Genetic models for the study of insulin-like growth factors (IGF) and muscle development in birds compared to mammals

Haplotype structure of MSTN, IGF1, and BMP2 genes in Tunisian goats (Capra hircus) and their association with morphometric traits

The aim of the present study was to evaluate variability and haplotype structure of twenty-eight single nucleotide polymorphisms (SNPs) at myostatin (MSTN), insulin-like growth factor 1 (IGF1), and bone morphogenetic protein 2 (BMP2) genes. Association between the polymorphic SNPs and morphometric traits was performed on a population of 263 Tunisian goats. The SNPs analyzed were all polymorphic (except one), and the three genes had different haplotype structures. Significant association of SNPs at MSTN with head length was highlighted in the Tunisian goats. The variability at IGF1 gene was associated with body length, ear length, tail length, and chest depth. For BMP2, significant association was revealed with chest depth. Significant association was also detected between linkage disequilibrium (LD) block 2 at IGF1 with body length. These findings might play a potential role in gene-assisted programs.

Skeletal muscle and metabolic flexibility in response to changing energy demands in wild birds

Phenotypically plastic responses of animals to adjust to environmental variation are pervasive. Reversible plasticity (i.e., phenotypic flexibility), where adult phenotypes can be reversibly altered according to prevailing environmental conditions, allow for better matching of phenotypes to the environment and can generate fitness benefits but may also be associated with costs that trade-off with capacity for flexibility. Here, we review the literature on avian metabolic and muscle plasticity in response to season, temperature, migration and experimental manipulation of flight costs, and employ an integrative approach to explore the phenotypic flexibility of metabolic rates and skeletal muscle in wild birds. Basal (minimum maintenance metabolic rate) and summit (maximum cold-induced metabolic rate) metabolic rates are flexible traits in birds, typically increasing with increasing energy demands. Because skeletal muscles are important for energy use at the organismal level, especially to maximum rates of energy use during exercise or shivering thermogenesis, we consider flexibility of skeletal muscle at the tissue and ultrastructural levels in response to variations in the thermal environment and in workloads due to flight exercise. We also examine two major muscle remodeling regulatory pathways: myostatin and insulin-like growth factor -1 (IGF-1). Changes in myostatin and IGF-1 pathways are sometimes, but not always, regulated in a manner consistent with metabolic rate and muscle mass flexibility in response to changing energy demands in wild birds, but few studies have examined such variation so additional study is needed to fully understand roles for these pathways in regulating metabolic flexibility in birds. Muscle ultrastrutural variation in terms of muscle fiber diameter and associated myonuclear domain (MND) in birds is plastic and highly responsive to thermal variation and increases in workload, however, only a few studies have examined ultrastructural flexibility in avian muscle. Additionally, the relationship between myostatin, IGF-1, and satellite cell (SC) proliferation as it relates to avian muscle flexibility has not been addressed in birds and represents a promising avenue for future study.

Synergistic Effects Between Dietary Zinc Form Supplementation and Dietary Protein Levels on Performance, Intestinal Functional Topography, Hemato-biochemical Indices, Immune, Oxidative Response, and Associated Gene Expression of Nile Tilapia Oreochromis niloticus

