitigated or even eliminated by poor slaughtering or processing conditions. All these considerations explain why between-animal variability in quality can be high, even when animals come from the same farming system. The ability to predict the sensory and nutritional properties of meat according to production factors has become a major objective of the supply chain.

Fine mapping of quantitative trait loci underlying sensory meat quality traits in three French beef cattle breeds

Improving the traits that underlie meat quality is a major challenge in the beef industry. The objective of this paper was to detect QTL linked to sensory meat quality traits in 3 French beef cattle breeds. We genotyped 1,059, 1,219, and 947 young bulls and their sires belonging to the Charolais, Limousin, and Blonde d'Aquitaine breeds, respectively, using the Illumina BovineSNP50 BeadChip (Illumina Inc., San Diego, CA). After estimating relevant genetic parameters using VCE software, we performed a linkage disequilibrium and linkage analysis on 4 meat traits: intramuscular fat content, muscle lightness, shear force, and tenderness score. Heritability coefficients largely ranged between 0.10 and 0.24; however, they reached a maximum of 0.44 and 0.50 for intramuscular fat content and tenderness score, respectively, in the Charolais breed. The 2 meat texture traits, shear force and tenderness score, were strongly genetically correlated (-0.91 in the Charolais and Limousin breed and -0.86 in the Blonde d'Aquitaine breed), indicating that they are 2 different measures of approximately the same trait. The genetic correlation between tenderness and intramuscular fat content differed across breeds. Using a significance threshold of 5 × 10(-4) for QTL detection, we found more than 200 significant positions across the 29 autosomal chromosomes for the 4 traits in the Charolais and Blonde d'Aquitaine breeds; in contrast, there were only 78 significant positions in the Limousin breed. Few QTL were common across breeds. We detected QTL for intramuscular fat content located near the myostatin gene in the Charolais and Blonde d'Aquitaine breeds. No mutation in this gene has been reported for the Blonde d'Aquitaine breed; therefore, it suggests that an unknown mutation could be segregating in this breed. We confirmed that, in certain breeds, markers in the calpastatin and calpain 1 gene regions affect tenderness. We also found new QTL as several QTL on chromosome 3 that are significantly associated with meat tenderness in the Blonde d'Aquitaine breed. Overall, these results greatly contribute to the goal of building a panel of markers that can be used to select animals of high meat quality.

Win–win strategies for high beef quality, consumer satisfaction, and farm efficiency, low environmental impacts and improved animal welfare

Meat quality includes intrinsic qualities (the characteristics of the product itself) and extrinsic qualities (e.g. animal health and welfare, environmental impacts, price). There is still a high level of variability in beef palatability, which induces consumer dissatisfaction. We also observe a general trend towards an increasing importance of healthiness and safety (intrinsic) and environmental issues and animal welfare (extrinsic). Most grading systems describe carcasses using only animal traits (e.g. weight, conformation, fatness, animal age and sex). In North American and Asian countries, emphasis has been put on maturity and marbling. The European system is mainly based on yield estimation. The Meat Standards Australia grading scheme, which predicts beef palatability for each cut, proved to be effective in predicting beef palatability in many other countries. Some genetic markers are available to improve beef quality. In addition, gene and protein expression profiling of the bovine muscle revealed that the expression level of many genes and the abundance of many proteins may be potential indicators of muscle mass, tenderness, flavour or marbling of meat. The integration of all these parameters is likely to predict better beef palatability. The integration of extrinsic qualities in the prediction model increases the difficulty of achieving a global evaluation of overall meat quality. For instance, with respect to environmental issues, each feeding system has its own advantages and disadvantages. Despite this, win–win strategies have been identified. For example, animals that were less stressed at slaughter also produced more tender meat, and in some studies the most economically efficient farms had the lowest environmental impact. In other cases, there are trade-offs among and between intrinsic and extrinsic qualities. In any case, the combination of the different integrative approaches appears promising to improve the prediction of overall beef quality. A relevant combination of indicators related to sensory and nutritional quality, social and environmental considerations (such as e.g. carbon footprint, animal welfare, grassland biodiversity, rural development) and economic efficiency (income of farmers and of other stakeholders of the supply chain, etc.) will allow the prediction of the overall quality of beef mainly for consumers but also for any stakeholder in the supply chain.

Chemical composition and structural characteristics of Arabian camel (Camelus dromedarius) m. longissimus thoracis

Saudi Arabian camels of four breeds (6 animals per breed) were used to evaluate characteristics and quality of their meat. Chemical composition, fibre cross sectional area, collagen content, muscle metabolism, cooking loss, pH at 24 h post mortem, colour values (except redness) and shear force of Longissimus thoracis (LT) muscle did not differ between the breeds. Elevated pH values and short sarcomeres reduced overall tenderisation, with a difference between myofibril fragmentation index (P<0.001) and sarcomere length (P<0.05) between breeds. A positive correlation was observed between the activities of the mitochondrial enzymes (r>0.49), between the glycolytic activities (PFK and LDH) (r=0.61) and between Myosin Heavy Chain IIa and LDH activity. The intramuscular fat content was positively associated with redness and muscle oxidative metabolism, whereas shear force had a slight positive association with collagen content and muscle glycolytic metabolism and a negative association with muscle oxidative metabolism and muscle fibre area.

The challenge and limitations of combining data: a case study examining the relationship between intramuscular fat content and flavour intensity based on the BIF-BEEF database

The BIF-BEEF (Beef Integrated and Functional Biology) data warehouse for muscle biology to predict beef quality gathers data related to bovines, their carcasses and their beef. These data come mainly from three sources: the INRA database named FiLiCol, the European GEMQUAL program and the French QUALVIGENE program databases plus other minor sources. At the beginning of 2011, the BIF-BEEF data warehouse contained 331 745 measurements for 621 variables. Measurements were obtained on eight muscles and/or from 5197 animals (mainly young bulls) belonging to 20 different breeds (mainly Charolais, Limousin, Blonde d’Aquitaine, the three major French beef breeds) from experiments carried out over a 10-year period. A web interface was developed to extract data and to analyse them using basic statistical tools (correlation, variance analysis, etc) with R software. Clearly, since the various experiments were not designed initially to ultimately link together, it appeared very difficult to integrate some data which differ a lot by units, scales or laboratory methods. Ontology will help to address these issues. However, the usefulness of the BIF-BEEF data warehouse is described by studying the relationship in M. longissimus thoracis between intramuscular fat content (IMF) and flavour assessed by sensory panels. When data from different sources or different sensory panels were used, they were corrected for these fixed factors in the regression model. They were also corrected for known sources of variation (sex, breed and age of the animals). On average, the relationship between IMF and flavour was low (partial correlation coefficient r = 0.11) but significant. This relationship was no more significant for breeds with low IMF levels (such as Blonde d’Aquitaine) or for animals with the highest IMF such as steers or females.

Current and future issues facing red meat quality in a competitive market and how to manage continuous improvement

This paper discusses current and future issues facing lamb and beef meat quality and proposes strategies to manage quality improvements into the future. Based on survey data of Australian consumers and whole supply chain profit drivers, it is argued that the three most important quality areas for future research are lean meat yield, eating quality and human nutritive value. These areas have complex biological interactions, both antagonistic and complimentary, which require careful management so as to produce the best outcome for industry and the consumer. It is argued that the best way forward is to undertake collaborative research that encompasses industry production, meat science and genetics simultaneously. The case study of the Australian lamb industry is used as a suggested model for future progression, whereby a large breeding program forms the central focus of numerous research and delivery activities. Another issue raised is the need for strong and cost-effective industry systems that are able to effectively utilise outcomes from genetics, lean meat yield and eating quality to deliver the research results.

