Effects of divergent selection for body weight on three skeletal muscles characteristics in the chicken

Research progress on regulating factors of muscle fiber heterogeneity in poultry: a review

Control of meat quality traits is an important goal of any farm animal production, including poultry. A better understanding of the biochemical properties of muscle fiber properties that drive muscle development and ultimately meat quality constitutes one of the major challenging topics in animal production and meat science. In this paper, the existing classification methods of skeletal muscle fibers in poultry were reviewed and the relationship between contractile and metabolic characteristics of muscle fibers and poultry meat quality was described. Finally, a comprehensive review of multiple potential factors affecting muscle fiber distribution and conversion is presented, including breed, sex, hormones, growth performance, diet, muscle position, exercise, and ambient temperature. We emphasize that knowledge of muscle fiber typing is essential to better understand how to control muscle characteristics throughout the life cycle of animals to better manage the final quality of poultry meat.

Genetic architecture of white striping in turkeys (Meleagris gallopavo)

White striping (WS) is a myopathy of growing concern to the turkey industry. It is rising in prevalence and has negative consequences for consumer acceptance and the functional properties of turkey meat. The objective of this study was to conduct a genome-wide association study (GWAS) and functional analysis on WS severity. Phenotypic data consisted of white striping scored on turkey breast fillets (N = 8422) by trained observers on a 0-3 scale (none to severe). Of the phenotyped birds, 4667 genotypic records were available using a proprietary 65 K single nucleotide polymorphism (SNP) chip. The SNP effects were estimated using a linear mixed model with a 30-SNP sliding window approach used to express the percentage genetic variance explained. Positional candidate genes were those located within 50 kb of the top 1% of SNP windows explaining the most genetic variance. Of the 95 positional candidate genes, seven were further classified as functional candidate genes because of their association with both a significant gene ontology and molecular function term. The results of the GWAS emphasize the polygenic nature of the trait with no specific genomic region contributing a large portion to the overall genetic variance. Significant pathways relating to growth, muscle development, collagen formation, circulatory system development, cell response to stimulus, and cytokine production were identified. These results help to support published biological associations between WS and hypoxia and oxidative stress and provide information that may be useful for future-omics studies in understanding the biological associations with WS development in turkeys.

A critical review of the mechanisms involved in the occurrence of growth-related abnormalities affecting broiler chicken breast muscles

In the past decade, the poultry industry has faced the occurrence of growth-related muscular abnormalities that mainly affect, with a high incidence rate, the Pectoralis major of the fast-growing genotypes selected for their production performances (high growth rate and breast yield). These myopathies are termed as White Striping, Wooden Breast, and Spaghetti Meat and exhibit distinctive phenotypes. A spatiotemporal distribution has been demonstrated for these disorders as in the early stage they primarily affect the superficial area in the cranial portion of the muscle and, as the birds grow older, involve the entire tissue. Aside from their distinctive phenotypes, these myopathies share common histological features. Thus, it might be speculated that common causative mechanisms might be responsible for the physiological and structural perturbations in the muscle associated with these conditions and might underpin their occurrence. The present review paper aims to represent a critical survey of the outcomes of all the histologic and ultrastructural observations carried out on White Striping, Wooden Breast, and Spaghetti Meat affected muscles. Our analysis has been performed by combining these outcomes with the findings of the genetic studies, trying to identify possible initial causative mechanisms triggering the onset and the time-series of the events ultimately resulting in the development and progression of the growth-related myopathies currently affecting broilers Pectoralis major muscles. Several evidences support the hypothesis that sarcoplasmic reticulum stress, primarily induced an accumulation of misfolded proteins (but also driven by other factors including altered calcium homeostasis and accumulation of fatty acids), may be responsible for the onset of these growth-related myopathies in broilers. At the same time, the development of hypoxic conditions, as a direct consequence of an inadequate vascularization, triggers a time-series sequence of events (i.e., phlebitis, oxidative stress, etc.) resulting in the activation of response mechanisms (i.e., modifications in the energetic metabolism, inflammation, degeneration, and regeneration) which are all strictly related to the progression of these myopathic disorders.

Fiber Metabolism, Procollagen and Collagen Type III Immunoreactivity in Broiler Pectoralis Major Affected by Muscle Abnormalities

The present study aimed to evaluate the muscle fiber metabolism and assess the presence and distribution of both procollagen and collagen type III in pectoralis major muscles affected by white striping (WS), wooden breast (WB), and spaghetti meat (SM), as well as in those with macroscopically normal appearance (NORM). For this purpose, 20 pectoralis major muscles (five per group) were selected from the same flock of fast-growing broilers (Ross 308, males, 45-days-old, 3.0 kg live weight) and were used for histochemical (nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR) and alpha-glycerophosphate dehydrogenase (α-GPD)) and immunohistochemical (procollagen and collagen type III) analyses. When compared to NORM, we found an increased proportion (p < 0.001) of fibers positively stained to NADH-TR in myopathic muscles along with a relevant decrease (p < 0.001) in the percentage of those exhibiting a positive reaction to α-GPD. In addition, an increased proportion of fibers exhibiting a positive reaction to both stainings was observed in SM, in comparison with NORM (14.3 vs. 7.2%; p < 0.001). After reacting to NADH-TR, SM exhibited the lowest (p < 0.001) cross-sectional area (CSA) of the fibers (-12% with respect to NORM). On the other hand, after reacting to α-GPD, the CSA of WS was found to be significantly larger (+10%) in comparison with NORM (7480 vs. 6776 µm2; p < 0.05). A profound modification of the connective tissue architecture involving a different presence and distribution of procollagen and collagen type III was observed. Intriguingly, an altered metabolism and differences in the presence and distribution of procollagen and collagen type III were even observed in pectoralis major muscle classified as NORM.

Energy metabolism and sources of oxidative stress in wooden breast - a review

Modern broilers show dramatic growth over a short interval and contribute directly to the success of the poultry meat industry. The growth performance of commercial broilers is a result of genetic selection for "performance traits", such as body size, meat yield, and feed conversion rate. However, due to the rapid growth rate of modern commercial broilers, several growth-related conditions have arisen, increasing economic losses and consumer concerns. Among the most economically consequential is the muscle disorder called wooden breast. Together with associated myopathies such as white striping and spaghetti meat, wooden breast is causing losses of $200 million a year in the U.S. alone and occurs worldwide. No causative factors are known for wooden breast to date. Wooden breast can affect over 80% of broilers in a flock, yet no methods of amelioration are currently available. Overall, the evidence suggests that wooden breast is a genetic, age-dependent condition associated with fast growth rate. The primary features of wooden breast are muscle degeneration and fibrosis, high levels of oxidative stress, hypoxia, and altered energy metabolism. Recent work has also implicated reduced pectoral vessel density in the pathogenesis of wooden breast. This review examines the history of myopathies in commercial broilers and the relationship of myopathies to metabolism and oxidative performance. This review summarizes the foundational knowledge of wooden breast and provides a platform for further investigation of wooden breast.

Performance and Meat Quality of Dual-Purpose Cockerels of Dominant Genotype Reared on Pasture

Simple Summary

One-day-old laying cockerels are killed after hatching because they do not reach the growth rate of broiler chickens, and their fattening would be economically disadvantageous. A possible variant of the use of these cockerels could be organic or free-range farming, where it is desirable that the animals are fattened for a longer period of time, are more physically active, and graze pasture vegetation. Another possibility is dual-purpose genotype breeding, where hens are used for egg production and cockerels are fattened for meat. In the present study, three genotypes of dual-purpose cockerels Dominant were compared. All three genotypes showed the ability to graze with resulting improvements in meat quality. The Dominant 102 cockerels have the greatest prerequisites for use in extensive fattening, mainly due to higher performance, willingness to graze and vitamin E content, which protects the fat from becoming rancid.