The present study investigates the effect of different dietary protein levels suboptimum level (25%) and optimum level (35%), different Zn forms bulk zinc oxide (BZnO) or nanoparticles zinc oxide (NZnO), and their interaction on performance, intestinal topography, hematology, serum biochemical, antioxidant-immune responses, and related gene expression of Nile tilapia. Six experimental diets were formulated to contain approximately 25% and 35% crude protein and supplemented with Zn forms with 0 (normal level in ingredients), 60 mg kg^-1 BZnO and 60 mg kg^-1 nanoparticles of NZnO. Nile tilapia, Oreochromis niloticus, fingerlings (7.53 ± 0. 06 g) were fed on one of tested diets in triplicates with 5% of total biomass three times a day for 84 days. Results showed that, fish fed diet containing 35% crude protein and supplemented with NZnO form recorded the highest final body weight (FBW), weight gain (WG), and specific growth rate (SGR). However, no significant (P > 0.05) differences were recorded in FBW, WG, SGR, feed conversion ratio (FCR), and protein efficiency ratio (PER) between fish fed diet containing 35% crude protein without Zn supplementation and fish fed diet containing 25% crude protein supplemented with NZnO form. Either fish fed diet containing 25% or 35% crude protein and supplemented with NZnO exhibited the highest values of villi height/width. The highest absorption surface area (ASA) was obtained in fish fed diet containing 25% or 35% crude protein and supplemented with BZnO. Hemoglobin (Hb), hematocrit (Hct), and red blood cell count (RBCs) highest values were obtained for fish fed diet containing protein level 35% supplemented with NZnO. Fish fed diet containing protein level 35% and supplemented with NZnO had the lowest value of alanine amino transferase (ALT) and aspartate amino transferase (AST). The highest globulin value was recorded for fish provided with diet containing 35% crude protein and supplemented with BZnO followed by those fed diet containing 35% crude protein and supplemented with NZnO. Fish fed diet containing protein level 25% with NZnO supplementation recorded the highest super oxide dismutase (SOD), catalase (CAT), glutathione reductase (GSH), and glutathione peroxidase (GP_X), with decreasing malondialdehyde (MAD) values. The highest values of immunoglobulin g (IgG), immunoglobulin M (IgM), complement 4 (C4), and complement 3 (C3) were obtained for diet containing 35% crude protein and supplemented with NZnO form. Growth hormone gene (GH) was upregulated in fish fed 25% dietary protein without Zn supplementation, while it was downregulated in fish fed 25% dietary protein and supplemented with NZnO. Transcription of insulin-like growth factor-1 (IGF-I) gene recorded the highest value for fish fed 35% crude protein and supplemented with BZnO. This is although the diet of 35% crude protein + NZnO induced significant (IGF-I) gene expression compared with 25% crude protein with or without BZnO. Therefore, nano zinc is useful as a feed supplement for Nile tilapia (Oreochromis niloticus).

The Effect of Commercial Genetic Selection on Somatotropic Gene Expression in Broilers: A Potential Role for Insulin-Like Growth Factor Binding Proteins in Regulating Broiler Growth and Body Composition

The somatotropic axis influences growth and metabolism, and many of its effects are a result of insulin-like growth factor (IGF) signaling modulated by IGF-binding proteins (IGFBPs). Modern commercial meat-type (broiler) chickens exhibit rapid and efficient growth and muscle accretion resulting from decades of commercial genetic selection, and it is not known how alterations in the IGF system has contributed to these improvements. To determine the effect of commercial genetic selection on somatotropic axis activity, two experiments were conducted comparing legacy Athens Canadian Random Bred and modern Ross 308 male broiler lines, one between embryonic days 10 and 18 and the second between post-hatch days 10 and 40. Gene expression was evaluated in liver and breast muscle (pectoralis major) and circulating hormone concentrations were measured post-hatch. During embryogenesis, no differences in IGF expression were found that corresponded with difference in body weight between the lines beginning on embryonic day 14. While hepatic IGF expression and circulating IGF did not differ between the lines post-hatch, expression of both IGF1 and IGF2 mRNA was greater in breast muscle of modern broilers. Differential expression of select IGFBPs suggests their action is dependent on developmental stage and site of production. Hepatic IGFBP1 appears to promote embryonic growth but inhibit post-hatch growth at select ages. Results suggest that local IGFBP4 may prevent breast muscle growth during embryogenesis but promote it after hatch. Post-hatch, IGFBP2 produced in liver appears to inhibit body growth, but IGFBP2 produced locally in breast muscle facilitates development of this tissue. The opposite appears true for IGFBP3, which seems to promote overall body growth when produced in liver and restrict breast muscle growth when produced locally. Results presented here suggest that paracrine IGF signaling in breast muscle may contribute to overall growth and muscle accretion in chickens, and that this activity is regulated in developmentally distinct and tissue-specific contexts through combinatorial action of IGFBPs.