Perception in France of the Australian system for the prediction of beef quality (Meat Standards Australia) with perspectives for the European beef sector

Australia has developed the Meat Standards Australia (MSA) grading scheme to predict beef quality for consumers. This system is comprehensive, accurate and scientifically supported. It is based on the development and the use of a research database with a large amount of data, including the use of a large-scale consumer testing system with cuts cooked in different ways as well as information on the corresponding animals, carcasses and cuts. The system is also based on statistical analyses carried out on this database to identify the critical control points of beef palatability which is indicated for individual muscles and for a specific cooking method and aging time. Experts involved in the French beef industry were questioned about their knowledge and views on the application of the MSA system. They recognised many qualities of the MSA system and it was judged as original, relevant and sufficiently mature in its application, and favouring scientifically based prediction of beef quality rather than replying on tradition and perceptions of quality. It was also thought to be credible, flexible and open ended. However, it was still considered to possess some weak points. Thus, while its development in Australia at the farmer and abattoir level has been impressive in a relatively short time, the final delivery of precise quality grades to consumers is still lacking at retail due to only partial implementation of the system. Its adaptability to France would be difficult due to the complexity of the French beef industry and market. But, the program is uniquely innovative and deserves consideration. It will facilitate awareness and induce much needed changes to underpin the preservation and the development of the beef sector in France and eventually in Europe.

Future research priorities for animal production in a changing world

This paper reports the outcomes from an International Workshop on ‘Animal Production in a Changing World’ held in Clermont-Ferrand (INRA-Theix, France) on 9–10 September 2009 in which 35 participants from 15 different countries participated. The main objective was to discuss the main challenges within the livestock sector: its environmental impact and role in global climate change; balancing the need for increased production of animal products coupled with a lower footprint and addressing societal needs in terms of product quality for the consumer. Five key lectures presented the main drivers of animal agriculture: population growth, environmental impact, mitigation and adaptation options, efficiency of production and quality of animal products. The key lectures highlighted the synergies between research needs and strategies dedicated to improving food quality and safety and those devoted to decreasing the environmental impact of ruminant livestock production. After the lectures two discussion groups were set up to discuss the main research priorities in relation to reducing environmental footprint and improving product quality. The main remarks from the group working on product quality were that the existing knowledge is not fully applied, the priorities with regards to quality differ between developing and developed countries and that, as one component in assessing food quality, an environmental index needs to be established taking into account carbon footprint, water and energy use. The discussion within the group working on environmental issues highlighted the importance of focusing on whole life cycle analysis in the mitigation area, while the adaptation strategy should be based on selection for profitable animals under different production systems. In summary, a fundamental shift in designing our production systems is required to help ensure present needs for animal products are met without compromising future generations.

Gene expression and protein content in relation to intramuscular fat content in Muscovy and Pekin ducks

Independent of their nutritional condition, Pekin ducks always exhibit higher i.m. fat content than Muscovy ducks. To understand this difference between species, the expression level of genes involved in lipid metabolism was analyzed in the pectoralis major muscle of Pekin and Muscovy ducks ad libitum-fed or overfed. The lipoprotein lipase (LPL) gene expression was not different between species and not influenced by overfeeding. The protein content for LPL was higher in Pekin ducks than in Muscovy ducks when birds were ad libitum-fed, whereas in overfed ducks, we found no difference between species. Adipocyte fatty acid-binding protein (A-FABP) gene expression and protein content were higher in Pekin ducks than in Muscovy ducks for each nutritional condition (suggesting a higher intracellular transport within i.m. adipocytes of fatty acids mainly provided by liver for this species). Overfeeding did not affect the expression of genes involved in oxidation [carnitine palmitoyl transferase 1A (CPT1A), cytochrome-c oxidase 4 (COX4), succinyl-coenzyme A:3-ketoacid coenzyme A transferase (SCOT)] but increased the expression of fatty acid synthase (FAS) involved in lipogenesis. For all nutritional conditions, Pekin duck exhibited higher expression levels of CPT1A, COX4, SCOT, and FAS than Muscovy ducks. Results for mRNA SCOT suggested that the muscles of Pekin ducks use ketone bodies as an energy source. In conclusion, i.m. lipogenesis could contribute to the i.m. fat, particularly in Pekin ducks.

Contribution of genomics to the understanding of physiological functions

Genomics has brought with it a true biological revolution and can be applied to all areas of life sciences. The advent of genomics is thus linked to the development of high-throughput techniques which allows the genome of organisms as a whole to be studied. The first high-throughput techniques to be developed were sequencing methods. These advances will allow new approaches to a variety of problems in biology. For instance, the emerging fields of genomic medicine in humans and genomic selection in livestock are promising. After the sequencing of genomes, genomics has shifted to the study of gene expression and function. This is called the "post-genomic area" by some authors or "functional genomics" by others. The most recent "omics" to be developed are associated with the study of the metabolism (e.g. metabolomics). Integrative "omics" approaches (e.g. nutrigenomics) are based on the association of the omics tools at different levels (DNA, RNA, proteins, metabolites) for a specific objective (here nutrition). In terms of perspectives, it is likely that methods for collecting data will outstrip our capacity to adequately analyse these data. So scientists must develop bioinformatic tools and methods to overcome this difficulty. In addition, high-throughput techniques need to be developed in physiology in order to match the increasing amount of genomic information with true biological data. Finally, there is no doubt that all these new approaches will allow important new genes and novel biological mechanisms to be discovered. Physiological models with invalidated or over-expressed genes will be precious tools to check these new biological discoveries.

Adipocyte fatty acid-binding protein and mitochondrial enzyme activities in muscles as relevant indicators of marbling in cattle1

Marbling is an important criterion for beef quality grading in many countries. The purpose of the current study was to utilize the natural genetic variation to identify major metabolic indicators of marbling in cattle differing in genotypes. Rectus abdominis (RA, oxidative), semitendinosus (glycolytic), and longissimus thoracis (LT, oxido-glycolytic) muscles were taken from steers of different genotypes that expressed high [Angus, n = 16; and crossbred (Angus x Japanese Black), n = 10] or low (Limousin, n = 12) levels of marbling in their meat. Muscles from Angus and crossbred steers were characterized, as expected, by a greater triacylglycerol (TAG) content (P < 0.001) and also by greater protein contents of fatty acid-binding protein specific for heart and muscles (H-FABP; P < 0.001 for RA and P < 0.05 for LT muscle) or for adipocytes (A-FABP; P < 0.001 for RA and LT muscles). Moreover, oxidative enzyme activities (beta-hydroxyacyl-CoA dehydrogenase, citrate synthase, isocitrate dehydrogenase, cytochrome-c oxidase) were greater (P < 0.01 to 0.001) in the 3 muscles studied, whereas glycolytic enzyme activities (phosphofructokinase and lactate dehydrogenase) were lower (P < 0.001) in RA muscle in Angus and crossbred steers compared with Limousin steers. Significant correlations were observed between TAG content and H- and A-FABP protein contents, and oxidative (r > or = +0.55, P < 0.001) or glycolytic enzyme activities (r > or = -0.47, P < 0.001), when the 3 genotypes and muscles studied were considered as a whole. In addition, A-FABP protein content and some oxidative enzyme activities were significantly correlated with TAG content independently of the genotype and muscle effects. In conclusion, A-FABP protein content, as well as oxidative enzyme activities, may be used as indicators of the ability of steers from extreme genotypes to deposit intramuscular fat.