Abstract

The culling of layer cockerels due to economic inefficiency is an ethical problem. Organic or free-range fattening of these cockerels or dual-purpose genotypes breeding is a possible solution to this problem. The aim of the study was to assess the differences in performance and meat quality characteristics in dual-purpose cockerels Dominant of three genotypes (Dominant Sussex D 104, Dominant Brown D 102 and Dominant Tinted D 723, 100 cockerels per genotype) with access to pasture. The cockerels were housed in mobile boxes on the pasture herbage from the 50th to 77th day of age (stocking density: 0.108 m²/bird). The highest body weight on the 77th day of age (p < 0.001) and the nonsignificantly lowest feed conversion was achieved by Dominant Brown D 102 cockerels (1842 g and 2.79, respectively). Non-significantly higher pasture herbage intake on the 70th day of age was recorded in genotype Dominant Brown D 102 (7.41 g dry matter (DM)/bird/day) and Dominant Tinted D 723 (7.52 g DM/bird/day). The pasture herbage contained 56.9 mg/kg DM α-tocopherol, 170.3 mg/kg DM zeaxanthin and 175.0 mg/kg DM lutein and had a favourable n6/n3 ratio (0.26). The boiled meat of cockerels Dominant Tinted D723 showed the highest tenderness based on both the sensory evaluation (p = 0.022) and the value of shear force (p = 0.049). This corresponds with a higher (p < 0.001) cross-sectional area and muscle fibre diameter in these chickens. The highest content of n3 fatty acids (eicosapentaenoic, clupanodonic and docosahexaenoic acids) in breast meat were found in Dominant Sussex D104 chickens (p < 0.001). In contrast, a significantly higher α-tocopherol content (p < 0.001) and higher oxidative stability (p = 0.012) were found in Dominant Brown D102 (4.52 mg/kg and 0.282 mg/kg) and Dominant Tinted D 723 chickens (4.64 mg/kg and 0.273 mg/kg) in comparison with the Dominant Sussex D104 genotype (3.44 mg/kg and 0.313 mg/kg). The values of the atherogenic and thrombogenic indexes were the lowest (p < 0.001) in meat from Dominant Brown D102 chickens. Moreover, a lower cholesterol content (p < 0.001) was recorded from the genotypes Dominant Brown D102 (396 mg/kg) and Dominant Tinted D723 (306 mg/kg) chickens, contrary to the Dominant Sussex D104 cockerels (441 mg/kg). It can be concluded that cockerels Dominant Brown D102 are a suitable genotype for free-range rearing due to higher performance and higher pasture herbage intake, which positively influences meat quality, whereas the meat of Dominant Sussex D104 cockerels shows higher amounts of n3 fatty acids and lower n6/n3 ratios.

Transcriptional profiling and pathway analysis reveal differences in pituitary gland function, morphology, and vascularization in chickens genetically selected for high or low body weight

Background

Though intensive genetic selection has led to extraordinary advances in growth rate and feed efficiency in production of meat-type chickens, endocrine processes controlling these traits are still poorly understood. The anterior pituitary gland is a central component of the neuroendocrine system and plays a key role in regulating important physiological processes that directly impact broiler production efficiency, though how differences in pituitary gland function contribute to various growth and body composition phenotypes is not fully understood.

Results

Global anterior pituitary gene expression was evaluated on post-hatch weeks 1, 3, 5, and 7 in male broiler chickens selected for high (HG) or low (LG) growth. Differentially expressed genes (DEGs) were analyzed with gene ontology categorization, self-organizing maps, gene interaction network determination, and upstream regulator identification to uncover novel pituitary genes and pathways contributing to differences in growth and body composition. A total of 263 genes were differentially expressed between HG and LG anterior pituitary glands (P ≤ 0.05 for genetic line-by-age interaction or main effect of line; ≥1.6-fold difference between lines), including genes encoding four anterior pituitary hormones. Genes involved in signal transduction, transcriptional regulation, and vesicle-mediated transport were differentially expressed and are predicted to influence expression and secretion of pituitary hormones. DEGs involved in immune regulation provide evidence that inflammation and response to cellular stressors may compromise pituitary function in LG birds, affecting their ability to adequately produce pituitary hormones. Many DEGs were also predicted to function in processes that regulate organ morphology and angiogenesis, suggesting pituitary gland structure differs between the divergently selected lines.

Conclusions

The large number of DEGs within the anterior pituitary gland of birds selected for high or low body weight highlights the importance of this gland in regulating economically important traits such as growth and body composition in broiler chickens. Intracellular signaling, transcriptional regulation, and membrane trafficking are important cellular processes contributing to proper hormone production and secretion. The data also suggest that pituitary function is intimately tied to structure, and organization of the gland could influence hypothalamic and systemic metabolic inputs and delivery of hormones regulating growth and metabolism into peripheral circulation.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5670-9) contains supplementary material, which is available to authorized users.

Expression of glucose transporters SLC2A1, SLC2A8, and SLC2A12 in different chicken muscles during ontogenesis

Glucose transport into cells is the first limiting step for the regulation of glucose homeostasis. In mammals, it is mediated by a family of facilitative glucose transporters (GLUTs) (encoded by SLC2A* genes), with a constitutive role (GLUT1), or insulin-sensitive transporters (GLUT4, GLUT8, and GLUT12). Compared to mammals, the chicken shows high levels of glycemia and relative insensitivity to exogenous insulin. To date, only GLUT1, GLUT8, and GLUT12 have been described in chicken skeletal muscles but not fully characterized, whereas GLUT4 was reported as lacking. The aim of the present study was to determine the changes in the expression of the SLC2A1, SLC2A8, and SLC2A12 genes, encoding GLUT1, GLUT8, and GLUT12 proteins respectively, during ontogenesis and how the respective expression of these three genes is affected by the muscle type and the nutritional or insulin status of the bird (fed, fasted, or insulin immunoneutralized). SLC2A1 was mostly expressed in the glycolytic pectoralis major (PM) muscle during embryogenesis and 5 d posthatching while SLC2A8 was mainly expressed at hatching. SLC2A12 expression increased regularly from 12 d in ovo up to 5 d posthatching. In the mixed-type sartorius muscle, the expression of SLC2A1 and SLC2A8 remained unchanged, whereas that of SLC2A12 was gradually increased during early muscle development. The expression of SLC2A1 and SLC2A8 was greater in oxidative and oxidoglycolytic muscles than in glycolytic muscles. The expression of SLC2A12 differed considerably between muscles but not necessarily in relation to muscle contractile or metabolic type. The expression of SLC2A1, SLC2A8, and SLC2A12 was reduced by fasting and insulin immunoneutralization in the PM muscle, while in the leg muscles only SLC2A12 was impaired by insulin immunoneutralization. Our findings clearly indicate differential regulation of the expression of three major GLUTs in skeletal muscles, with some type-related features. They provide new insights to improve the understanding of the fine regulation of glucose utilization in chicken muscles.