Central administration of insulin-like growth factor-2 suppresses food intake in chicks

Insulin-like growth factor (IGF)-2 is a multifunctional hormone with structural and functional similarity to IGF-1 in mammals and chickens. We previously showed that intracerebroventricular administration of IGF-1 suppresses food intake in chicks. Also, central administration of IGF-2 suppresses food intake in rats. In the present study, we evaluated whether IGF-2 is involved in the regulation of food intake in chicks. We also examined the effects of fasting on the mRNA levels of IGF binding proteins (IGFBPs) in the liver and hypothalamus, because IGFBPs bind IGF-1 and -2 in plasma and block their binding to the receptors, and locally expressed IGFBPs also influence IGFs binding to the receptors in mammals. Intracerebroventricular administration of IGF-2 significantly suppressed food intake in chicks. The mRNA levels of IGFBPs in the hypothalamus were not affected by six hours of fasting. On the other hand, six hours of fasting markedly increased the mRNA levels of hepatic IGFBP-1 and -2 (5.47- and 6.95-fold, respectively). The mRNA levels of IGFBP-3 were also significantly increased (1.36-fold) by six hours of fasting, whereas the mRNA levels of IGF-2, IGFBP-4, and -5 were unchanged. These findings suggest that circulating IGF-2 may be involved in satiety signals, but its physiological role may be regulated by IGFBPs production in the liver in chicks.

Tryptophan in poultry nutrition: Impacts and mechanisms of action

Many studies have shown that productivity, immune system, antioxidant status, and meat and egg quality can be optimized by dietary supplementation with amino acids that are not usually added to poultry diets. Understanding the effects of these amino acids may encourage feed manufacturers and poultry producers to include them as additives. One of these amino acids is tryptophan (Trp). The importance of Trp is directly related to its role in protein anabolism and indirectly related to its metabolites such as serotonin and melatonin. Thus, Trp could affect the secretion of hormones, development of immune organs, meat and egg production, and meat and egg quality in poultry raised under controlled or stressed conditions. Therefore, this review discusses the main roles of Trp in poultry production and its mode (s) of action in order to help poultry producers decide whether they need to add Trp to poultry diets. Further areas of research are also identified to address information gaps.

Effect of embryonic and post-hatch photo-stimulation with variable light sources on hatchability, endocrine parameters and growth performance in broiler chicken

The objective of this study was to investigate the effects of embryonic and post-hatch photo-stimulation with variable light sources with respect to hatchability parameters, hormonal profile and growth performance of commercial broiler chicken. Uniform sized Cobb broiler eggs (174) were procured from commercial hatchery and incubated in three different groups with arrangement of variable colour light source [Control group; Red light photo-stimulated (675 nm); Green light photo-stimulated group (575 nm) of light]. After hatching, as per earlier grouping, chicks hatched out from respective groups reared under continuous lighting in normal, red, green light up to six week of age in standard management condition in battery cages. The result of the present study indicated that photo-stimulation of incubated eggs with different lights sources had no significant effect on hatchability percentage and hatching time. Green light photo-stimulated group showed significantly higher body weight gain with better feed conversion ratio than red and control groups from 0 to 6 wk of age. Feed intake did not differ significantly within the groups. Green light photo-stimulation promotes growth performance traits via stimulating circulating level of gonadal axis and somatotrophic axis hormone. The results of the study provide evidence that green light photo-stimulation used in this study is beneficial in terms of improved growth performance without affecting hatchability in broiler chicken.

Thermal stress consequences on growth performance, immunological response, antioxidant status, and profitability of finishing broilers: transcriptomic profile change of stress-related genes