Relationships between thyroid status, tissue oxidative metabolism, and muscle differentiation in bovine fetuses

The temporal relationships between thyroid status and differentiation of liver, heart and different skeletal muscles were examined in 42 bovine fetuses from day 110 to day 260 of development using principal component analysis of the data. Plasma concentrations of reverse-triiodothyronine (rT(3)) and thyroxine (T(4)) increased during development from day 110 to day 210 or 260, respectively, whereas concentration of triiodothyronine (T(3)) and hepatic type-1 5'-deiodinase activity (5'D1) increased from day 180 onwards. On day 260, high T(4) and rT(3) and low T(3) concentrations were observed together with a mature 5'D1 activity. Cytochrome-c oxidase (COX) activity expressed per mg protein increased at day 180 in masseter and near birth in masseter, rectus abdominis and cutaneus trunci muscles (P<0.05). Significant changes in citrate synthase (CS) activity per mg protein were observed between day 110 and day 180 in the liver and between day 210 and day 260 in the liver, the heart and the longissimus thoracis muscle (P<0.05). Muscle contractile differentiation was shown by the disappearance of the fetal myosin heavy chain from day 180 onwards. A positive correlation (r>0.47, P<0.01) was shown between thyroid status parameters (5'D1, concentrations of T(4) and T(3)) and COX activity in muscles known to be oxidative after birth (masseter, rectus abdominis) but not in liver and heart, nor in muscles known to be glycolytic after birth (cutaneus trunci, longissimus thoracis). A similar correlation was found between thyroid parameters and CS activity in liver and masseter. Results indicate that elevation of plasma T(3) concentrations in the last gestational trimester could be involved in the differentiation of oxidative skeletal muscles.

Glucose-6-phosphate dehydrogenase and leptin are related to marbling differences among Limousin and Angus or Japanese Black x Angus steers

This work investigated the metabolic basis for the variability of carcass and i.m. adiposity in cattle. Our hypothesis was that the comparison of extreme breeds for adiposity might allow for the identification of some metabolic pathways determinant for carcass and i.m. adiposity. Thus, 23- to 28-mo-old steers of 3 breeds, 2 with high [Angus or Japanese Black x Angus (J. Black cross)] and 1 with low (Limousin) i.m. and carcass adiposity, were used to measure activities or mRNA levels, or both, of enzymes involved in de novo lipogenesis [acetyl-coA carboxylase, fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase (G6PDH), malic enzyme], circulating triacylglycerol (TAG) uptake (lipoprotein lipase), and fatty acid esterification (glycerol-3-phosphate dehydrogenase), as well as the mRNA level of leptin, an adiposity-related factor. In a first study, enzyme activities were assayed in the s.c. adipose tissue (AT), the oxidative rectus abdominis, and the glycolytic semitendinosus muscles from steers finished for 6 mo. Compared with Angus or J. Black cross, Limousin steers had a 27% less (P = 0.003) rib fat thickness, and 23 and 29% less (P < or = 0.02) FAS and G6PDH activities in s.c. AT. In rectus abdominis and semitendinosus, the 75% less (P < 0.001) TAG content was concomitant with 50% less (P < 0.001) G6PDH activity. In a second study, enzyme activities plus mRNA levels were assayed in an oxido-glycolytic muscle, the longissimus thoracis (LT), in the i.m. AT dissected from LT, and in s.c. AT from the same Limousin steers and from Angus steers finished for 10 mo. Compared with Angus, the 50% less (P < 0.001) rib fat thickness in Limousin contrasted with the 1.1- to 5.8-fold greater (P < or = 0.02) mRNA levels or activities, or both, of acetyl-coA carboxylase, G6PDH, lipoprotein lipase, and glycerol-3-phosphate dehydrogenase in s.c. AT. Conversely, the 90% less (P < 0.001) TAG content in Limousin LT was concomitant to the 79 and 83% less (P < or = 0.002) G6PDH activity and leptin mRNA level. Such differences could arise from a greater number of adipocytes in LT from Angus steers because no difference was found between Limousin and Angus for G6PDH activity and leptin mRNA in i.m. AT. We conclude that FAS and G6PDH in s.c. AT could be involved in differences in carcass adiposity, but this relationship disappeared when the fatness increased strongly. Leptin and G6PDH are related to the expression of marbling whatever the body condition and thus could be relevant indicators of marbling in beef cattle.

Performance, slaughter characteristics and meat quality of young bulls from Belgian Blue, Limousin and Aberdeen Angus breeds fattened with a sugar-beet pulp or a cereal-based diet

Thirty-six young fattening bulls from three breeds (Belgian Blue, Limousin and Aberdeen Angus) were fattened over 5 months with fattening diets based either on sugar-beet pulp or on cereals. Fattening performance as well as carcass and meat characteristics were measured. There were few relevant effects of the diets on the parameters. The breeds also showed similar fattening features. However, the BB had higher killing-out proportion and their carcasses presented better scores in terms of conformation and fattening. The meat quality of the breeds differed, especially in terms of luminosity, redness and cooking losses. There were also significant influences of breed on the chemical composition of meat; fat content was lowest in Belgian Blue and highest in Aberdeen Angus. Such specificities could help to allocate breeds in appropriate niches in Belgium.

Assessing the quality of products from cloned cattle: An integrative approach

Scientific expertise was developed during a 3-year study to evaluate a large number of bovine female clones (n=37; from 4 to 36 months of age) and their products through a multidisciplinary approach and compare them to non-cloned breed, age and sex-matched contemporary control animals (n=38) maintained under the same conditions at the same experimental farm of INRA. In clone and control groups, most parameters measured for health and development of the animals as well as evaluation of milk and meat products were within the normal range for the breed. The strict comparison between cloned animals and controls allowed us to detect slight significant differences between the two groups. Cloned heifers reached puberty significantly later (+62 days) and at higher body weight (+56kg) than controls. There were slight differences in antigen-specific induced proliferation of lymphocytes after vaccination with ovalbumin before 10 months of age, but responses were normal responses in older animals. There were differences in the fatty acid (FA) composition of milk and muscle arising from two families of clones, suggesting a possible deviation in lipid metabolism as assessed by higher Delta-9 desaturase activity indices in both milk and muscle from clones compared to controls. Nutritional evaluation of milk and meat using the rat model did not reveal any difference between products derived from clones versus controls.

Where are we in genomics?