Histomorphometric study of the anterior latissimus dorsi muscle and evaluation of enzymatic markers of broilers affected with dorsal cranial myopathy

Dorsal cranial myopathy (DCM), which affects the anterior latissimus dorsi (ALD) muscles of commercial broilers, is of unknown etiology, and it represents up to 6% of the partial condemnations in Brazilian slaughterhouses. This study was performed to achieve histomorphometric characterizations of the ALD muscles from male Cobb 500 broilers slaughtered at either 35 d or 42 d and to evaluate the effects of DCM on the enzymatic markers aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatine kinase (CK), and lactate dehydrogenase (LDH) and on uric acid and creatinine metabolites. Blood samples (1.5 to 3 mL) and ALD muscle fragments were collected from each carcass, all of which were processed in a commercial inline processing system. For each age, twelve macroscopically normal animals and twelve animals found to exhibit DCM were randomly selected for histomorphometric evaluation and analysis of serologic profiles. Microscopic evaluations demonstrated that the muscle fibers of those with DCM exhibited a strong presence of multifocal regenerative myodegeneration as well as a substitution of muscle tissue with connective tissue (P < 0.001) through fibrosis, thus characterizing the chronicity and hardness of the affected muscle. It is suggested that DCM is a localized muscle lesion because the detected serum levels of CK (P < 0.001), AST (P < 0.001), ALT (P = 0.01), and LDH (P < 0.001) enzymes were strongly associated with the group affected by DCM. Additional studies are needed to gain an understanding of this myopathy because it is an emerging problem in the poultry industry. In addition, it is related to DCM lesions in fast-growing broilers with the greatest slaughter weights.

Breast meat quality of chickens with divergent growth rates and its relation to growth curve parameters

Abstract. The effects of the increase of body weight of contemporary broilers during growth on functional meat quality and color characteristics of the chicken breast muscle are controversially debated. Therefore, male chickens (n = 264) of a fast-growing commercial broiler (Ross 308) and two slow-growing experimental meat-type chicken lines were compared at equal age and at similar body weight in order to investigate the effect of growth rate on selected functional breast meat traits and meat color. Additionally, the breast meat characteristics of birds with different growth profiles were compared within lines. When the body weight of commercial broilers reached about 40 to 60 % of their growth potential, they exhibited particularly high ultimate pH values compared with slow-growing lines. The ability of the meat of fast-growing broilers to retain water during cooking was impaired (5 to 16 percentage points increased cooking loss compared to slow-growing lines), which, in contrast to pH, was only marginally affected by body weight and/or age at slaughter. No unfavorable correlations of breast meat quality traits with the growth profile, represented by growth curve parameters derived from the Gompertz–Laird equation, were detected within any of the investigated chicken lines. It is noteworthy that the associations of ultimate pH and cooking loss with maximum growth speed indicate a non-linear relationship. Thus, some of the functional characteristics of breast meat of the fast-growing broiler resembled the white-striping defect described for poultry meat, but the hypothesis that selection on increased growth rates is detrimental for meat quality per se could not be confirmed. In fact, an elevated growth potential in particular, i.e., body weight at maturity, could have some beneficial effects for the water-holding capacity of breast meat, regardless of the genotypic growth rate.

Transcriptional analysis of abdominal fat in chickens divergently selected on bodyweight at two ages reveals novel mechanisms controlling adiposity: validating visceral adipose tissue as a dynamic endocrine and metabolic organ

Background

Decades of intensive genetic selection in the domestic chicken (Gallus gallus domesticus) have enabled the remarkable rapid growth of today’s broiler (meat-type) chickens. However, this enhanced growth rate was accompanied by several unfavorable traits (i.e., increased visceral fatness, leg weakness, and disorders of metabolism and reproduction). The present descriptive analysis of the abdominal fat transcriptome aimed to identify functional genes and biological pathways that likely contribute to an extreme difference in visceral fatness of divergently selected broiler chickens.

Methods

We used the Del-Mar 14 K Chicken Integrated Systems microarray to take time-course snapshots of global gene transcription in abdominal fat of juvenile [1-11 weeks of age (wk)] chickens divergently selected on bodyweight at two ages (8 and 36 wk). Further, a RNA sequencing analysis was completed on the same abdominal fat samples taken from high-growth (HG) and low-growth (LG) cockerels at 7 wk, the age with the greatest divergence in body weight (3.2-fold) and visceral fatness (19.6-fold).

Results

Time-course microarray analysis revealed 312 differentially expressed genes (FDR ≤ 0.05) as the main effect of genotype (HG versus LG), 718 genes in the interaction of age and genotype, and 2918 genes as the main effect of age. The RNA sequencing analysis identified 2410 differentially expressed genes in abdominal fat of HG versus LG chickens at 7 wk. The HG chickens are fatter and over-express numerous genes that support higher rates of visceral adipogenesis and lipogenesis. In abdominal fat of LG chickens, we found higher expression of many genes involved in hemostasis, energy catabolism and endocrine signaling, which likely contribute to their leaner phenotype and slower growth. Many transcription factors and their direct target genes identified in HG and LG chickens could be involved in their divergence in adiposity and growth rate.

Conclusions

The present analyses of the visceral fat transcriptome in chickens divergently selected for a large difference in growth rate and abdominal fatness clearly demonstrate that abdominal fat is a very dynamic metabolic and endocrine organ in the chicken. The HG chickens overexpress many transcription factors and their direct target genes, which should enhance in situ lipogenesis and ultimately adiposity. Our observation of enhanced expression of hemostasis and endocrine-signaling genes in diminished abdominal fat of LG cockerels provides insight into genetic mechanisms involved in divergence of abdominal fatness and somatic growth in avian and perhaps mammalian species, including humans.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-4035-5) contains supplementary material, which is available to authorized users.

Long-term changes in performance and meat quality of Danish Landrace pigs: a study on a current compared with an unimproved genotype

An experiment was conducted in 1995 in order to examine muscle growth, muscle histochemical properties, muscle metabolism and meat quality of two types of Danish Landrace pigs representing the growth potential of years 1976 and 1995, respectively. Danish Landrace pigs representing 1976 (slow-growing, SG) originated from a breeding station where the population was maintained without being selected for production traits such as daily gain, food conversion ratio and meat content. Pigs representing Danish Landrace of 1995 (fast-growing, FG) were bought from certified Danish pig breeders. The pigs were simultaneously tested for performance from 40 to 95 kg live weight. The daily gain, food conversion ratio and meat content of the carcass were improved proportionately by 0·43, 0·24 and 0·03 in FG pigs compared with SG pigs. In m. longissimus dorsi (LD), the cross-sectional area of muscle fibres was smaller in FG pigs compared with SG pigs indicating increased muscle fibre number. Data further suggest increased satellite cell proliferation in muscles of FG pigs. Serum from FG pigs stimulated the proliferation of C2C12 muscle cells to a greater extent than serum from SG pigs, although the serum level of insulin-like growth factor 1 did not differ between pig types. The effect of serum on protein turn-over of C2C12 myotubes did not depend on pig type. The glycogen concentration in the LD did not differ significantly between pig types, while the activity of citrate synthase, 3-OH-acyl-CoA-dehydrogenase, and lactate dehydrogenase were higher in the LD of SG pigs compared with FG pigs. Pork chop colour of FG pigs was proportionately 0·09 lighter (L⋆) and 0·13 less red (a⋆) than pork chops of SG pigs. The total muscle pigment concentration in the LD, m. biceps femoris and m. vastus intermedius was proportionately reduced by 0·17, 0·19 and 0·11, respectively, in FG pigs compared with SG pigs. In the LD, the concentration of myoglobin was proportionately reduced by 0·17 in FG pigs. The chemical composition of the LD differed between pig types such that the water content was higher and protein content lower in LD from FG pigs compared with SG pigs. The pH of the LD measured 45 min and 24 h post mortem, drip loss and thawing loss were similar for both pig types. Meat tenderness of conditioned pork chops of FG pigs was slightly reduced in accordance with a decreased intensity of the 31 kDa peptide band and increased cooking loss. The present study suggests that increased muscle fibre number and rate of muscle DNA deposition (satellite cell proliferation) have contributed to the increased muscle growth as a result of selection for performance in pigs under Danish conditions. However, the increase in growth performance was accompanied by deterioration in muscle colour and slightly reduced tenderness.