The current study was conducted to investigate the impact of thermal stress on growth performance, blood biomarkers, metabolic hormones, immunological response, antioxidant activity, and expression of stress-related genes in broilers. One hundred and fifty one-day-old chicks (Ross 308) were utilized in this work. On the 21st day of age, birds were subjected to three environmentally controlled treatments with five replicate pens of 10 birds per each, representing an initial density of 10 birds/m²-control: reared in a thermoneutral condition; THS₁ and THS_2: exposed to 4 and 6 h of daily thermal stress at 40 ± 1 °C, respectively, until the 42 days of age. The results demonstrated that thermal stress for 4 and 6 h significantly reduced (P < 0.001) daily weight gain, daily feed intake, blood leukocyte and lymphocyte counts, serum immunoglobulins (IgM, IgA, IgG), and insulin-like growth factor-1 (IGF-1), while serum levels of aspartate aminotransferase, alanine aminotransferase, glucose, cholesterol, low-density lipoprotein, and lactate dehydrogenase were elevated relative to the thermoneutral group. Additionally, the corticosterone level and the ratio of heterophil:lymphocyte increased significantly (P < 0.001) in thermal-stressed groups. The antioxidant enzymes were affected by thermal stress as represented by a significant decrease in the activity of serum catalase (CAT) and glutathione peroxidase (GSH-Px) along with an increase in malonaldehyde concentration. Thermal stress affected gene expression by upregulating heat shock protein 70, heat shock factors 1 and 3, nuclear factor kappa B, interleukin-4, and uncoupling protein, and downregulating GSH-Px, CAT, and IGF-1 transcript levels. However, no changes were observed in interleukin-2 expression levels. It can be concluded that thermal stress destructively influences productivity, physiological status, and gene expression by upregulating heat shock protein 70, heat shock factors 1 and 3, nuclear factor kappa B, interleukin-4, and uncoupling protein, and downregulating GSH-Px, CAT, and IGF-1 transcript levels of broiler chickens.

Dietary supplementation with avilamycin and Lactobacillus acidophilus effects growth performance and the expression of growth-related genes in broilers

Context The use of antibiotics in poultry production is appropriate; however, it brings a high risk of dissemination of antibiotic-resistant strains of pathogenic and non-pathogenic bacteria and their further transmission to humans via the food chain. Aims The effects of supplementation with Lactobacillus acidophilus (a probiotic) or avilamycin (an in-feed antibiotic growth promoter), on growth performance, digestibility, plasma lipid levels, and the expression of certain growth-related genes were investigated. Methods In total, 135 15-day-old broiler chicks were divided into three groups (n = 45): a control group and two treatment groups. Each treatment group was then further divided into three replicates (15 birds each). The control group was fed a basal diet; the second group received basal diet supplemented with avilamycin (0.1 g/kg); the third group received basal diet plus L. acidophilus (0.1 g/kg). Growth performance (bodyweight, feed intake and feed-conversion ratio) was measured. Digestibility and gene expression were measured at the end of the experiment. Key results Greatest bodyweight gain was achieved in the L. acidophilus-fed chicks, which were significantly (P &lt; 0.05) heavier than the control chicks and the avilamycin-fed chicks. Addition of avilamycin or L. acidophilus to the diet also significantly improved feed efficiency (P &lt; 0.05) compared with the control. Although the digestibility of dry matter, crude protein and crude fibre significantly improved in the two experimental groups compared with the control, ether extract was not affected. In addition, plasma total cholesterol, triglyceride and low-density-lipoprotein cholesterol levels were significantly (P &lt; 0.05) decreased whereas plasma high-density-lipoprotein cholesterol was significantly (P &lt; 0.05) increased in the L. acidophilus group compared with the control. Expression of the genes for growth hormone secretagogue receptor (GHSR), insulin-like growth factor 1 (IGF-1) and insulin-like growth factor 1 receptor (IGF1R) was remarkably upregulated in the skeletal muscles of the two experimental groups. Conclusions Supplementation with L. acidophilus (0.1 g/kg) in the broiler diet had positive effects on growth, feed intake, feed efficiency, digestibility, and plasma lipid levels of the broilers. Implications Lactobacillus acidophilus might be a more useful additive in broiler feed than antibiotic growth promoters such as avilamycin.

Gene Effects on Body Weight, Carcass Yield, and Meat Quality of Thai Indigenous Chicken

