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.

Based on resource allocation theory, ignoring importance of immunity, and focus on growth and feed efficiency (FE) traits in breeding plans may lead to serious weakness in immune system performance. However, in poultry the adverse effects of selection for FE on the immune system are unclear. Therefore, an experiment was conducted to study the trade-off between FE and immunity using a total of 180 high-performing specialized male chickens from a commercial broiler line which were selected over 30 generations for growth (body weight gain, BWG) and FE (residual feed intake, RFI). Birds were reared for 42 d and 5 FE-related traits of the birds in the last week were considered including daily feed intake (DFI), feed conversion ratio (FCR), residual feed intake (RFI), residual BW gain (RG), and residual intake and gain (RIG). For all 180 chickens, immune system performance including humoral immune response, cell-mediated immunity (CMI), and the activity of lysozyme enzyme (L. activity) as innate immunity was measured. After ascending sort of each FE records, 10% of higher records (H-FE: N = 18) and 10% of lower records (L-FE: N = 18) were determined, and immunity between L-FE and H-FE groups were compared. Moreover, L-BWG and H-BWG were analyzed because BWG is one of components in the FE formula. Performance of the immune system was not statistically different for CMI in none of the studied FE groups. Moreover, high and low groups for DFI and BWG were not different regarding the immunity of the birds. Antibody titers against Newcastle disease virus (NDV) were different between low and high groups of FCR, RG, and RIG. Likewise, SRBC-derived antibodies were significantly different between RFI groups. Rather than humoral immunity, RIG had adversely effect on the innate immunity. Results of the present study showed that although RIG is a more appropriate indicator for FE, choosing for high RIG can weaken the performance of the both humoral and innate immune systems, while RFI had fewer adverse effects.