Meat quality and the histological structure of breast and leg muscles in Ayam Cemani chickens, Ayam Cemani × Sussex hybrids and slow-growing Hubbard JA 957 chickens

BACKGROUND

The purpose of this study was to determine the quality of meat and the histological structure of muscles of Ayam Cemani chickens, Ayam Cemani × Sussex hybrids and slow-growing Hubbard JA 957 chickens and to examine whether crossing generally available Sussex chickens with little available Ayam Cemani gives a good quality product of interest to the poultry industry and in food technology.

RESULTS

The size of breast and leg muscle fibers varied among genotypes. The breast and leg muscles of slow-growing Hubbard JA 957 chickens had the largest fiber diameter. The histological and biochemical properties of muscles, including the type, number, proportions, diameter and metabolic profile of fibers, had a significant effect on the pH and water-binding capacity of meat, thus affecting its quality. The muscle fibers of Ayam Cemani chickens were approximately half the size of the muscle fibers of Hubbard JA 957 chickens. Ayam Cemani and Ayam Cemani × Sussex gave a product of as good quality as Hubbard JA 957 chickens.

CONCLUSION

Meat from Ayam Cemani chickens is a rich source of protein and could be highly valued by gourmet consumers, connoisseurs and dieticians for its rarity and originality. The results of this study show that genotype (Ayam Cemani, Ayam Cemani × Sussex, Hubbard JA 957) affected the quality and color of meat and the histological profile of chicken breast and leg muscles.

Selecting broiler chickens for ultimate pH of breast muscle: analysis of divergent selection experiment and phenotypic consequences on meat quality, growth, and body composition traits

Genetic parameters for ultimate pH of pectoralis major muscle (PM-pHu) and sartorius muscle (SART-pHu); color parameters L*, a*, b*; logarithm of drip loss (LogDL) of pectoralis major (PM) muscle; breast meat yield (BMY); thigh and drumstick yield (TY); abdominal fat percentage (AFP); and BW at 6 wk (BW6) were estimated in 2 lines of broiler chickens divergently selected for PM-pHu. Effects of selection on all the previous traits and on glycolytic potential, pectoralis major muscle pH at 15 min postmortem, curing-cooking yield (CCY), cooking loss (CL), and Warner-Bratzler shear force (WBSF) of the PM muscle were also analyzed after 5 generations. Strong genetic determinism of PM-pHu was observed, with estimated h(2) of 0.57 ± 0.02. There was a significant positive genetic correlation (rg) between PM-pHu and SART-pHu (0.54 ± 0.04), indicating that selection had a general rather than a specific effect on energy storage in skeletal muscles. The h(2) estimates of L*, a*, and b* parameters were 0.58 ± 0.02, 0.39 ± 0.02, and 0.48 ± 0.02, respectively. Heritability estimates for TY, BMY, and AFP were 0.39 ± 0.04, 0.52 ± 0.01, and 0.71 ± 0.02, respectively. Our results indicated different genetic control of LogDL and L* of the meat between the 2 lines; these traits had a strong rg with PM-pHu in the line selected for low ultimate pH (pHu) value (pHu-; -0.80 and -0.71, respectively), which was not observed in the line selected for high pHu value (pHu+; -0.04 and -0.29, respectively). A significant positive rg (0.21 ± 0.04) was observed between PM-pHu and BMY but not between PM-pHu and BW6, AFP, or TY. Significant phenotypic differences were observed after 5 generations of selection between the 2 lines. The mean differences (P < 0.001) in pHu between the 2 lines were 0.42 and 0.21 pH units in the breast and thigh muscle, respectively. Breast meat in the pHu+ line exhibited lower L* (-5 units; P < 0.001), a* (-0.22 units; P < 0.001), b* (-1.53 units; P < 0.001), and drip loss (-1.6 units; P < 0.001) than in the pHu- line. Breast meat of the pHu+ line was also characterized by greater CCY (+6.1 units; P < 0.001), lower CL (-1.66 units; P < 0.01), and lower WBSF after cooking (-5.1 units; P < 0.001) compared to the pHu- line. This study highlighted that selection based on pHu can be effective in improving the processing ability of breast meat and reducing the incidence of meat quality defects without affecting chicken growth performance.

Anatomical and biomechanical traits of broiler chickens across ontogeny. Part II. Body segment inertial properties and muscle architecture of the pelvic limb

In broiler chickens, genetic success for desired production traits is often shadowed by welfare concerns related to musculoskeletal health. Whilst these concerns are clear, a viable solution is still elusive. Part of the solution lies in knowing how anatomical changes in afflicted body systems that occur across ontogeny influence standing and moving. Here, to demonstrate these changes we quantify the segment inertial properties of the whole body, trunk (legs removed) and the right pelvic limb segments of five broilers at three different age groups across development. We also consider how muscle architecture (mass, fascicle length and other properties related to mechanics) changes for selected muscles of the pelvic limb. All broilers used had no observed lameness, but we document the limb pathologies identified post mortem, since these two factors do not always correlate, as shown here. The most common leg disorders, including bacterial chondronecrosis with osteomyelitis and rotational and angular deformities of the lower limb, were observed in chickens at all developmental stages. Whole limb morphology is not uniform relative to body size, with broilers obtaining large thighs and feet between four and six weeks of age. This implies that the energetic cost of swinging the limbs is markedly increased across this growth period, perhaps contributing to reduced activity levels. Hindlimb bone length does not change during this period, which may be advantageous for increased stability despite the increased energetic costs. Increased pectoral muscle growth appears to move the centre of mass cranio-dorsally in the last two weeks of growth. This has direct consequences for locomotion (potentially greater limb muscle stresses during standing and moving). Our study is the first to measure these changes in the musculoskeletal system across growth in chickens, and reveals how artificially selected changes of the morphology of the pectoral apparatus may cause deficits in locomotion.

Characterization of muscle fiber type in the pectoralis major muscle of slow-growing local and commercial chicken strains

The study aimed to characterize muscle fiber type of the pectoralis major muscle of slow-growing chickens belonging to the Padovana local breed, the commercial strain Berlanda gaina, and their cross. Forty-five chickens (both males and females) from the different genotypes were grown up to 180 d. Histochemical and morphometrical analyses were performed to characterize muscle fiber types, myofiber density, and myofiber size of the different genotypes. The effects of genotype, sex, and their interaction were estimated. Muscle samples appeared almost entirely made up of IIB fiber type, whereas a low percentage of area (5 to 6%) was composed of hypercontracted fiber. Myofiber density was significantly higher (P < 0.05) in Padovana strains and cross-sectional area was significantly lower (P < 0.01) than in Berlanda strain. Muscle fiber characteristics appeared not to be affected by the interaction of genotype × sex.

A mutation in the promoter of the chicken β,β-carotene 15,15'-monooxygenase 1 gene alters xanthophyll metabolism through a selective effect on its mRNA abundance in the breast muscle

A polymorphism in the promoter of the β,β-carotene 15,15'-monooxygenase 1 (BCMO1) gene recently was identified in an experimental cross between 2 chicken lines divergently selected on growth rate and found to be associated with variations in the yellow color of the breast meat. In this study, the effects of the polymorphism on several aspects of carotenoid metabolism were evaluated in chickens sharing the same genetic background except for their genotype at the BCMO1 locus. We confirmed that BCMO1 mRNA abundance varied (P < 0.001) between the 2 homozygous genotypes (GG << AA) and in the pectoralis major muscle. By contrast, BCMO1 mRNA expression was not affected (P > 0.05) by the polymorphism in the duodenum, liver, or sartorius muscle. The breast meat of GG chickens was more (P < 0.001) yellow and richer in lutein (P < 0.01) and zeaxanthin (P < 0.05) compared to that of AA chickens whereas these variables did not differ (P > 0.05) in the other tissues tested. The GG were also characterized by reduced (P < 0.01) plasma lutein and zeaxanthin concentrations than AA without affecting plasma and tissue content of fat-soluble vitamins A and E. As lutein and zeaxanthin are usually not considered as substrates of the BCMO1 enzyme, the impact of BCMO1 polymorphism on the activity of other genes involved in carotenoid transport (SCARB1 and CD36 encoding the scavenger receptor class B type I and the cluster determinant 36, respectively) and metabolism (BCDO2 encoding β,β-carotene 9',10'-dioxygenase 2) was evaluated. The BCMO1 polymorphism did not affect mRNA abundance of BCDO2, SCARB1, or CD36, regardless of tissue considered. Taken together, these results indicated that a genetic variant of BCMO1 specifically changes lutein and zeaxanthin content in the chicken plasma and breast muscle without impairing vitamin A and E metabolism.