Genomic studies provide scientists with methods to quickly analyse genes and their products en masse. The first high-throughput techniques to be developed were sequencing methods. A great number of genomes from different organisms have thus been sequenced. Genomics is now shifting to the study of gene expression and function. In the past 5-10 years genomics, proteomics and high-throughput microarray technologies have fundamentally changed our ability to study the molecular basis of cells and tissues in health and diseases, giving a new comprehensive view. For example, in cancer research we have seen new diagnostic opportunities for tumour classification, and prognostication. A new exciting development is metabolomics and lab-on-a-chip techniques (which combine miniaturization and automation) for metabolic studies. However, to interpret the large amount of data, extensive computational development is required. In the coming years, we will see the study of biological networks dominating the scene in Physiology. The great accumulation of genomics information will be used in computer programs to simulate biologic processes. Originally developed for genome analysis, bioinformatics now encompasses a wide range of fields in biology from gene studies to integrated biology (i.e. combination of different data sets from genes to metabolites). This is systems biology which aims to study biological organisms as a whole. In medicine, scientific results and applied biotechnologies arising from genomics will be used for effective prediction of diseases and risk associated with drugs. Preventive medicine and medical therapy will be personalized. Widespread applications of genomics for personalized medicine will require associations of gene expression pattern with diagnoses, treatment and clinical data. This will help in the discovery and development of drugs. In agriculture and animal science, the outcomes of genomics will include improvement in food safety, in crop yield, in traceability and in quality of animal products (dairy products and meat) through increased efficiency in breeding and better knowledge of animal physiology. Genomics and integrated biology are huge tasks and no single lab can pursue this alone. We are probably at the end of the beginning rather than at the beginning of the end because Genomics will probably change Biology to a greater extent than previously forecasted. In addition, there is a great need for more information and better understanding of genomics before complete public acceptance.

Immunohistochemical analysis of bFGF, TGF-beta1 and catalase in rectus abdominis muscle from cattle foetuses at 180 and 260 days post-conception

The potential for muscle growth depends on myoblast proliferation, which occurs essentially during the first two thirds of the foetal period in cattle. Thereafter, myofibres acquire their contractile and metabolic properties. Proliferation is regulated by molecular growth factors and by the tissue oxidative activity. The aim of this study was the quantification by immunochemistry of basic fibroblast growth factor (bFGF) and transforming growth factor beta 1 (TGF-beta1) and also of enzyme catalase (CAT) activity in rectus abdominis muscle. Samples were collected from cattle foetuses of different growth potential at 180 and 260 days post-conception (dpc). One major conclusion from this work is that protein contents of the muscle tissue bFGF and, to a lower extent, CAT activity decreased with increasing age during the foetal life. No differences were found between the different genotypes of cattle. However, the CAT to bFGF ratio tended to be lower in fast-growing cattle and increased with foetal age. TGF-beta1 did not change with age and was localised mostly at the vascular bed. CAT was detected in smooth and rough reticulum in striated muscles at 180dpc, and additionally in mitochondria at 260dpc. In conclusion, the balance between intracellular growth factors (bFGF and TGF-beta1) and the activity of antioxidant enzyme CAT may participate in the regulation of the transition from myoblast proliferation to differentiation. Thus, increased ratio of CAT to bFGF might be a good index indicating initiation of muscle maturation in cattle foetus prior to birth.

Weaning affects lipoprotein lipase activity and gene expression in adipose tissues and in masseter but not in other muscles of the calf

The nutritional and physiological modifications that occur during the weaning period induce adaptations of tissue metabolism in all mammal species. Among the adaptations due to weaning in ruminants, the regulation of lipoprotein lipase (LPL) activity, one of the rate-limiting steps of fatty acid utilization by tissues, was still unknown. The present study aimed at comparing LPL activity and gene expression in the heart, seven skeletal muscles and three adipose tissue sites between two groups of seven preruminant (PR) or ruminant (R) calves having a similar age (170 d), similar empty body weight (194 kg) at slaughter, and similar net energy intake from birth onwards. Triacylglycerol content of adipose tissues was 16 % lower in R than in PR calves, This could be partly the result from a lower LPL activity (-57 %, ). LPL mRNA levels were also lower in R calves (-48 % to -68 %, ) suggesting a pretranslational regulation of LPL activity. Activity and mRNA levels of LPL did not differ significantly in the heart and skeletal muscles except in the masseter in which LPL activity and mRNA levels were higher (+50 % and +120 % respectively, ) in the R calves. Regulation of LPL in masseter could be explained by the high contractile activity of this muscle after weaning due to solid food chewing. In conclusion, weaning in the calf affects LPL activity and expression in adipose tissues, but not in skeletal muscles except the masseter.

Effect of nutritional factors on biochemical, structural and metabolic characteristics of muscles in ruminants, consequences on dietetic value and sensorial qualities of meat

Ruminant meat is an important source of nutrients and is also of high sensory value. However, the importance and nature of these characteristics depend on ruminant nutrition. The first part of this review is focused on biochemical and dietetic value of this meat. It offers a panel of quantitative and qualitative contributions, especially through its fatty acids characteristics. Since saturated and trans-monounsaturated fatty acids are considered as harmful to human health, their amount in muscles can be reduced by increasing the proportions of dietary polyunsaturated fatty acids (PUFA) absorbed by the animals. On the contrary, some fatty acids (n-6 and n-3 PUFA, conjugated linoleic acid) specifically incorporated in muscle tissues would play a favourable role in the prevention or reduction of major diseases in human (cancers, atherosclerosis, obesity) and therefore be recommended. The second part of this review treats different aspects of the sensorial qualities of meat. Skeletal muscle structure and its biochemical components influence muscle transformation to meat and sensorial qualities including tenderness, colour, flavour and juiciness. This paper shows how nutrition can influence, in ruminants, metabolic activity as well as muscle structure and composition, and thereby affect meat quality.

Muscle fatty acid oxidative capacity is a determinant of whole body fat oxidation in elderly people

In sedentary elderly people, a reduced muscle fatty acid oxidative capacity (MFOC) may explain a decrease in whole body fat oxidation. Eleven sedentary and seven regularly exercising subjects (65.6 +/- 4. 5 yr) were characterized for their aerobic fitness [maximal O(2) uptake (VO(2 max))/kg fat free mass (FFM)] and their habitual daily physical activity level [free-living daily energy expenditure divided by sleeping metabolic rate (DEE(FLC)/SMR)]. MFOC was determined by incubating homogenates of vastus lateralis muscle with [1-(14)C]palmitate. Whole body fat oxidation was measured by indirect calorimetry over 24 h. MFOC was 40.4 +/- 14.7 and 44.3 +/- 16.3 nmol palmitate. g wet tissue(-1). min(-1) in the sedentary and regularly exercising individuals, respectively (P = nonsignificant). MFOC was positively correlated with DEE(FLC)/SMR (r = 0.58, P < 0. 05) but not with VO(2 max)/kg FFM (r = 0.35, P = nonsignificant). MFOC was the main determinant of fat oxidation during all time periods including physical activity. Indeed, MFOC explained 19.7 and 30.5% of the variance in fat oxidation during walking and during the alert period, respectively (P < 0.05). Furthermore, MFOC explained 23.0% of the variance in fat oxidation over 24 h (P < 0.05). It was concluded that, in elderly people, MFOC may be influenced more by overall daily physical activity than by regular exercising. MFOC is a major determinant of whole body fat oxidation during physical activities and, consequently, over 24 h.

Facilitative glucose transporters in livestock species

The study of facilitative glucose transporters (GLUT) requires carefully done immunological experiments and sensitive molecular biology approaches to identify the various mechanisms which control GLUT expression at the RNA and protein levels. The cloning of species-specific GLUT cDNAs showed that GLUT4 and GLUT1 diverge less among species than other GLUT isoforms. The key role of GLUT in glucose homeostasis has been demonstrated in livestock species. In vitro studies have suggested specific roles of GLUT1 and GLUT3 in avian cells. In vivo studies have demonstrated a regulation of GLUTs (especially of GLUT4) by nutritional and hormonal factors in pigs and cattle, in lactating cows and goats and throughout the foetal life in the placenta and tissues of lambs and calves. All these results suggest that any changes in GLUT expression and activity (such as GLUT4 in muscles) could modify nutrient partitioning and tissue metabolism, and hence, the qualities of animal products (milk, meat).

