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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. [ABSTRACT FROM AUTHOR]

The aim of this study was to estimate covariance functions, using B-spline random regression models for body weight (BW), feed intake (FI) and residual feed intake (RFI) in F 2 chickens. Feed intake and body weight were recorded on each bird every week from 2 to 10 weeks of age. The F 2 population was derived from a cross between a fast growing Arian broiler line and Iranian native fowl. Sex, hatch and age in week were fitted as fixed effects and additive genetic and permanent environment as random effects. Variance components were estimated by the means of a Bayesian analysis, using Gibbs sampling. Covariance components for cumulative FI and RFI were obtained as a function of week on test. The heritability estimates for BW ranged from 0.19 to 0.34 and were high at the early ages, decreases with age to a moderate value. A similar pattern was observed for FI, where the heritabilities decreased from 0.29 to 0.12 from the second week to 10th week of age. Estimates of heritabilities for RFI along the growth trajectory ranged from 0.10 to 0.29 and increased over the time. Cumulative FI and RFI had medium to high heritability (0.24 and 0.41, respectively). The posterior means of genetic correlations between BW at different age were moderate to high from 2 to 10 weeks of age, ranging from 0.26 to 0.99. These estimates for phenotypic correlations were lower than the corresponding genetic correlations for all the weeks. The posterior means of genetic correlations between different weeks of age ranged from 0.10 to 0.99 for FI and −0.15 to 0.96 for RFI. The genetic and phenotypic correlations consistently decreased as the time interval increased for all traits. However, for the cumulative FI and RFI traits were increased with increasing the age interval from 2 to 9 weeks of age. The genetic correlations and expected response to indirect selection showed that the optimum test length for FI and RFI can be reduced to 2 weeks without a large loss in overall genetic gain in FI or RFI. In general, spline model showed that there was genetic variation in the BW, FI and RFI curve of individual chicken. The results indicated that random regression models can provide a good description of the data and is recommended for genetic selection in chickens. [ABSTRACT FROM AUTHOR]

The purpose of this study was to perform a meta-analysis comparing the biological efficiency of DL-methionine and L-methionine (DL-Met and L-Met) in broiler nutrition. This analysis was based on a dataset comprising experiment results published in peer-reviewed papers since 2007. All experiments investigated the response of broilers (aged 0–21 d) to different dietary concentrations of DL- and L-Met, achieved by supplementing crystalline Met. A graphical analysis was conducted on the database using ellipses coverage and nonparametric density techniques. Two methods of linear and nonlinear exponential meta-regression analysis were used to determine relative bioavailability based on average daily gain (ADG) and feed conversion ratio (FCR) responses to dietary Met sources. The analyses of ADG and FCR obtained from both linear and exponential models showed a relative difference between the tested methionine sources. The results showed that both ADG and FCR were improved in L-Met compared to DL-Met supplemented diets. Linear regression analysis revealed that DL-Met was 94.97% (for ADG) and 95.63% (for FCR) as efficacious as L-Met (P < 0.01). In contrast, the analysis of the fitted nonlinear exponential model showed that the biological efficiencies of DL-Met were 91.33% and 76.57% of the values for L-Met for ADG (P = 0.01) and FCR (P = 0.09), respectively. Based on the meta-analytical results, an equivalence of relative biological efficiency of DL-Met in comparison with L-Met for young broilers could not be confirmed. [ABSTRACT FROM AUTHOR]