Effects of divergent selection for 8-week body weight on postnatal enzyme activity pattern of 3 fiber types in fast muscles of male broilers (Gallus gallus domesticus)

A divergent selection experiment was conducted for 8-wk BW in chickens. At 3, 6, 9, and 12 wk of age, samples of pectoralis profundus (PP) and biceps femoris (BF) muscles from fast-growing and slow-growing lines were used to estimate the enzyme activities and muscle fiber diameter. Microphotometric measurements made in situ of succinate dehydrogenase (SDH, EC 1.3.99.1) and glycerol-3-phosphate dehydrogenase (GPDH, EC 1.1.99.5) were completed on serial sections of PP and BF muscles from male chickens, in order to examine the ratio of SDH:GPDH activity in single fibers. On the basis of the SDH:GPDH activity ratios, muscle fibers were divided using cluster analysis into 3 populations of different fiber types (O = oxidative, OG = oxidative-glycolytic, and G = glycolytic). Cockerels of the SGL attained an 8.1-fold increase and those of the FGL a 6.8-fold increase in BW at 12 wk compared with that at 3 wk of age. The O, OG, and G type fibers of the BF muscles of the SGL had significantly (P ≤ 0.001) lower SDH:GPDH activity ratios than those of the FGL. A step decrease in the SDH:GPDH activity of O, OG, and G fibers in the PP of both lines occurred, and this differed significantly between SGL and FGL (P ≤ 0.001). Age and line effects influenced the diameter of the 3 fiber types in the BF muscle only. In contrast to this response, all 3 fiber types of the PP muscles reached similar diameters in both lines during the growth process from wk 3 to 12. From the results of this study, we concluded that the activities of metabolic enzymes in skeletal muscle fibers are under the influence of muscle type, age, and selection pressure. Microphotometry is a suitable method for the evaluation of enzyme activity measured in a single muscle fiber. The method enables precise estimation of enzyme activities, especially in muscles composed of populations of different metabolic fiber types.

Possible roles of myostatin and PGC-1alpha in the increase of skeletal muscle and transformation of fiber type in cold-exposed chicks: expression of myostatin and PGC-1alpha in chicks exposed to cold

This study examined the hypothesis that myostatin and PGC-1alpha are involved in the increase in skeletal muscle mass and transformation of fiber type in cold-exposed chicks. One-week-old chicks were exposed to acute (24h) or long-term (8d) cold at 4 degrees C or kept warm at 30 degrees C. Acute cold exposure induced a significant increase in the skeletal muscle weight and the ratio of slow- to fast-fiber specific troponin I expression (sTnI/fTnI), accompanied by a significant decrease in lactate dehydrogenase activity. Expression of myostatin mRNA in the muscle was significantly lower in cold-exposed chicks than in the controls, whereas PGC-1alpha mRNA expression was significantly enhanced. These changes in the gene expression rapidly returned to the levels of the control chicks after the end of cold exposure, whereas the changes in fiber type and enzymatic activity were not resumed within 24h after removal of cold exposure. On the other hand, long-term exposure to cold resulted in a remarkable increase in skeletal muscle weight, accompanied by a significant increase in the ratio of sTnI/fTnI and the enzymatic activities of cytochrome oxidase and lactate dehydrogenase. However, the expression level of myostatin mRNA in cold-exposed chicks was not different from that in their age-matched control chicks and that of PGC-1alpha mRNA was significantly lower than in the controls. These results indicate that myostatin and PGC-1alpha expression in the skeletal muscle rapidly change in response to acute cold, suggesting the possibility that these two genes could be involved in the increase in muscle mass and transformation of fiber type, respectively, at the initial stage of adaptation in cold-exposed chicks.

Carcass composition, bone mechanical properties, and meat quality traits in relation to growth rate in rabbits

The objective of this study was to characterize correlated responses in carcass composition, bone mechanical properties, and meat quality indicators to divergent selection for growth rate. Rabbits from low (LOW) or high (HIGH) lines divergently selected over five generations on 63-d BW and a control group (CONT) were used. Rabbits were slaughtered at an average BW of 2,306 +/- 65 g, corresponding to 63, 58, or 52 d of age in LOW (n = 41), CONT (n = 43), and HIGH (n = 44) groups, respectively. Postweaning ADG and G:F increased (P < 0.001) in the order LOW < CONT < HIGH groups. The lengths of the tibia and femur in rabbit legs decreased (P < 0.001) with increasing growth rate. Tibia and femur bone intrinsic stiffness, as assessed by a three-point flexure test, followed the order (P < 0.001) of HIGH < CONT < LOW groups. At the same BW, HIGH rabbits and CONT rabbits showed many similarities for dressing percent, carcass composition, and color and chemical composition of muscles or meat parts. In contrast, carcass yield and the relative proportion of hind part were 3% greater (P < 0.01) in LOW rabbits than in CONT and HIGH rabbits. The meat-to-bone ratio in the hind leg was 11% greater (P < 0.001) in the LOW group compared with the CONT and HIGH groups. Yellow color index and moisture content in LM, a fast-twitch glycolytic muscle, were lower (P < 0.05) in LOW rabbits than in HIGH rabbits, but ultimate pH, WHC, and cooking loss did not differ between the two growth-selected lines. Ultimate pH in semitendinosus, a mixed slow- and fast-twitch oxidoglycolytic muscle, was less (P < 0.001) in HIGH rabbits than in CONT and LOW rabbits. However, lactate dehydrogenase and isocitrate dehydrogenase activities in this muscle (n = 21 per group), assessed at the time of slaughter as markers of glycolytic and oxidative capacities, respectively, did not differ among groups. Growth rate did not modify mean cross-sectional area and type frequency of myofibers in semitendinosus muscle. Finally, Warner-Bratzler shear force and total energy needed to achieve rupture did not differ among groups in semitendinosus muscle (n = 21 per group), whereas they were the least (P < 0.001) in LM (n = 128) from HIGH rabbits. Results from this study indicate that improvement of growth rate by selection has little effect in rabbit carcass and meat quality traits.

Consequence of muscle hypertrophy on characteristics of Pectoralis major muscle and breast meat quality of broiler chickens1

The structural and metabolic characteristics of the pectoralis major (P. major) muscle (i.e., breast muscle) and the quality of the resulting meat were studied in relation to breast muscle fiber development in broiler chickens. Six hundred birds originating from a commercial, grand parental, male heavy line (Hubbard-Europe, Châteaubourg, France) were kept under conventional breeding methods until their usual marketing age of 6 wk. For all birds, the plasma creatine kinase activity and the P. major muscle fiber cross-sectional area (CSA), glycolytic potential, lactate content, pH at 15 min postmortem, as well as the ultimate pH, CIELAB color parameters [lightness (L*), redness (a*), and yellowness (b*)], and drip loss of breast meat, were measured. Increased breast weight and yield were associated with increased fiber CSA, reduced muscle glycolytic potential, and reduced lactate content at 15 min postmortem. Therefore, P. major muscle exhibiting larger fiber CSA exhibited greater pH at 15 min postmortem and ultimate pH, produced breast meat with lower L* and reduced drip loss, and was potentially better adapted to further processing than muscle exhibiting small fiber CSA.