The selection of rapidly growing animals in breeding programs has had inadvertent detrimental effects on meat quality. Thus, the aim of the present study was to investigate the relationship between body weight (BW) and meat quality traits, and the effects of genes encoding insulin-like growth factor I (IGF-I), insulin-like growth factor II (IGF-II), melanocortin-4 receptor (MC4R), and calpain 1 (CAPN1) on BW, carcass yield, and meat quality of the Thai indigenous chicken, Leung Hang Khao. Five hundred and ten chickens were used for genotyping. PCR-restriction fragment length polymorphism and PCR-single strand conformation polymorphism were used to determine the genotypes of IGF-I, IGF-II, MC4R, and CAPN1. BWs were collected from 0–16 weeks of age. The chickens were sacrificed at 16 weeks and individual carcass yields and meat qualities (drip loss, cooking loss, and shear force) were recorded. The correlations between BW and meat qualities were determined. Significant correlation between BW and cooking loss and shear force of breast meat and between BW and drip loss of thigh meat were detected (P<0.05); however, the magnitude of the association was low (−0.1–0.1). IGF-I was eliminated from the association analysis because genotype AA was lost and the frequency of occurrence of the AC genotype was low (0.04). Significant associations between IGF-II, CAPN1, and BW, and CAPN1 and meat quality were detected, while non-significant association between MC4R and BW was observed. The results indicated a low, negative relationship between BW and meat quality, and that the IGF-II and CAPN1 could be used as genetic markers in Leung Hang Khao chickens to improve growth and meat quality through breeding.

Effect of the <i>IGF-I</i> gene polymorphism on growth, body size, carcass and meat quality traits in Coloured Polish Merino sheep

Abstract. Insulin-like growth factor I, encoded by the IGF-I gene, plays a role in cell growth and differentiation, embryogenesis, metabolism regulation, skeletal growth, and protein synthesis. The aims of this study were to investigate the polymorphism in the 5′ flanking region of the IGF-I gene and evaluate associations between the single-nucleotide polymorphism (SNP) in this gene and growth, body size, carcass and meat quality traits in Coloured Polish Merino sheep. In total 78 live and post mortem traits were investigated. Polymorphism in the IGF-I gene was identified with the use of the polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) method in 305 Coloured Polish Merino sheep. In association studies, traits of interest were analysed with the use of the MIXED and GENMOD procedures of the SAS statistical package. Two alleles named A and B, and two IGF-I genotypes – AA and AB – were detected. The A allele and the AA genotype were predominant, with the frequencies of 91.6 and 83.3 %, respectively. The IGF-I genotype was found to have a highly significant effect on fore shank weight (P  =  0.006), kidney fat class (P  =  0.002) and EUROP fat class (P  =  0.005). Furthermore, the IGF-I genotype significantly affected external fatness of carcass class (P  =  0.038), drip loss (P  =  0.049), and subjective assessment of meat colour (P  =  0.043), and it tended to be associated with longissimus dorsi (LD) muscle width (P  =  0.063) and flavour (0.067). Concluding, the IGF-I gene could be considered as a candidate gene of selected carcass and meat quality traits in sheep.

Review: Effects of different growth rates in broiler breeder and layer hens on some productive traits

Genetic selection that has been carried out for several dozen years has led to significant progress in poultry production by improving productive traits and increasing the profitability of broiler breeder and layer hen production. After hatching, broilers and layers differ mainly in feed intake, growth rate, efficiency of nutrient utilization, and development of muscles and adipose tissue. A key role can be played by hormonal mechanisms of appetite control in broilers and layers. The paper discusses the consequences of different growth rates resulting from long-term genetic selection on feed intake, efficiency of nutrient utilization, and development of muscles and adipose tissue, with particular consideration of the hormonal mechanisms of appetite control in broilers and layers. The information presented in this review paper shows that it would be worth comparing these issues in a meta-analysis.

Secretion pathway of liver IGF-1 via JAK2/STAT3 in chick embryo under the monochromatic light

This study reveals mechanism of monochromatic light on the IGF-1 secretion of chick embryo liver. The chick embryos were incubated and exposed to continuous red, green, blue light or a dark environment. Compared to other light-treated groups, green light increased IGF-1 and melatonin concentrations both in plasma and liver, and Mel1a, Mel1b and Mel1c receptors expressions in liver but decreased p-JAK2, p-STAT3 and ROS in liver. IGF-1 had a positive correlation with melatonin, but a negative relevance with p-JAK2 and p-STAT3. In vitro, the IGF-1 level in the hepatocyte supernatant was enhanced by melatonin with lower p-JAK2/p-STAT3 and ROS levels, which was suppressed by Mel1c antagonist but not Mel1a/Mel1b or Mel1b antagonists. AG490 (JAK/STAT inhibitor) promoted role of melatonin-Mel1c modulated IGF-1 secretion. These results suggest the antioxidant effect of melatonin mediated the green light-enhanced IGF-1 secretion of chick embryo liver through Mel1c receptor to inhibit the JAK2/STAT3 pathway.