Age-related changes and location of types I, III, XII and XIV collagen during development of skeletal muscles from genetically different animals

The ontogenesis of total collagen and of different collagen types was studied in four muscle types from genetically different cattle. Hydroxyproline content was 1.2-fold higher in muscles from cross-bred foetuses with normal muscle growth compared to those of the other genetic types (pure bred with different growth rates, double-muscled breed). A similar tendency was observed for type III collagen content. In all muscles of each animal studied, type XII and XIV collagens were colocated in perimysium. Immunolabelling obtained for type XII collagen was higher during foetal life than after birth, while for type XIV collagen, the opposite result was obtained. Whatever the muscle studied, but especially in semitendinosus muscle, during the foetal and the post-natal period until 15 months of age, immunolabelling with antibody anti-type XIV collagen tended to be more intense in muscles of animals from fathers selected for a low muscle growth capacity compared to those from fathers selected for a high muscle growth capacity. In conclusion, this study shows, that during foetal life, selection according to muscle growth capacity has no significant effect on the contents of total hydroxyproline or type III collagen, but minor effects on collagen localization.

Lipoprotein lipase activity and mRNA are up-regulated by refeeding in adipose tissue and cardiac muscle of sheep

Previous studies in rodents have shown that the lipoprotein lipase (LPL) regulation is complex and often opposite in adipose tissue (AT) and muscle in response to the same nutritional treatment. However, neither LPL responses nor the molecular mechanisms involved in the nutritional regulation have been studied in both AT and muscle of ruminant species. To explore this, we measured the LPL activity and mRNA levels in perirenal AT and cardiac muscle (CM) of control, 7-d-underfed or 14-d-refed ewes. Underfeeding decreased (P < 0.01) LPL activity both in AT (-59%) and CM (-31%), and these activities were restored (P < 0.01) by refeeding (AT, +248%; CM, +34%). Variations of LPL mRNA level measured by real-time reverse transcription-polymerase chain reaction or by Northern blot followed variations of LPL activity: underfeeding decreased AT- and CM-LPL mRNA levels (-58 and -53%, respectively), and refeeding restored (P < 0.01) them in CM (+117%) and increased them over the baseline in AT (+640%). Quantification of either 3.4- or 3.8-kb LPL mRNA levels revealed a predominant (P < 0.001) expression of the 3.4-kb mRNA in AT (60%) and of the 3.8-kb mRNA in CM (56%), without any preferential regulation of one of these mRNA species by the nutritional status. This work reveals a tissue-specific expression pattern of the ovine LPL gene and a pretranslational nutritional regulation of its expression, which is achieved in the same direction in perirenal AT and CM. The different regulation of CM-LPL between ewes and rats probably arises from peculiarities of ruminant species for nutrient digestion and absorption and liver lipogenesis.

Dietary coconut oil affects more lipoprotein lipase activity than the mitochondria oxidative capacities in muscles of preruminant calves

The presence of coconut oil in a milk replacer stimulates the growth rate of calves, suggesting a better oxidation of fatty acid in muscles. Because dietary fatty acid composition influences carnitine palmitoyltransferase I (CPT I) activity in rat muscles, this study was designed to examine the effects of a milk replacer containing either tallow (TA) or coconut oil (CO) on fatty acid utilization and oxidation and on the characteristics of intermyofibrillar (IM) and subsarcolemmal (SS) mitochondria in the heart and skeletal muscles of preruminant calves. Feeding CO did not affect palmitate oxidation rate by whole homogenates, but induced higher palmitate oxidation by IM mitochondria (+37%, P < 0.05). CPT I activity did not significantly differ between the two groups of calves. Heart and longissimus thoracis muscle of calves fed CO had higher lipoprotein lipase activity (+27% and 58%, respectively; P < 0.05) but showed no differences in fatty acid binding protein content or activity of oxidative enzymes. Whatever the muscle and the diet, IM mitochondria had higher respiration rates and enzyme activities than those of SS mitochondria (P < 0.05). Furthermore, CPT I activity of the heart was 28-fold less sensitive to malonyl-coenzyme A inhibition in IM mitochondria than in SS mitochondria. In conclusion, dietary CO marginally affected the activity of the two mitochondrial populations and the oxidative activity of muscles in the preruminant calf. In addition, this study showed that differences between IM and SS mitochondria in the heart and muscles were higher in calves than in other species studied so far.

Effects of muscle type, castration, age, and compensatory growth rate on androgen receptor mRNA expression in bovine skeletal muscle

The effect of testosterone on sexual dimorphism is evident by differential growth of forelimb and neck muscles in bulls and steers. Divergent hormone sensitivites may account for the differential growth rates of individual muscles. Therefore, the objective of this study was to compare androgen receptor (AR) expression in three different muscles of bulls and steers at various ages and growth rates. Thirty Montbéliard bulls and 30 steers were assigned to four slaughter age groups. Four or five animals of each sex were slaughtered at 4 and 8 mo of age. Animals in the remaining two slaughter groups (12 and 16 mo) were divided into groups of either restricted (R) or ad libitum (AL) access to feed. Five animals of each sex and diet were slaughtered at the end of the restricted intake period at 12 mo of age. To simulate compensatory growth, the remaining animals (R and AL) were allowed ad libitum access to feed until slaughter at 16 mo of age. Total RNA was extracted from samples of semitendinosus (ST), triceps brachii (TB), and splenius (SP) muscles. Androgen receptor mRNA was quantified in 200-ng total RNA preparations using an internally standardized reverse transcription (RT) PCR assay. Data were analyzed using 18S ribosomal RNA concentrations as a covariable. Steers had higher AR mRNA levels per RNA unit than bulls (P < .01). Androgen receptor mRNA levels differed between muscles (P < .05), with lowest expression in the SP. The pattern of AR expression differed (P < .05) for each muscle with increasing age. Between 4 and 12 mo of age, AR mRNA levels increased (P < .05) in SP but remained unchanged in the ST and TB. Feeding regimen had no effect on muscle AR expression, but steers exhibiting compensatory growth had higher AR mRNA levels than AL steers (P < .01) or bulls (P < .01). Our results show that AR expression is muscle-specific and may be modulated by circulating testicular hormones. These data suggest that the regulation of AR expression may be linked to allometric muscle growth patterns in cattle and compensatory gain in steers.

Effects of dietary coconut oil on fatty acid oxidation capacity of the liver, the heart and skeletal muscles in the preruminant calf

The oxidative capacity of the liver, the heart and skeletal muscles for fatty acids were investigated in preruminant calves fed for 19 d on a milk-replacer containing either coconut oil (CO, rich in 12:0) or tallow (rich in 16:0 and 18:1). Weights of the total body and tissues did not differ significantly between the two groups of animals but plasma glucose and insulin concentrations were lower in the CO group. Feeding on the CO diet induced an 18-fold increase in the hepatic concentration of triacylglycerols. Rates of total and peroxisomal oxidation of [1-14C]laurate, [1-14C]palmitate and [1-14C]oleate were measured in fresh tissue homogenates. Higher rates of total oxidation in liver homogenate and of peroxisomal oxidation in liver, heart and rectus abdominis muscle homogenates were observed with laurate used as substrate. Furthermore, the relative contribution of peroxisomes to total oxidation was 1.9-fold higher in the liver and in the heart with laurate than with oleate or palmitate. Finally, the peroxisomal oxidation rate of oleate was 1.5-fold higher in the hearts of calves fed on the CO diet. Whatever the tissue, citrate synthase (CS, EC 4.1.3.7) and cytochrome c oxidase (COX, EC 1.9.3.1) activities were similar between the two groups of calves but the COX: CS activity ratio was lower in the liver of the CO group. In conclusion, laurate is better catabolized by peroxisomes than long-chain fatty acids, especially in the liver. Elongation of lauric acid after partial oxidation might explain the hepatic triacylglycerol accumulation in calves fed on the CO diet.