Relationships Among Egg Characteristics, Chick Measurements, and Early Growth Traits in Ten Broiler Breeder Strains

This study evaluated egg traits, yolk utilization, chick conformation, and early growth rate in 10 broiler breeder strains. The strains included pure-, specialized- and commercial-line products. The 210 eggs/strain were weighed and randomly designated to 1 of 3 experimental determinations: 8 eggs for measurement of eggshell conductance, 52 eggs for determination of egg characteristics, and 150 eggs for incubation and chick traits. Egg characteristics included egg weight, specific gravity, yolk weight, albumen weight, albumen height, eggshell weight, and eggshell thickness. Chick traits included navel condition, hock color, chick length, shank length, and abdomen score by manual palpation. At hatch, half the birds per strain were dissected to assess the weight of the yolk sac, heart, liver, and breast muscle. The remaining chicks were randomly distributed into 4 rearing pens for a 14-d assessment of growth rate. There was a 3-g range in egg weight among the strains. Eggs from a pure line had the greatest amount of yolk (22.6 g), with yolk weight ranging to a low of 20.9 g in 2 other strains. The male line strain and 2 female line strains had the highest hatching weights (46.3, 46.5, and 45.4 g, respectively), whereas a commercial strain had the lowest hatching weight (43.1 g). Egg size affected chick weight more than did yolk size. The residual yolk mass at hatch ranged from 5.50 g (in the male line) to 3.70 g in the commercial strains. Residual yolk mass accounted for approximately 10 to 14% of chick BW at hatch. The abdominal palpation score correlated with actual hatch residual yolk weight (r = 0.50; P < 0.0001). At hatch, differences in breast muscle and internal organ weight were present. Shank length at hatch correlated more strongly with 14-d BW (r = 0.39; P < 0.0001) than did hatch weight and 14-d BW (r = 0.35; P < 0.0001). The results of this trial demonstrated significant strain variation in internal organ weight, residual yolk sac mass, and chick carcass reserves, which, when added together, resulted in observable differences in chick weights across strains.

Chicken liver and muscle carnitine palmitoyltransferase 1: nutritional regulation of messengers

In mammals, carnitine palmitoyltransferase 1 (CPT1) is a rate limiting enzyme of fatty acid oxidation. Two isoforms are present. We characterized a full-length cDNA sequence encoding chicken liver L-CPT1 isoform and a partial cDNA sequence encoding chicken muscle M-CPT1 isoform. CPT1 messengers showed the expected tissue specificity. M-CPT1 messenger and CPT1 activity were higher in oxidative than in glycolytic muscle. Expression of both isoforms was assessed in various tissues of genetically fat or lean chickens. Fasting considerably increased L-CPT1 mRNA expression and beta-hydroxyacyl CoA dehydrogenase (HAD) activity in the liver of fat or lean chickens. Unexpectedly, fasting did not increase M-CPT1 mRNA levels nor HAD activity in muscles of either chicken genotype. It however increased succinyl-CoA:3-ketoacid CoA transferase (SCOT) mRNA expression (an enzyme related to ketone body utilization) in oxidative muscle. SCOT messenger was slightly more abundant in oxidative muscle of lean chickens but not in glycolytic muscle. In conclusion, the regulation of fatty acid oxidation is probably not impaired in fat chicken. The absence of fasting stimulation of M-CPT1 mRNA expression, which is at variance with the situation observed in mammals, suggests that during fasting, chicken muscles preferentially use ketone bodies as fuel, at least in the short term.

Comparison of chicken genotypes: myofiber number in pectoralis muscle and myostatin ontogeny

This study was performed to evaluate breast muscle development in chicken genotypes divergently selected for muscularity. In the first experiment, 2 commercial broiler lines (a high breast yield, HBY, and a normal breast yield broiler strain-cross, NBY) and a Leghorn line were grown up to 35 d to evaluate BW, breast weight, and breast yield. At 7 and 21 d of age, pectoralis muscle was used to estimate myofiber density (MFD, number of myofibers per mm2) and total apparent myofiber number (MFN). In the second experiment, the ontogeny of myostatin was determined from broiler- and Leghorn-type chick embryos, at embryonic days 1 to 20 (E1 to E20), using reverse transcription (RT)-PCR. As expected, the Leghorn line had lower BW, breast weight, and breast yield than broiler lines. The HBY line showed higher breast yield at all ages evaluated, but lower BW at 21 and 35 d than the NBY line. The Leghorn line had 45% higher MFD than broilers, which indicates an increased cross-sectional area of the myofibers in broiler lines. No MFD difference was observed between the broiler strains (P > 0.05). The myofiber number of broilers was more than twice that of Leghorns and HBY had 10% higher MFN than the NBY line. Myofiber number was correlated to BW (r = 0.58), breast weight (r = 0.58), and breast yield (r = 0.69). Conversely, MFD showed negative correlation with BW, breast weight, and breast yield (r = -0.85, -0.83, and -0.88, respectively). No effect of genotype or interaction between genotype and embryonic age was observed for myostatin expression. This study showed that broilers have higher MFN in the breast muscles than Leghorn-type chickens, and that high breast yield of broiler strains may be due to increased MFN. Higher muscularity of broilers, as compared with Leghorns, was not attributed to lower expression of myostatin during embryonic development.

Biochemical analyses of muscles from poultry bred for rapid growth

In the current study, commercial broiler breeder hens were mated with either commercial broiler breeder males (B/B) or artificially inseminated with semen from Leghorn cockerels (B/L). Embryos and chicks from each mating were used to study the effects of paternal genotype on breast muscle myosin expression without the confounding effects of differences in egg size and embryo development due to maternal genotype. Specifically, the temporal transitions of myosin heavy chain (MyHC) isoforms within the pectoralis (P.) major and P. minor were measured. The relative concentration of the embryonic MyHC isoform increased from d 17 through 21 in ovo in both genotypes and was higher in B/B embryos than in B/L embryos (P < or = 0.01). At 21 d posthatch, there was an increased proportion of the adult MyHC isoform within the P. major and P. minor in B/B compared with B/L chicks (P < or = 0.01). This result suggests that the B/B chicks were making the transition to mature skeletal muscle more rapidly than the B/L chicks. Although samples taken from the P. minor of B/B and B/ L chicks exhibited an increased proportion of the adult MyHC isoform and lower proportion of the neonatal MyHC isoform at 21 d, the genetic differences were far more pronounced in the larger P. major (P < or = 0.01). In summary, the P. major from the faster growing B/B chicks exhibited earlier temporal transitions of developmental fast MyHC, and these differences were evident as early as 17 d in ovo.

Breast muscle development in commercial broiler chickens

Genetic and gender-related variations in breast muscle yield of broiler chickens may be attributed to differences in number and size of muscle cells (myofibers). In this study, male and female broilers from eight commercial strain crosses (SC) were compared for body and breast muscle weight with adjustment of the Gompertz function. Additionally, breast fillet dimensions (length, width, and depth) and myofiber density (myofiber number/area; MFD) were assessed. Live weight and breast muscle development was determined to 56 d of age at weekly intervals. MFD was assessed at 8 d of age. As expected, SC differed in BW, breast weight and yield, and breast fillet dimensions and had variations in growth curves. Maximal growth rate for breast weight was reached approximately 4 d after that of BW. Males and females showed different growth curves, with males having slower growth rate maturity parameter and reaching the maximal growth rate later than females for BW and breast weight. Breast depth was the breast measure with highest positive correlation to breast yield. SC differences could not be explained by MFD, but males had higher MFD density than females. The possible relationship of the MFD observations to total myofiber number is discussed.