Integrative effects of feeding Aspergillus awamori and fructooligosaccharide on growth performance and digestibility in broilers: promotion muscle protein metabolism

This study was conducted to show the effect of Aspergillus awamori (AA), fructooligosaccharide (FOS), and combined Aspergillus awamori and fructooligosaccharide (AA + FOS) on growth, digestibility, blood parameters, and expression of some growth-related genes. A total of 60 broiler chicks at the age of 15 d were divided into a control group (n = 15) and 3 treatment groups. The control group was fed a basal diet, and the treatment groups were fed basal diets supplemented with 0.05% AA, 0.05% FOS, and combined of 0.05% AA and 0.05% FOS. Results from measurement of growth performance and digestibility revealed a significant increase in the body weight gain with improved feed conversion rate in the experimental groups. Interestingly, dry matter digestibility (DMD) and crude protein utilization (CPU) were improved. In addition, plasma total cholesterol and low density lipoprotein-cholesterol (LDL-C) were decreased, while plasma high density lipoprotein-cholesterol (HDL-C) was increased by feeding AA, FOS, and AA + FOS. Expressions of growth hormone secretagogue receptor (GHSR), insulin-like growth factor 1 (IGF-1), and insulin-like growth factor 1 receptor (IGF1R) were increased in experimental groups. In conclusion, the supplementation of either Aspergillus awamori or fructooligosaccharide or both improves digestibility and growth performance probably by promoting skeletal muscle protein metabolism.

Polymorphism of insulin-like growth factor 1 gene is associated with breast muscle yields in chickens

Insulin-like growth factor-1 (IGF1) plays an important role in muscle development in chickens. In this study, an F2 chicken population of 362 individuals, obtained from an intercross between high breast muscle yield line males and low breast muscle yield (LB) line females, was constructed for investigating the associations between IGF1 gene and breast muscle yields. The IGF1 sequence was investigated in the grandparents. There were no differences in the exon sequences. However, sequence analysis of the IGF1 promoter revealed a known single nucleotide polymorphism (g.570C>A) in LB line grandparents. PCR - restriction fragment length polymorphism was used for screening the F2 population, which was evaluated for body weight (BW), carcass weight (CW), breast muscle weight (BMW), and breast fillet weight (BFW). Significant associations with the polymorphism were detected for BMW, BFW, BMW% and BFW%, although there were no associations between the polymorphism and BW or CW. The allelic effect on BMW, BFW, BMW% and BFW% acted in additive and dominance modes. We confirmed that the g.570C>A polymorphism is significantly associated with breast muscle yields in the F2 population. Therefore, this polymorphism in the IGF1 gene may help improve breast muscle yields by marker-assisted selection.

Tissue-specific regulation of S6K1 by insulin in chickens divergently selected for growth

In chickens, insulin injection leads to the activation of the early steps of insulin receptor signaling in liver but not in muscles. Paradoxically, muscle p70 S6 kinase (S6K1), a kinase controlling protein synthesis and growth, was markedly activated in response to insulin. The aim of this study was to further investigate S6K1 regulation and activation using chickens divergently selected for growth, i.e. fast- (FGL) and slow- (SGL) growing lines. In the Pectoralis major muscle, insulin stimulated S6K1 phosphorylation on T389 in FGL and SGL chickens, whereas S6K1 phosphorylation on T421/S424 was increased by insulin only in FGL chickens. Moreover, insulin-related increase in muscle S6K1 activity was greater in FGL chickens than in SGL chickens. Surprisingly, liver S6K1 was insulin insensitive in the two genotypes. Such difference of regulation between tissues and between genotypes was not observed for the protein kinase B, which is involved in insulin signaling upstream of S6K1, or for eukaryotic initiation factor 4E-binding protein. Interestingly, insulin-activated a S6K1 downstream target, the ribosomal protein S6, irrespective of tissue, suggesting that a pathway different of the S6K1 cascade may be involved in S6 phosphorylation in chicken liver. In conclusion, the regulation of S6K1 differs between the liver and muscle and between chickens divergently selected for growth. Our results suggest a potential involvement of S6K1 in the control of muscle growth and an open issue concerning S6K1 function in chicken liver.

