Transcriptomic analysis of thigh muscle of Lueyang black-bone chicken in free-range and caged feeding.

Lueyang black-bone chicken is free-range in hilly areas and has unique genetic characteristics and excellent muscle quality. However, the molecular mechanisms of breeding mode influence growth and meat quality in Lueyang black-bone chicken are still unclear. Here we analyzed the meat quality and transcriptome data of thigh muscle by comparing free-range and caged modes at the age of 60 and 120 days in Lueyang black-boned chicken. The results demonstrated that the free-range mode could improve the pH value, tenderness, and reducing the hardness of the thigh muscle. Intramuscular fat (IMF) content of the thigh muscle was markedly higher in the caged chickens compared with free-range animals at the age of 60 days. Functional pathway analysis illustrated that tight junction signaling was associated with the formation of slow-twitch fibers in free-range chickens at age of 120 days. All research data proved that the free-range mode could improve muscle quality by promoting the formation of slow-twitch fibers and IMF in thigh muscle in Lueyang black-bone chicken. Based on the animal benefit and healthy, the free-range feeding should be considered during the breeding process of broiler chicken. The results provide good knowledge of the functional molecular mechanisms associated with muscle quality in Lueyang black-bone chicken.

The complete mitochondrial genome and molecular phylogeny of Lueyang black-bone chicken.

1. The objectives of the current study were to investigate the mitochondrial genome and molecular phylogeny of Lueyang black-bone chicken, and  provide  molecule base to preserve and explore the specific chicken strain. 2. Based on sequencing and clustering, the complete mitochondrial DNA map and sequences of Lueyang black-bone chicken were revealed, and two phylogenetic trees of Lueyang black-bone chickens based on D-loop sequences and the mitochondrial genome were constructed. 3. The results showed that the complete mitochondrial genome of Lueyang black-bone chickens is 16,784bp in size, consisting of 22 transfer RNA genes, two ribosomal RNA genes, 13 protein-coding genes, and one non-coding control region. The base composition of the complete mtDNA sequence is 30.28% for A, 23.78% for T, 32.42% for C, 13.52% for G. Additionally, 10 haplotypes of D-loop sequences in 32 Lueyang black-bone chickens were detected, which were distributed into 4 clades (A, B, C and E). 4. It was concluded that genetic diversity is wide in Lueyang black-bone chickens, and this strain has multiple maternal origins from different regions in China and neighbouring regions.

A genome-wide scan to identify signatures of selection in Lueyang black -bone chicken.

Lueyang black-bone chicken is a domestic breed in China. The genetic mechanism of the formation of important economic traits of this breed has not been studied systematically. Therefore, in this study, whole genome resequencing was used to systematically analyze and evaluate the genetic diversity of the black-feather and white-feather populations, and to screen and identify key genes related to phenotypes. The results of principal component analysis and population structure analysis showed that Lueyang black-feathered chickens and white-feathered chickens could be divided into 2 subgroups, and the genetic diversity of black-feathered chicken was richer than that of white-feathered chickens. Linkage disequilibrium analysis also showed that the selection intensity of black-feathered chickens was lower than for white-feathered chickens, which was mainly due to the small population size of white-feathered chickens and a certain degree of inbreeding. Fixation index (FST) analysis revealed that the candidate genes related to feather color traits were G-gamma, FA, FERM, Kelch, TGFb, Arf, FERM, and melanin synthesis-related gene tyrosinase (TYR). Based on Kyoto Encyclopedia of Genes and Genomes enrichment analysis, Jak-STAT, mTOR, and TGF-ß signaling pathways were mainly related to melanogenesis and plume color. The findings of this study supported important information for the evaluation and protection of chicken genetic resources and help to analyze the unique genetic phenotypes such as melanin deposition and feather color of Lueyang black-bone chicken. Additionally, it could provide basic research data for the improvement and breeding of Lueyang black-bone chicken with characteristic traits.

Effects of Different Rearing Systems on Lueyang Black-Bone Chickens: Meat Quality, Amino Acid Composition, and Breast Muscle Transcriptome.

The quality of poultry products depends on genotype, rearing system, and environment. The aim of this study was to investigate the effects of different rearing systems on meat quality, amino acid composition, and breast muscle transcriptome from Lueyang black-bone chickens. Lueyang black-bone chickens (n = 900) were randomly divided into three groups (cage, flat-net, and free-range groups), with three replicates per group (100 chickens per replicate). At 16 weeks, a total of 36 healthy chickens (six males and six females per group) were collected, and their breast muscles were sampled to detect meat quality parameters, amino acid composition, and fatty acid contents. Furthermore, breast muscles from six random hens in each group were used for RNA-seq analysis. The results revealed that the values of pH, shear force, inosine monophosphate (IMP), palmitic acid, and linoleic acid in the free-range group were significantly higher than those in the caged group (p < 0.05). Fat content in the free-range group was significantly lower than in the caged and flat-net groups (p < 0.05). Glutamate (Glu) levels, the amino acid crucial for the umami taste, was significantly higher in the free-range group than in the caged group (p < 0.05). Meanwhile, there was no significant difference between the free-range and flat-net groups (p > 0.05). The breast muscle transcriptome results showed that there were 291, 131, and 387 differently expressed genes (DEGs) among the three comparison groups (caged vs. free-range, flat-net vs. caged, and flat-net vs. free-range, respectively) that were mainly related to muscle development and amino acid metabolism pathways. To validate the accuracy of the transcriptome data, eight genes (GOS2, ASNS, NMRK2, GADL1, SMTNL2, SLC7A5, AMPD1, and GLUL) which relate to fat deposition, skeletal muscle function, and flavor formation were selected for Real-time Quantitative PCR (RT-qPCR) verification. In conclusion, these results suggested that rearing systems significantly influenced the meat quality and gene expression of Lueyang black-bone chickens. All the data proved that free-range and flat-net systems may provide better flavor to consumers by affecting the deposition of flavor substances and the expression of related genes. These findings will provide a valuable theoretical basis for the rearing system selection in the poultry industry.