Systems-wide chicken DNA microarrays, gene expression profiling, and discovery of functional genes

The goal of our current consortium project is to launch a new era--functional genomics of poultry--by providing genomic resources [expressed sequence tags (EST) and DNA microarrays] and by examining global gene expression in target tissues of chickens. DNA microarray analysis has been a fruitful strategy for the identification of functional genes in several model organisms (i.e., human, rodents, fruit fly, etc.). We have constructed and normalized five tissue-specific or multiple-tissue chicken cDNA libraries [liver, fat, breast, and leg muscle/epiphyseal growth plate, pituitary/hypothalamus/pineal, and reproductive tract (oviduct/ovary/testes)] for high-throughput DNA sequencing of EST. DNA sequence clustering was used to build contigs of overlapping sequence and to identify unique, non-redundant EST clones (unigenes), which permitted printing of systems-wide chicken DNA microarrays. One of the most promising genetic resources for gene exploration and functional gene mapping is provided by two sets of experimental lines of broiler-type chickens developed at INRA, France, by divergent selection for extremes in growth traits (fast-growing versus slow-growing; fatness versus leanness at a similar growth rate). We are using DNA microarrays for global gene expression profiling to identify candidate genes and to map growth, metabolic, and regulatory pathways that control important production traits. Candidate genes will be used for functional gene mapping and QTL analysis of F2 progeny from intercrosses made between divergent genetic lines (fat x lean lines; fast-growing x slow-growing lines). Using our first chicken liver microarray, we have already identified several interesting differentially expressed genes in commercial broilers and in divergently selected broiler lines. Many of these candidate genes are involved in the lipogenic pathway and are controlled in part by the thyrotropic axis. Thus, genome-wide transcriptional profiling is a powerful tool used to visualize the cascade of genetic circuits that govern complex biological responses. Global gene expression profiling and QTL scans should enable us to functionally map the genetic pathways that control growth, development, and metabolism of chickens. This emerging technology will have broad applications for poultry breeding programs (i.e., use of molecular markers) and for future production systems (i.e., the health and welfare of birds and the quality of poultry products).

Effects of delayed feed intake on body, intestine, and muscle development in neonate broilers

The short-term effects of delayed feeding (DF) for 2 d posthatching were measured in neonate chicks and compared to early feeding (EF). Chicks from 10 independent families were used in this study to determine whether genetic background control of growth may be influenced by EF and DF. Early feeding maintained significant interfamily body weight variations from hatch to 4 d of age, whereas there were no significant differences from 1 d of age when feeding was delayed to 48 h posthatching. These results suggest that posthatching feeding delay may distort genetic selection by masking the expression of genetic potential and disturbing the estimation of chick breeder value. In DF chicks, overall body growth was delayed until the beginning of feeding and body weight at 6 d of age was 25% lower than EF chicks. Availability of feed after the fasting period was not sufficient to compensate for the retardation of weight gain in either body weight or in intestine and breast muscle weight. However, initiation of intestine growth in DF chicks occurred from 1 d of age despite the lack of feeding, whereas feed intake was essential to enhance muscle growth. The potential for protein synthesis was lower in DF than in EF chicks during the first 2 d posthatching (P < 0.001) and then reached similar values after feed intake. These results confirm that initiation of growth in neonate chicks is improved by earlier feeding after hatching. Awareness of changes in overall body weight caused by posthatching food deprivation, especially in the intestine and muscle might help in the development of new diets which could minimize retardation of body weight gain in chicks.

Muscle development, insulin-like growth factor-I and myostatin mRNA levels in chickens selected for increased breast muscle yield

Insulin-like growth factor-I (IGF-I) and myostatin (MSTN) are paracrine regulators of muscle growth. The present study was conducted to relate their expression with muscle fibre development in chickens selected for high breast meat yield and their controls. Both mRNA levels were measured by real-time RT-PCR in the Pectoralis major (PM) muscle between 14 days in ovo and 6 weeks post-hatch and in the Sartorius (SART) muscle between 2 and 6 weeks. The data show that PM growth was slow during in ovo development and rapid in the early post-hatch period. Chickens from the selected genotype exhibited significantly higher breast muscle yields from 2 to 6 weeks of age, and muscle fibre hypertrophy. In the PM, IGF-I and MSTN mRNA levels decreased markedly around hatch, while the IGF-I/MSTN ratio increased, suggesting that it could contribute to the explosive growth observed in the early post-hatch period. Between 4 and 6 weeks of age in selected chickens, IGF-I mRNA levels were significantly higher (p=0.04) with a similar trend in MSTN mRNA levels (p=0.07) in the PM muscle but not in the SART muscle. Our results support the hypothesis that the relative levels of IGF-I and MSTN mRNA may participate to set muscle growth rate along development, while other factors are required to explain differences between genotypes.

Effect of selection for improved body weight and composition on muscle and meat characteristics in Muscovy duck

1. For 25 years, the Muscovy duck has been selected for greater body weight at slaughter age, higher meat yield and lower fat content. The aim of this study was to analyse the effects of such selection on the biochemical and technological characteristics of duck meat. 2. A line which has been maintained without any selection since 1975 (control line) and a heavy line now commercialised (selected line) were reared under the same conditions. We compared growth performances, dressing and dissection yields and biochemical and technological characteristics of duck meat at 8, 10 and 12 weeks of age. 3. Our results showed that an indirect effect of selection was to increase the duck growth rate. At a given age, muscle weights and yields as well as carcase fat content were higher for selected ducks. In the selected line, muscle fibres were larger and the collagen content in muscles lower. 4. The Sartorius muscle in ducks from the selected line exhibited a higher percentage in numbers of white type IIb fibres to the detriment of red type IIa fibres. Its glycolytic enzyme activity was higher and its oxidative enzyme activity lower. 5. In breast muscle, selection decreased the rate of post-mortem decline in pH value, increased protein and mineral contents and decreased moisture. It did not affect fibre type, colour, haem pigment and lipid contents, collagen solubility or drip loss. 6. In conclusion, the effects of Muscovy duck selection on meat quality were relatively moderate.

Muscle protein turnover during early development in chickens divergently selected for growth rate

To explore the mechanisms involved in the genetic control of muscle growth and protein gain, protein metabolism was assessed in the pectoralis major muscle of two chicken lines selected for either fast or slow growth. Protein synthesis was measured in vivo at various ages from 1 to 4 wk, using a flooding dose of L-[4-3H] phenylalanine. Protein degradation was estimated as the difference between synthesis and deposition. Over the experimental period, BW were about 2-fold greater (P < 0.001), and pectoralis major muscle weights were 2.4- to 3.6-fold higher (P < 0.001), in chicks from the fast-growing line (FGL) than those from the slow-growing line (SGL). Independent of age, absolute rates of protein deposition, synthesis, and breakdown were higher in FGL than in SGL chickens. Fractional rates of muscle protein synthesis clearly decreased with age. When comparing birds of the same age, fractional rates of muscle protein synthesis tended to be lower in the FGL. Fractional degradation rates (KD) were significantly lower in FGL chickens during the first 2 wk of post-natal growth, whereas KD were similar between lines in older chickens. In this experimental model of chicken lines divergently selected for BW, the greatest line-related difference in muscle protein metabolism was in KD, and was observed in the early growth phases.

