The chicken growth hormone (cGH) gene plays a crucial role in controlling growth and metabolism, leading to potential correlations between cGH polymorphisms and economic traits. In this study, DNA from four divergent chicken breeds were screened for single nucleotide polymorphisms (SNPs) in the cGH gene using denaturing high-performance liquid chromatography and sequencing. A total of 46 SNPs were identified, of which 4 were in the 5' untranslated region, 1 in the 3' untranslated region, 5 in exons (two of which are nonsynonymous), with the remaining 36 in introns. The nucleotide diversity in the cGH gene ( theta = 2.7 x 10(-3)) was higher than that reported for other chicken genes, even within the same breeds. The associations of five of these SNPs and their haplotypes with chicken growth and carcass traits were determined using polymerase chain reaction-restriction fragment length polymorphism analysis in a F2 resource population cross of two of the four chicken breeds (White Recessive Rock and Xinghua). This analysis shows that, among other correlations, G+1705A was significantly associated with body weight at all ages measured, shank length at three of four ages measured, and average daily gain within weeks 0 to 4. Thus, this cGH polymorphism, or another polymorphism that is in linkage disequilibrium with G+1705A, appears to correspond to a significant growth-related quantitative trait locus difference between the two breeds used to construct the resource population.

Thirty single nucleotide polymorphisms (SNP) and one 6-bp insertion-deletion (indel) from 8 genes of somatotropic axis were used to study the association with chicken fatness and muscle fibers. The allele frequency difference between Xinghua and White Plymouth Rock chickens was observed, and their effects on fatness and muscle fiber traits were also evaluated by linkage analyses. The G143831A (G+1705A) SNP of the growth hormone (GH) gene was related to fat width, and the G144762A (G+119A) SNP of the GH gene was significantly associated with abdominal fat pad weight, abdominal fat pad ratio, and crude fatty content of the breast muscle. The 6-bp indel of the growth hormone secretagogue receptor (GHSR) gene was significantly linked with the fat traits. The C51978309T SNP of the insulin-like factor-I (IGF-I) gene was significantly linked with the transversal area of the leg muscle fiber and transversal area of the breast muscle fiber. There was significant linkage between the insulin (INS) gene and 2 traits of the transversal area of transversal area of the leg muscle fiber and transversal area of the breast muscle fiber. Association of 30 SNP and one 6-bp indel from 8 genes of somatotropic axis with chicken fatness and muscle fiber traits was analyzed in the present study. The GH, GHSR, and leptin receptor genes were significantly related to chicken fatness. The INS and IGF-I genes were linked with muscle fiber density. Therefore, the genes of somatotropic axis not only affected chicken growth and body composition but also were associated with fatness and muscle fiber traits.

Broodiness is a polygenic trait controlled by a small number of autosomal genes. Vasoactive intestinal peptide receptor-1 (VIPR-1) gene could be a candidate of chicken broodiness, and its genomic variations and genetic effects on chicken broodiness traits were analyzed in this study. The partial cloning and sequencing of the VIPR-1 gene showed that the average nucleotide diversity was 0.00669 +/- 0.00093 in Red Jungle Fowls (RJF), and 0.00582 +/- 0.00026 in domestic chickens. One hundred twenty-eight variation sites were identified in the 11,136-bp region of the chicken VIPR-1 gene. Twenty variation sites were genotyped using PCR-RFLP or PCR method to analyze average diversity, linkage-disequilibrium pattern, and haplotype structure in RJF, Xinghua chickens, Ningdu Sanhuang chickens, Baier Huang chickens, and Leghorn Layers. The RJF, Xinghua, Ningdu Sanhuang, and Baier Huang exhibited distinct characteristic of decreasing r(2) value over physical distance. Haplotype analyses showed that some variation sites of the 27-kb region from exon 6 to exon 11 could be associated with broodiness. The distribution of genotypic and allelic frequencies, and heterozygosities in the above 5 populations showed that A-284G, A+457G, C+598T, D+19820I, C+37454T, C+42913T, and C+53327T might be associated with broodiness. The 7 sites and the other 4 sites were genotyped in 644 NDH individuals under cage condition and were used for association analyses between each site and chicken broodiness traits. A significant association (P < 0.05) was found between C+598T in intron 2 and broody frequency (%). Another significant association (P < 0.05) was found between C+53327T and duration of broodiness, in which allele C was positive for DB.

Ghrelin (GHRL) and its receptor (GHSR) are involved in various bioactivities. In this study, the complete cDNA and 5′ flanking region of the duck GHRL (dGHRL) gene and a 3717 bp fragment of the duck GHSR (dGHSR) gene were obtained. A total of 19, 8, 43, and 48 SNPs identified in 2751, 1358, 3671, and 3567 bp of the chicken GHRL (cGHRL), chicken GHSR (cGHSR), dGHRL, and dGHSR genes, respectively. Both cGHRL and dGHRL were expressed predominantly in the proventriculus, whereas the highest mRNA levels of cGHSR and dGHSR were detected in the breast muscle and pituitary. Association analysis showed that C-2047G, A-2355C, and A-2220C of the cGHRL gene were significantly associated with abdominal fat weight (AFW; P = .01), crude protein content of leg muscle (CPCLM; P = .02), and CPCLM (P = .0009), respectively. C-1459T of the cGHSR gene was also significantly associated with CPCLM (P = .0004). C-729T of dGHRL and A3427T of dGHSR were both significantly associated with subcutaneous fat thickness (SFT; P = .04). It was indicated by this study that the GHRL and GHSR genes were related to fat deposition in both chicken and duck.