Fat partitioning and biochemical characteristics of fatty tissues in relation to plasma metabolites and hormones in normal and double-muscled young growing bulls

Plasma metabolites and hormones, and the biochemical characteristics of four fatty tissues (FT) were studied in two groups of six normal (N) or six double-muscled (DM) Belgian Blue young growing bulls fed the same net energy amount at the same live weight and slaughtered at 10 months of age. Average daily gain and feed efficiency did not significantly differ between the two groups. However, the DM bulls exhibited a higher proportion of muscles (+22%, P < 0.01) and a reduced proportion of fat (-49%, P < 0.01) mainly in the subcutaneous FT (-80%, P < 0.05). Triiodothyronine, insulin and glucose plasma concentrations tended to be lower in DM bulls (-24%, P < 0.02; -27%, P = 0.14; -7%, P = 0.06, respectively) and were positively related to the higher fat development in N bulls. From the results of total protein. DNA, lipid and TG contents of FT, it appeared that a reduction in fat storage per fat cell (hypotrophy) or a reduction in total fat cell number (hypoplasia) could explain, in DM bulls, two-thirds and one-third of the reduction of perirenal and subcutaneous FT weights, respectively, as compared to N bulls. In contrast, either hypotrophy or hypoplasia was the main cause of omental or intermuscular FT weight reduction in DM animals.

Intestinal absorption, blood transport and hepatic and muscle metabolism of fatty acids in preruminant and ruminant animals

Current research on lipid metabolism in ruminants aims to improve the growth and health of the animals and the muscle characteristics associated with meat quality. This review, therefore, focuses on fatty acid (FA) metabolism from absorption to partitioning between tissues and metabolic pathways. In young calves, which were given high-fat milk diets, lipid absorption is delayed because the coagulation of milk caseins results in the retention of dietary fat as an insoluble clot in the abomasum. After weaning, the calves were fed forage- and cereal-based diets containing low levels of long-chain fatty acids (LCFA) but leading to high levels of volatile fatty acid (VFA) production by the rumen microflora. Such differences in dietary FA affect: i) the lipid transport system via the production of lipoproteins by the intestine and the liver, and (ii) the subsequent metabolism of lipids and FA by tissues. In preruminant calves, high-fat feed stimulates the secretion of triacylglycerols (TG)-rich lipoproteins (chylomicrons, very-low density lipoproteins (VLDL)). Diets rich in polyunsaturated FA (PUFA) stimulate the production of chylomicrons by the intestine (at peak lipid absorption) and of high density lipoproteins by the liver, leading to high blood concentrations of cholesterol. High levels of non-esterified FA (NEFA) uptake by the liver in high-yielding dairy cows in early lactation leads to TG infiltration of the hepatocytes (fatty liver). This is due to the low chronic capacity of the liver to synthesise and secrete VLDL particles. This abnormality in hepatic FA metabolism involves defects in apolipoprotein B synthesis and low availability of apolipoproteins and lipids for VLDL packaging. Fatty liver in calves is also caused by milk containing either soybean oil (rich in n-6 PUFA), or coconut oil (rich in C12:0 and C14:0). The ability of muscle tissue to use FA as an energy source depends on its mitochondrial content and, hence, on many physiological factors. The uptake and partitioning of LCFA between oxidation and storage in muscle is regulated by the activity of key intracellular enzymes and binding proteins. One such protein, carnitine palmitoyltransferase I (CPT I) controls the transport of LCFA into mitochondria. Metabolites derived from LCFA inhibit glucose oxidation, decrease the activity of CPT I and decrease the efficiency of ATP production by mitochondria. Most research on tissue lipid metabolism in ruminants is focused on: i) the partitioning of FA oxidation between intracellular peroxisomes and mitochondria in the liver and in muscles; (ii) the regulation of lipid metabolism by leptin, a recently discovered hormone secreted by mature adipocytes; and iii) the effects of activation of the nuclear receptors (PPARs and RXR) by LCFA or by phytol metabolites derived from chlorophyll.

Lipoprotein lipase activity and mRNA levels in bovine tissues

Lipoprotein lipase (LPL) in cattle has been extensively studied in adipose tissue, milk and mammary gland, but only to a limited extent in muscles. Therefore, we have adapted our in vitro LPL assay method for the measurement of LPL activity and describe, for the first time, sensitive procedures to quantify LPL activity and mRNA levels in bovine muscles. In vitro activation of bovine LPL activity is approximately 5-fold greater with rat than with bovine sera for heart and muscles, but not for adipose tissues. Values of LPL activity are in the upper range of those previously reported for rat or bovine tissues. With rat serum as activator, LPL activity in the heart of seven calves (662-832 mU g-1) is at least 3-fold lower than in the rat heart (2150-2950 mU g-1, P < 0.05). LPL activity is higher in bovine heart and oxidative muscles (412-972 mU g-1), except the diaphragm, than in mixed or glycolytic muscles (33-154 mU g-1, P < 0.05). The levels of LPL transcripts are positively related to LPL activity in bovine tissues, including muscles and adipose tissues.

Contribution of mitochondria and peroxisomes to palmitate oxidation in rat and bovine tissues

Total and peroxisomal palmitate oxidation capacities and mitochondrial enzyme activities were compared in tissues from growing rats, preruminant calves and 15-month-old bulls. Total palmitate oxidation rates were 1.9-5.2-fold higher in rat than in bovine tissues and 1.7-fold higher in the heart and muscles from calves than from growing bulls. The peroxisomal contribution to palmitate oxidation was similar between rats and bovines (i.e. calves and bulls) in liver (35-51%), heart (26%) but not in muscles (14 +/- 3% in rats vs 33 +/- 4.5% in bovines, P < 0.05). Mitochondrial enzyme activities were 1.8-4.8-fold higher in rat than in bovine tissues but the citrate synthase to cytochrome-c oxidase ratio was the highest in the liver (17-38), intermediate in the heart and muscles from calves and rats (6-10) and the lowest in heart and muscles from bulls (2-3, P < 0.05). In all tissues and animal groups, palmitate oxidation rates were similar per unit cytochrome-c oxidase activity, but not always per unit citrate synthase activity. Therefore, differences in mitochondrial contents (as between rats and bovines) or in mitochondrial characteristics (as between liver and muscles) relate to the differences in palmitate oxidation capacity.

Acute hyperinsulinemia fails to change GLUT-4 content in crude membranes from goat skeletal muscles and adipose tissue

The effect of insulin on GLUT-4 protein level in samples of adipose tissue and skeletal muscles from goats was studied in vivo using an euglycemic hyperinsulinemic clamp. The clamp was maintained in conscious goats for 6 h in the presence of amino acids to prevent insulin-induced hypoaminoacidemia. GLUT-4 protein was assessed in crude membrane preparations from adipose tissue and four skeletal muscles (longissimus dorsi, tensor fasciae latae, anconeus and diaphragm) by Western blot analysis. No changes of GLUT-4 protein content were detected after 6 h of hyperinsulinemia in either adipose tissue or skeletal muscles from goats. These results suggest that insulin is not the prime factor involved in the short-term regulation of GLUT-4 protein transporter content in insulin-sensitive tissues from goats.