Genome-Wide Linkage Analysis to Identify Chromosomal Regions Affecting Phenotypic Traits in the Chicken. IV. Metabolic Traits

The current study is a comprehensive genome analysis to detect QTL affecting metabolic traits in chickens. Two unique F(2) crosses generated from a commercial broiler male line and 2 genetically distinct inbred lines (Leghorn and Fayoumi) were used in the present study. The plasma glucagon, insulin, lactate, glucose, tri-iodothyronine, thyroxine, insulin-like growth factor I, and insulin-like growth factor II concentrations at 8 wk were measured in the 2 F(2) crosses. Birds were genotyped for 269 microsatellite markers across the entire genome. The program QTL Express was used for QTL detection. Significance levels were obtained using the permutation test. For the 10 traits, a total of 6 and 9 significant QTL were detected at a 1% chromosome-wise significance level, of which 1 and 6 were significant at the 5% genome-wise level for the broiler-Leghorn cross and broiler-Fayoumi cross, respectively. Most QTL for metabolic traits in the present study were detected in Gga 2, 6, 8, 9, 13, and Z for the broiler-Leghorn cross and Gga 1, 2, 4, 7, 8, 13, 17, and E47 for the broiler-Fayoumi cross. Phenotypic variation for each trait explained by all QTL across genome ranged from 2.73 to 14.08% in the broiler-Leghorn cross and from 6.93 to 21.15% in the broiler-Fayoumi cross. Several positional candidate genes within the QTL region for metabolic traits at the 1% chromosome-wise significance level are biologically associated with the regulation of metabolic pathways of insulin, triiodothyronine, and thyroxine.

Insulin-like growth factor-I gene polymorphism associations with growth, body composition, skeleton integrity, and metabolic traits in chickens

Molecular genetic selection on individual genes is a promising method to genetically improve economically important traits in chickens. A resource population was developed to study the genetics of growth, body composition, skeletal integrity, and metabolism traits. Broiler sires were crossed to dams of 2 diverse, highly inbred lines (Leghorn and Fayoumi), and the F1 birds were intermated by dam line to produce broiler-Leghorn and broiler-Fayoumi F2 offspring. Growth, body composition, skeletal integrity, and hormonal and metabolic factors were measured in 713 F2 individuals. Insulin-like growth factor-I (IGF1) was selected for study as a biological and positional candidate gene. A single nucleotide polymorphism (SNP) was identified between the founder lines in the IGF1 promoter region, and a PCR-RFLP assay was developed. A mixed model was used to statistically analyze associations of IGF1-SNP1 with phenotypic traits. The IGF1-SNP1 had significant associations with most recorded traits, except metabolic traits. Strong interactions between the IGF1 gene and genetic background on growth traits in the 2 F2 populations suggest that genetic interaction is an important aspect for consideration before using the IGF1-SNP1 in marker-assisted selection programs. Several beneficial effects (improved growth, increased breast muscle weight, decreased abdominal fat, and enhanced skeletal integrity) associated with 1 allele indicate the presence of 1 or more loci near IGF1-SNP1 controlling biologically diverse and economically important traits in chickens.

Expression and relationship of the insulin-like growth factor system with posthatch growth in the Korean Native Ogol chicken

Insulin-like growth factors (IGF) act as regulators that modulate proliferation and differentiation of various cells. Also, IGF are involved in metabolism and body growth by regulating the synthesis and degradation of glycogen and proteins in animals. However, the effect of IGF system on body growth in poultry including Korean Native Ogol chickens (KNOC) has not been thoroughly studied. Therefore, this study was performed to investigate the expressions of IGF system and the relationship of IGF with body growth during posthatch growth in KNOC. Sera and organs were collected at hatch and at 1, 3, 5, and 7 wk. The mRNA expressions of IGF, IGF-I receptor, and IGF binding protein (IGFBP)-2 were quantitatively analyzed by reverse transcription (RT)-PCR. The IGF concentrations were measured by heterologous RIA, and the expression of IGFBP-2 was detected by Western ligand blotting. The body weight of KNOC rapidly increased during the experimental period, and increase in breast muscle weight was 5-fold from 1 to 3 wk. Although the circulating IGF-I concentration gradually increased, the level of IGF-I in breast muscle rapidly declined during growth period. The IGF-II expression was not similar to IGFBP-2 during postnatal growth. Moreover, the breast muscle IGF-II concentration was mainly correlated with body growth at 7 wk and breast muscle IGF-I at 1 and 5 wk. Taken together, the present study suggested that the endocrine manner of IGF-I was more important than auto/paracrine actions in body growth of KNOC and that expression of IGF-II was involved in body growth and IGF-I during posthatch growth of KNOC.