Muscle growth in wild and domestic ducks

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

Effect of sex on growth, technological and organoleptic characteristics of the Muscovy duck breast muscle

1. The aim of our study was to analyse the consequences of sexual dimorphism on muscular growth and on technological and organoleptic characteristics of breast muscle. Ten males and 10 females of the R51 line (Grimaud) were weighed every fortnight, from 1-d-old to 15 weeks of age, and then slaughtered. Four muscles, Sartorius (SART), Anterior and Posterior latissimus dorsi (ALD, PLD), Pectoralis major (PM) were removed and weighed. The activities of 3 enzymes (citrate synthase, beta-hydroxyacyl CoA dehydrogenase, lactate dehydrogenase) which indicate muscular metabolic activity were assayed. pH value, colour and juice loss of breast muscle were measured on ducks slaughtered between 8 and 15 weeks of age. Sensory analysis, (tastes) was also carried out. 2. At 15 weeks of age, males weighed 4573 g and females 2879 g. Muscle weight and muscular glycolytic activity increased regularly with age. Females showed earlier muscular growth. Sexual dimorphism had a significant effect on muscular growth from 6 weeks of age for ALD, 8 weeks of age for PLD and SART and 10 weeks of age for PM. 3. With age, breasts became redder and darker. The post-mortem fall of pH and juice loss after 24 h of storage at 4 degrees C increased. Females displayed more precocious muscular maturity. The changes in organoleptic characteristics showed a decrease in tenderness, juiciness and mellowness and an increase in flavour and stringiness with age. At any given age, female breast muscles appeared less tender, less juicy and less mellow but had a more intense flavour and seemed more stringy than those of males.

Muscle insulin-like growth factor-I (IGF-I) receptors in chickens with high or low body weight: effects of age and muscle fibre type

IGF-I receptors were characterized in leg and breast muscles from 1- and 7-week-old chickens selected for high (HG) or low (LG) growth rate. Following whole muscle solubilization, receptors were partially purified by wheat germ agglutinin (WGA) chromatography. IGF-I and insulin binding did not differ between genotypes, but significantly decreased with age, without any change in receptor affinity. In the older birds, insulin binding was lower in breast than in leg muscle, whereas IGF-I binding was similar. Using the artificial substrate poly(Glu-Tyr) 4:1, the IGF-I-stimulated tyrosine kinase activity of the receptors was measured and compared between genotypes (at 1 week), and in HG chickens between muscle types (1 and 7 weeks) and ages (in leg muscle). It was not modified by any of these factors. We conclude that: (1) IGF-I and insulin receptor number do not differ between genotypes, (2) the number of both receptors decreases with age, and (3) in 7-week-old birds, breast muscle could become less responsive to insulin than leg muscles, following a decrease in receptor number.

Comparative analysis of satellite cell properties in heavy- and lightweight strains of turkey

The growth of muscle during postnatal development results partly from the proliferation of satellite cells and their fusion with muscle fibres. We analysed the properties of satellite cells in a heavyweight (HW) turkey strain characterized by high body weight and a fast growth rate, and in a lightweight farm strain (LW) characterized by low body weight and a slow growth rate. Satellite cell activation was then examined in stretched-overloaded anterior latissimus dorsi (ALD) muscle by weighting one wing in young turkeys from both strains. As early as day 1 of stretching for HW and day 2 for LW, small embryonic-like fibres expressing ventricular cardiac myosin heavy chain (MHC) isoform were observed. Following four days of stretching, the number of nascent fibres had increased in both strains but was significantly greater in HW than LW ALD muscle. The proliferation and differentiation capacities of satellite cells from HW and LW strains were investigated in culture. As judged by in vitro measurements of 3H-thymidine incorporation and DNA content, satellite cells of HW turkey exhibited a greater proliferative capability than those of LW turkey. No differences in the temporal appearance of muscle markers (desmin, MHC isoforms) were noted in vitro between the two strains. These data confirm our in vivo observations indicating that selection based on growth rate does not modify muscle fibre maturation. Our in vivo and in vitro observations suggest that variations in the postnatal muscle growth pattern between HW and LW strains may be related to a difference in the capacity of their satellite cells to proliferate.

Posthatching myofiber development in the M. pectoralis of White Pekin Ducks

BACKGROUND

A posthatching transformation of fast-twitch oxidative-glycolytic (FTO) to fast-twitch glycolytic (FTG) fibers in the breast muscle in domestic chickens and turkeys is well documented. There is, however, no information on the situation in Anseriformes having a M. pectoralis with a mixed fiber composition in adults. Differences in the growth of the different fiber types were reported for some muscles in ducks as well as in other birds. They are examined in the main flight muscle using growth curve analysis, until now mostly applied to the analysis of overall growth.

METHODS

Biopsies were taken longitudinally from the M. pectoralis, Pars thoracica, of 40 White Pekin Ducks at 11 different ages from hatching through day 146. The samples were processed for a combination of nicotinamide adenine dinucleotide tetrazolium reductase and myosin adenosine triphosphatase after acid preincubation at pH 4.1. Mean fiber diameter was determined for the different fiber types in relation to age. The Janoschek growth curve was fitted to these values.

RESULTS

FTG fibers were first detected at 20 days of age. Thereafter, the fiber composition hardly changed. When distinguishable by enzyme histochemistry, FTG fibers were already larger in diameter than FTO. There were only gradual differences in the growth pattern. FTG fibers, however, showed much higher absolute, percentage, and relative growth rates. The radial growth of myofibers is slow when compared to other one-dimensional measurements.

CONCLUSIONS

Fiber transformation seems to take place within a short age period. However, further studies are necessary to discriminate effects resulting from sample depth. FTG fibers are presumably recruited from those FTO fibers that show higher growth rates. Growth curve analysis, more frequently used in gross morphological studies, provides an analytical tool for evaluating growth processes of cells and tissues as well. Fiber size differences are mainly due to a higher growth rate in FTG fibers, whereas the growth patterns show only minor differences.

Relative responses of protein turnover in three different skeletal muscles to dietary lysine deficiency in chicks

1. The effect of lysine deficiency was analysed on muscle protein turnover in 2-, 3- and 4-week-old growing broilers. Protein fractional synthesis rates (FSR, in %/d) were measured by a reliable in vivo technique (flooding dose of L-[4-3H] phenylalanine) in the Pectoralis major (PM), the Anterior latissimus dorsi (ALD) and the Sartorius (SART) muscles. Protein fractional breakdown rates (FBR, in %/d) were estimated as the difference between the synthesis rates and the growth rates of tissue protein. 2. Lysine deficiency resulted in significant increases in muscle FSR and FBR. When expressed in absolute rates (g/d), tissue protein deposition was reduced whatever the tissue. This phenomenon was accompanied by decreased protein synthesis (ASR). 3. The protein turnover responsiveness to the lysine deficiency appeared to depend on the studied muscle, since the PM muscle was the most sensitive whereas the SART and ALD muscles presented a lower sensitivity.

Age-related changes of protein turnover in specific tissues of the chick

The effect of age on muscle and liver protein turnover was analyzed in growing broilers. Protein turnover was compared in the Pectoralis major (PM), the Anterior Latissimus dorsi (ALD), and the Sartorius (SART) muscles, as well as in the liver in broilers at three ages (2, 3, and 4 wk). Protein fractional synthesis rates (FSR, in percentage per day) were measured by a flooding dose of L-[4-3H] Phe. Protein fractional breakdown rates (FBR, in percentage per day) were estimated as the difference between FSR and the gain rates of tissue protein. When expressed in absolute rates (grams per day), tissue protein deposition increased during chick growth (approximately 1.7-fold, whatever the tissue). This phenomenon was accompanied by increased protein synthesis (ASR) and proteolysis (ABR) in the PM and in the ALD muscles as well as in the liver. However, ASR and ABR did not seem to be significantly modified in SART. The FSR in skeletal muscles significantly decreased with age. This developmental decline was associated with decreases in RNA content and RNA: protein ratio (Cs, capacity for protein synthesis). In contrast to muscle, we found no significant variation in liver FSR between 2 and 4 wk of age. In addition, liver Cs and translational efficiencies were not decreased. Finally, in muscle as in liver, FBR did not show any clear age-related pattern.