Growth hormone secretagogue receptor (GHSR) modulates many physiological processes by binding to its ligand, as well as transforming growth factor-beta 2 (TGFB2) regulates cell growth and development in animals and, therefore, are candidate genes for performance in chickens. In the current study, single nucleotide polymorphisms of GHSR C3286 > T and TGFB2 T(-640) > C were genotyped in sire and dam lines of a broiler chicken to evaluate the association with the growth and body composition traits. Least squares means analysis showed that the GHSR C3286 > T SNP was significantly (P < 0.01) associated with growth (DFI and ADG) and body composition traits (AFW and %AFW). In addition, the TGFB2 T(-640) > C SNP was associated with ADG (P < 0.05) and DFI and body composition traits (DW, LBW, BAKWT, %BMW, %HNDWT and %CW) (P < 0.01). Significant associations of the single nucleotide polymorphisms (SNPs) on the traits reported in the present study might be the distinct usage of codons in avian, or relating to an enhancer element and modulating the expression of the gene in chicken. The data indicated that these SNPs could be valuable genetic elements for selection of chickens for better performance in the population.

The Avian Uncoupling Protein (avUCP) belongs to the mitochondrial anion transporter family. It has a pivotal homeostatic mechanism that associated with energy regulation and lipid metabolism. The avUCP considered as a candidate gene for chicken growth-related traits according to its predominant expression is in skeletal muscle. To address genetic distance pattern of UCP3 between mammalian and avian species, sequence similarity analysis using the protein alignment of UCP3 identified the high amino acid identity between the species and complementarily detected two protein conserved regions which are known as the ADP/ATP transporter translocase and the Mitochondria-carrier. Likewise, for mutation detection, samples were genotyped, afterward PCR-SSCP method implemented. In addition, association analysis was performed for investigating single nucleotide polymorphism within the UCP3 gene relating to the given economic traits. A detected polymorphic site, on the promoter region of UCP3 (-40 T/A substitution), has displayed significant influences on the Feed Conversion Rate (FCR), Residual Feed Intake (RFI), Average Daily Gain (ADG), and Carcass Weight (CW%). In the case that, birds with genotype AA had better FCR, ADG, RFI as compared to the genotype BB and birds with genotype AA revealed a higher CW% as compared to the genotype BB. According to the obtained results from the in-silico survey, Myoblast determination protein (MyoD) was predicted as a best-matched transcription factor with a consensus sequence harboring the-40 T/A-novel SNP-in the promoter region of UCP3, where might be responsible for phenotypic variation between two genotypes. In conclusion, the result suggests important roles for UCP3 polymorphism in feed efficiency and growth traits which is better to be used in broiler chicken breeding programs.