The Genetics For Feed Intake And Efficiency In Laying Periods Of Chicken

Feed contributes to over 60% of the total production costs in the poultry industry. Increasing feed costs and environmental issues of husbandry prompted geneticists to include feed intake and efficiency as selection goals in breeding programs. A trend has developed to prolong the laying cycle, feed efficiency in the late laying period must be addressed accordingly. In this thesis, we constructed an F2 resource population and a nucleus breeding stock. Within each population, we evaluate the genetic parameters of feed intake and efficiency traits, and then performed genome-wide association study (GWAS) to explore the genetic basis of traits.Laying records on 1,534 F2 hens, derived from a reciprocal cross between White Leghorns and Dongxiang blue-shelled chickens, were used to estimate genetic parameters for residual feed intake (RFI),feed conversion ratio (FCR), daily feed intake (FI), metabolic BW (MBW), BW gain (BWG), and daily egg mass (EM) at 37 to 40 (TI) and 57 to 60 wk age (T2), respectively. Genetic analysis was subsequently conducted with the Al-REML method using an animal model. Estimates for heritability of RFI, FCR, and FI were 0.21, 0.19, and 0.20 in T1, and 0.29, 0.13, and 0.26 in T2, respectively. In T1 and T2, RFI showed high and positive genetic correlations with FCR (0.51, 0.43) and FI (0.72, 0.84), whereas the genetic correlation between FI and FCR was very low (-0.09, 0.11). Genetically, negative correlations were found between RFI and its component traits (-0.01 to -0.47). In addition, high genetic correlations, from 0.76 to 0.94, were observed between T1 and T2 for RFI, FCR, and FI, suggesting that feed efficiency traits in the 2 stages had a similar genetic background. The results indicate that selection for low RFI could reduce FI without significant changes in EM, while selection on FCR will increase EM. The present study lays the foundation for genetic improvement of feed efficiency during the laying period of chickens.A total of 1534 F2 hens were genotyped using the chicken 600 K single nucleotide polymorphism(SNP) genotyping array. Univariate, bivariate, and conditional genome-wide association studies (GWAS)were performed for FI, RFI and FCR using GEMMA (a genome-wide efficient mixed model association algorithm) software. The statistical significance threshold for association was inferred by the simpleM method. We identified eight genomic regions that each contained at least one genetic variant that showed a significant association with FI. Genomic regions on Gallus gallus (GGA) chromosome 4 coincided with known quantitative trait loci (QTL) that affect feed intake of layers. Of particular interest, eight SNPs on GGA1 in the region between 169.23 and 171.55 Mb were consistently associated with FI in both univariate and bivariate GWAS, which explained 3.72 and 2,57 % of the phenotypic variance of FIl and FI2,respectively. The CAB39L and GIP can be considered as promising candidate genes for FI1 and FI2,respectively. For RFI, a haplotype block on GGA27 harbored a significant SNP associated with RFI2. The major allele of rs315135692 was favorable for a lower RFI, with a phenotypic difference of 3.35 g/day between opposite homozygous genotypes. Strong signals on GGA1 were detected in the bivariate GWAS for FCR. The results demonstrated the polygenic nature of feed intake. GWAS identified novel variants and confirmed a QTL that was previously reported for feed intake in chickens. Genetic variants associated with feed efficiency may be used in genomic breeding programs to select more efficient layers.In the present study, we measured daily feed intake (FI), residual feed intake (RFI) and feed conversion ratio (FCR) of 808 hens during 81-82 weeks of age to evaluate genetic properties and then used a genome-wide association study (GWAS) to reveal the genetic determinants. The heritability estimates for the investigated traits were medium and between 0.15 and 0.28 in both pedigree- and genomic-based estimates,whereas the genetic correlations among these traits were high and ranged from 0.49 to 0.90. Three genome-wide significant SNPs located on chromosome 1 (GGA1) were detected for FCR. Linkage disequilibrium(LD) and conditional GWA analysis indicated that these 3 SNPs were highly correlated with one another,located at 13.5 5-45.16 Kb upstream of gga-miR-15a. Results of quantitative real-time polymerase chain reaction (qRT- PCR) analysis in liver tissue showed that the expression of gga-miR-15a was significantly higher in the high FCR birds than that in the medium or low FCR birds. Bioinformatics analysis further revealed that gga-mir-15a could act on many target genes,such as forkhead box 01 (FOXO1) that is involved in the insulin-signaling pathway, which influences nutrient metabolism in many organisms.Additionally, some suggestively significant variants, located on GGA3 and GGA9, were identified to associate with FI and RFI. This GWA analysis was conducted on feed intake and efficiency traits for chickens and was innovative for application in the late laying period. Our findings can be used as a reference in the genomic breeding programs for increasing the efficiency performance of old hens and to improve our understanding of the molecular determinants for feed efficiency.