Response of broilers selected on carcass quality to dietary protein supply: live performance, muscle development, and circulating insulin-like growth factors (IGF-I and -II)

The effect of dietary protein supply on muscle development and circulating concentrations of insulin-like growth factors (IGF)-I and -II was examined in chickens selected for increased breast yield and decreased fatness (quality, QL) and in its control line (CL). CL and QL chickens were fed isoenergetic diets containing 121.5 or 215.8 g CP/kg during a 12-d period; comparisons were performed at 33 d of age. Birds given the high protein diet grew faster, ate less feed, had lower feed conversion ratio (FCR), and higher muscle weights than their counterparts given the low protein diet. The muscle weight response to protein supply differed between muscles in both lines, with pectoralis major appearing more sensitive than sartorius. The response of the gastrocnemius muscle depended on the line. Selection for carcass quality increased (P < 0.01) body weight, growth rate, feed intake, pectoralis major and sartorius muscle weights, and pectoralis major muscle proportion. There was, however, no line difference in FCR or in sartorius muscle proportion. The weight and proportion of the gastrocnemius muscle were higher (P < 0.05) in the QL than the CL chickens on the high protein diet, but there was no line difference for the low protein diet. Plasma levels of IGF-I, and to a lesser extent IGF-II, were lower (P < 0.01) in protein-restricted chickens. No difference in circulating IGF-II was observed between the lines. Concentrations of IGF-I were higher (P < 0.05) in QL than CL chickens, which may contribute to improved body composition for this genotype.

Genetically caused retarded growth in animals

Growth process of animals is regulated by a multitude of physiological pathways among which components of the somatotropic axis play a key role. A number of severe, simply inherited growth disturbances have been identified in humans, laboratory and farm animals. These disorders are controlled by defective alleles at major loci referring to hormones or hormone receptors, e.g. growth hormone receptor for the recessive sex-linked dwarfism (dw) in chickens and the recessive autosomal Laron-type dwarfism in man, and growth hormone releasing hormone receptor for the recessive "little" mutation (lit) in mice. Apart from these particular cases, growth rate is a quantitative polygenic trait which has a moderate heritability (close to 0.30) and is influenced by prenatal and postnatal maternal effects. Increase in the average coefficient of inbreeding in a population is also known to result in lower growth rate. Divergent selection experiments have shown that upward or downward selection on growth is effective, sometimes with asymmetrical responses, but patterns of changes in underlying physiological traits appear to differ among experiments.

The role of the somatotrophic axis in the metabolism of the chicken

As it is for mammalian species, growth hormone (GH) is indispensable for normal growth and development of avian species. In contrast to mammals, exogenous GH administration has little, if any, potential for improving the growth rate and feed efficiency of rapidly growing broilers; it is more likely to do so in older birds. This is at least partly because of age-related changes in tissue GH-binding activity and GH-receptor mRNA expression. The effects of GH on lipid deposition depends on the age of the bird and pattern of GH administration. Pulsatile, but not continuous, GH administration to older broilers seems to reduce fat deposition. As in rats, the bioactivity of GH might also depend on the pulse-induced cyclicity in GH receptors and GH-binding proteins. In chickens, GH is also a very potent lipolytic hormone, but seems to have no diabetogenic effect, which is reported in mammalian species. Both insulin-like growth factors have apparently no growth-promoting effects in normal growing broilers, but seem to have opposite effects on fat deposition. In contrast to GH, both insulin-like growth factors have a marked hypoglycemic effect. Whether all these effects are direct effects, or are mediated by secondary mechanisms, awaits further investigations.