Messenger RNAs encoding lipoprotein lipase, fatty acid synthase and hormone-sensitive lipase in the adipose tissue of underfed-refed ewes and cows

The mechanisms involved in the nutritional regulation of genes encoding lipogenic (lipoprotein lipase (LPL) and fatty acid synthase (FAS)) and lipolytic (hormone-sensitive lipase (HSL)) enzymes were investigated by comparing the levels of the corresponding mRNAs in the adipose tissue (AT) of underfed or underfed-refed ewes and cows. Refeeding sharply increased LPL and FAS activities (19-25- and 6-8-fold, respectively) and moderately increased (2-4 fold) the activities of glucose-6-phosphate dehydrogenase (G6PDH), malic enzyme (ME) and glycerol-3-phosphate dehydrogenase (G3PDH). Northern blot analysis revealed three LPL transcripts and a single FAS transcript in cow and ewe AT. A single HSL mRNA was detected in cow AT and two transcripts in ewe AT. Refeeding sharply increased LPL and FAS mRNA levels, while restriction slightly increased (cows) or had no effect (ewes) on the HSL mRNA levels. This suggests that nutritional factors regulate sharply the expression of LPL and FAS genes by pretranslational mechanisms, but less clearly that of HSL gene.

Weaning marginally affects glucose transporter (GLUT4) expression in calf muscles and adipose tissues

The nutritional regulation of glucose transporter GLUT4 was studied in eight muscles and four adipose tissues from two groups of preruminant (PR) or ruminant (R) calves of similar age (170 d), empty body weight (194 kg) at slaughter, and level of net energy intake from birth onwards. Isocitrate dehydrogenase (EC 1.1.1.41) activity in muscles was not different between PR and R except in masseter muscle from the cheek (+71% in R; P < 0.003), which becomes almost constantly active at weaning for food chewing. Basal and maximally-insulin-stimulated glucose transport rate (GTR) per g tissue wet weight in rectus abdominis muscle were significantly higher in R calves (+31 and 41% respectively; P < 0.05). GLUT4 protein contents did not differ in muscles from PR and R except in masseter (+74% in R; P < 0.05) indicating that the increased GTR in rectus abdominis cannot be accounted for by an enhanced GLUT4 expression. GLUT4 mRNA levels did not differ between the two groups of animals in all muscles suggesting a regulation of GLUT4 at the protein level in masseter. GLUT4 number expressed on a per cell basis was lower in adipose tissue from R calves (-39%; P < 0.05) and higher in internal than in peripheral adipose tissues. In summary, the regulation of GLUT4 in calves at weaning differs markedly from that previously described in rodents (for review, see Girard et al. 1992). Furthermore, significant inter-individual variations were shown for metabolic activities in muscle and for biochemical variables in adipose tissue.

Insulin-sensitive glucose transporter transcript levels in calf muscles assessed with a bovine GLUT4 cDNA fragment

Previous studies have shown that the expression of the insulin-sensitive glucose transporter (GLUT4) is lower in oxidative muscles than in glycolytic muscles in bovines and goats in contrast to observations in rats. Additional experiments in this work provide very strong arguments that the immunoreactive band detected does represent GLUT4 protein, which further validates our previous results. Therefore, to determine the level of regulation, the main objective of the present study was to measure GLUT4 mRNA amounts in various bovine muscles. A 241-bp fragment of the bovine GLUT4 cDNA was cloned by polymerase chain reaction (PCR). It shares 80-90% sequence identity with related sequences in other species. This PCR-amplified bovine GLUT4 probe was used to determine the distribution of GLUT4 mRNA in bovine tissues in comparison with that of GLUT1 mRNA. Moreover, GLUT4 mRNA amounts were quantified by Northern-blot analysis in heart and seven skeletal muscles with various oxidative and glycolytic activities from seven ruminant calves. GLUT4 mRNA was detected by Northern-blot analysis only in calf insulin-sensitive tissues. In contrast, GLUT1 mRNA was detected in all tissues studied except liver. GLUT4 mRNA amount was the highest in masseter and heart, which are oxidative muscles (1.67 +/- 0.16 and 1.53 +/- 0.19 units/g wet tissue weight, respectively) and the lowest in glycolytic or oxido-glycolytic muscles (0.31 +/- 0.04 to 1.00 +/- 0.09 units/g wet tissue weight; SEM, n = 7). These data and our previous results provide evidence for translational and/or post-translational control mechanisms of bovine GLUT4 protein expression in a muscle type-specific manner.

Glucose-transporter (GLUT4) protein content in oxidative and glycolytic skeletal muscles from calf and goat

It is well accepted that skeletal muscle is a major glucose-utilizing tissue and that insulin is able to stimulate in vivo glucose utilization in ruminants as in monogastrics. In order to determine precisely how glucose uptake is controlled in various ruminant muscles, particularly by insulin, this study was designed to investigate in vitro glucose transport and insulin-regulatable glucose-transporter protein (GLUT4) in muscle from calf and goat. Our data demonstrate that glucose transport is the rate-limiting step for glucose uptake in bovine fibre strips, as in rat muscle. Insulin increases the rate of in vitro glucose transport in bovine muscle, but to a lower extent than in rat muscle. A GLUT4-like protein was detected by immunoblot assay in all insulin-responsive tissues from calf and goat (heart, skeletal muscle, adipose tissue) but not in liver, brain, erythrocytes and intestine. Unlike the rat, bovine and goat GLUT4 content is higher in glycolytic and oxido-glycolytic muscles than in oxidative muscles. In conclusion, using both a functional test (insulin stimulation of glucose transport) and an immunological approach, this study demonstrates that ruminant muscles express GLUT4 protein. Our data also suggest that, in ruminants, glucose is the main energy-yielding substrate for glycolytic but not for oxidative muscles, and that insulin responsiveness may be lower in oxidative than in other skeletal muscles.

Study of the influence of age and weaning on the contractile and metabolic characteristics of bovine muscle

Weaning is an interesting period for the study of the nutritional regulation of muscle energy metabolism, since during this stage the nature of the substrates supplied to the muscle and their energy balance are profoundly changed. The aim of this study was to determine the effect of these modifications on the contractile and metabolic characteristics of bovine muscle. Two similar groups of 7 male Montbéliard calves were used with the same age and weight, and with the same energy intake. One group consisted of milk-fed calves, the other of weaned animals. The latter were progressively weaned over a period between 107 and 128 d. The average age at slaughter in the 2 groups was 170 d. Biopsy specimens of semitendinosus (ST) muscle were taken at the ages of 66 d, 94 d (before the beginning of weaning) and 136 d (at the end of weaning) to follow the evolution of muscle characteristics. Samples of longissimus thoracis (LT) muscle were taken 24 h after slaughter and used to study the changes in protein and DNA content. The proportion and area of the different types of fiber, I (slow, oxidative), IIA (fast, oxido-glycolytic), IIB (fast, glycolytic) and IIC (fast/slow, oxidoglycolytic) were measured by immunohistochemistry and image analysis. The metabolism of the muscles was determined by studying isocitrate dehydrogenase (ICDH, oxidative) and lactate dehydrogenase (LDH, glycolytic) activity. The results obtained between 2 and 6 months of life showed an overall increase in the area of the fibers (I, IIA, IIB and IIC) and a conversion of type IIA fibers into type IIB accompanied by a shift in the energy metabolism towards a glycolytic type. Weaning caused temporary stress, whose main consequences were to decrease overall muscle fiber area and the percentage of type IIB fibers, and increase the proportion of type IIC fibers in weaned animals. These effects may have been due to the nutritional and behavioral disturbances that accompany weaning, because 42 d after the end of weaning there was no difference in the size of ST and LT fibers between the 2 groups whereas the proportion of type IIA fibers was still higher in weaned animals.

[Analysis of human growth hormone-binding protein in plasma by high pressure liquid chromatography]

A technique using high pressure liquid chromatography gel filtration was used to evaluate GH-binding proteins (GH-BPs) in human plasma; eluate was monitored for radioactivity in a gamma-detection system connected to a computer. Plasma (200 microliters) was incubated with 125I-human (h) GH (200,000 cpm) at 4 degrees C for 20 hours. Our GH binding assay offers important gains in terms of rapidity and resolution; it has permitted a clear separation and characterization of the two GH-binding components present in human plasma.

Human plasma growth hormone (GH)-binding proteins are regulated by GH and testosterone

Possible regulation of GH-binding proteins (GH-BPs) in human plasma was examined. Eight children with isolated GH deficiency had a very low level of plasma GH-binding activity (10.2 +/- 1.1% of radioactivity). Under GH treatment the hormone binding to the high affinity BP (peak II-BP) increased in every patient to reach the mean value of 18.5 +/- 1.4%. In one patient, Scatchard plot analysis indicated that this increase was related to a higher binding capacity without any significant change in the binding affinity. A positive correlation existed between the GH-binding activity and insulin-like growth factor-I plasma levels. In nine boys with pubertal delay, the GH-specific binding to peak II-BP was normal (30.6 +/- 3.7% of radioactivity); it decreased significantly after testosterone treatment. In four boys with precocious puberty, the specific GH binding to peak II-BP was low (16.6 +/- 1.1%). It increased significantly to 21.6 +/- 1.1% of radioactivity after treatment with a LHRH analog. A negative correlation existed between plasma testosterone levels and GH binding to peak II-BP in boys presenting pubertal delay or precocious puberty. The high affinity GH-BP is regulated, and among the factors that play a role in this regulation, GH and testosterone have opposite effects.

Evaluation of the growth hormone-binding proteins in human plasma using high pressure liquid chromatography gel filtration

A technique using high pressure liquid chromatography gel filtration was used to evaluate GH-binding proteins (BP) in human plasma; eluate was monitored for radioactivity in a gamma-detection system connected to a computer. Plasma (200 microL) was incubated with [125I]human (h) GH (200,000 cpm) at 4 C for 20 h. The main GH-BP (peak II) was well separated from free [125I]hGH (peak III) and from a higher mol wt complex (peak I), which was minor. In our control plasma, the specific binding of [125I]hGH to peak II BP (II-BP) was 32.2 +/- 0.6% of the radioactivity. Scatchard analyses indicate an association constant of 3.6-7.4 X 10(8) M-1 and a binding capacity ranging from 24-86 ng/mL for peak II-BP in five normal adult plasma samples. Peak I material, separated from plasma of boys with pubertal delay, bound hGH with a low affinity (3 x 10(6) M-1) and a very high capacity (2 micrograms/mL). In cross-linking experiments, peak I appeared as two proteins of 165 and 174 kD; these mol wt were much higher than that of peak II-BP, previously estimated at 53,000. hGH complexed to peak II-BP remained fully immunoreactive with use of the anti-hGH antibodies of our assay. In plasma containing 10-20 micrograms/L hGH, the proportion of bound hormone (peak II) was 44.5 +/- 2.3%, whereas the amount of hGH in peak I was very low or undetectable. Specific binding of hGH to II-BP was lowest during the first year of life and highest in adulthood. No sex difference was found. I-BP is differentially regulated, since its binding activity was significantly lower in adults than in prepubertal children. Normal values for age should be taken into account to interpret GH-binding activity, particularly in children 2 yr of age or younger. Our GH binding assay offers important gains in terms of rapidity and resolution; it has permitted a clear separation and characterization of the two GH-binding components present in human plasma.

Human liver growth hormone receptor and plasma binding protein: characterization and partial purification

The human liver GH receptor has been further characterized using several biochemical approaches. Crosslinking of [125 I]human GH (hGH) to microsomal receptors and to particulate and solubilized plasma membrane receptors, followed by gel electrophoresis and autoradiography, revealed two predominant receptor-hormone complexes with a mol wt of 124,000 and 75,000, respectively. As previously shown, the 70-80 k band appears to be generated from the 124 k band in the presence of beta-mercaptoethanol, suggesting intersubunit disulfide linkages. A minor complex of mol wt 150,000 was sometimes found. By immunoblot, using a polyclonal antibody raised against a synthetic peptide (residues 391-405 of the mature human GH receptor), a single band of 100 k was detected. Human liver GH receptor and plasma GH-binding protein (BP) were purified 1,000- and 4,000-fold, respectively. The partially purified membrane receptor, analyzed by ligand-blot, showed two major bands of 55 and 32 k and minor bands of 68 and 47 k. Crosslinking of the purified GH-BP or purified receptor with [125I]hGH revealed a 75 k receptor-hormone complex. Polyclonal antibodies raised against the hepatic GH receptor inhibited the binding of hGH to the human receptor and were able to immunoprecipitate the GH receptor and also the GH-BP complex. Our findings demonstrate the existence of multiple forms of the GH receptor in human liver (major components of 100 and 50-55 k, minor component of 130 k); they lend more support to the possible subunit structure of the GH receptor; and finally, they also suggest a close relationship, with common antigenic properties, of the membrane receptor and the plasma GH-BP.

The human liver growth hormone receptor

Human livers, obtained from donors at the time of transplant, were homogenized in 0.25 M sucrose and fractionated by differential centrifugation. The specific binding of [125I] human (h) GH to total particulate fractions from 18 livers varied from 0.4-5.1% of the total radioactivity/100 micrograms protein. Binding affinity was 2.0 +/- 0.3 X 10(9) M-1, and binding capacity ranged from 14-53 fmol/mg protein. A different proportion of receptors occupied by endogenous hGH did not explain the large variation in binding. Binding sites were specific for hGH. Dissociation of the hormone-receptor complex was extremely slow. No specific binding of [125I]hPRL was observed. Specific binding of insulin was found in fractions from all livers and varied less than hGH binding. Cross-linking of [125I]hGH to plasma membrane and microsome receptors yielded two major autoradiographic bands corresponding to an estimated mol wt of 103,000 for the receptor, with a possible subunit of 54,000. Human liver primary fractions were characterized. The binding of hGH and insulin displayed a nucleo-microsomal distribution pattern in the primary fractions; 54.2% and 27.9% of the hGH-binding activity were found in the microsomes and the nuclear fraction, respectively, whereas insulin binds equally to nuclear and microsomal elements. Our findings suggest that hGH-binding sites are present in the plasma membrane and also in one or more intracellular compartments, whereas a high proportion of insulin receptors is associated with the plasma membrane.