The experiment aimed to study effects of dietary metabolizable energy (ME) and crude protein (CP) levels alone and in interaction on performance, pectoral muscle composition and gut microbiota in native growing chickens. A total of 648 10-wks-old Beijing-You Chicken (BYC) female chickens were randomly allocated to 9 groups with 6 replicates per group and 12 chickens per replicate, and the chickens were fed with a 3 × 3 factorial diets (3 levels of dietary ME: 11.31 MJ/kg, 11.51 MJ/kg, 11.71 MJ/kg; and 3 levels of dietary CP: 14%, 15%, 16%). The results showed that dietary ME and CP levels didn't affect average feed intake (AFI), body weight gain, feed gain ratio (P > 0.05), but ME level significantly affected the AFI (P < 0.05); mortality rate of 11.31 MJ/kg group was the highest (P < 0.05). Dietary ME, CP levels, and the interaction significantly affected pectoral CP and crude fat (CF) content of the growing chickens (P < 0.01). Dietary CP level had opposite effects on pectoral CP and CF content (P < 0.01). The 16% CP increased the pectoral CF content, which may have a negative impact on meat flavor. Dietary ME level affected 11 types of pectoral free amino acids (FAA) contents, including aspartic acid, L-threonine (P < 0.05), also amino acid classification, for example, total amino acid (TAA) and essential amino acid (EAA) content (P < 0.05). The 11.51 MJ/kg group had the highest TAA, EAA, delicious amino acid (DAA) content and EAA percentage (P < 0.05), while 11.31 MJ/kg group had the lowest bitter amino acid (BAA) content and BAA percentage and the highest fresh and sweet amino acid (FSAA) percentage (P < 0.05). Dietary CP level significantly affected glutamine and tyrosine content (P < 0.05). The interaction of dietary ME and CP level affected C20:3n6 content, saturated fatty acid (SFA), and unsaturated fatty acid (UFA) percentage (P < 0.05). The CP level significantly affected SFA percentage (P < 0.05). The 16% CP level increased the diversity of gut microbiota, but at the same time increased the relative abundance of Proteobacteria (P < 0.05), which is a sign of microbiota disorder. The increase of dietary ME level resulted in a gradual decrease in the diversity and relative abundance of gut microbiota. In conclusion, the present study suggested that the medium dietary ME (11.51 MJ/kg) and low CP (14–15%) levels can be helpful for enhancing pectoral muscle composition, increase meat quality such as flavor and nutritional value, and benefit for gut microbiota in native growing chickens.

The physical properties, free amino acids, and metabolites of Beijing-You chicken (BYC) breast meat aged 90, 120, and 150 days were analyzed to investigate the flavor changes with age. The shear force and intramuscular fat increased from 90 to 120 days significantly. The contents of total free amino acids and essential amino acids decreased from 90 to 120 days significantly. No significant differences were detected between 120 and 150 days. The contents of sweet amino acids, bitter amino acids, and umami amino acids showed no significant differences between different ages. In addition, GC-MS and LC-MS were integrated for metabolite detection in breast meat. A total of 128, 142, and 88 differential metabolites were identified in the comparison groups of 120 d vs. 90 d, 150 d vs. 90 d, and 150 d vs. 120 d. Amino acids and lipids were the main differential metabolites. The pathway analysis showed that arginine biosynthesis, histidine metabolism, purine metabolism, and cysteine and methionine metabolism were the main pathways involved in flavor formation during BYC development. It was also found that the metabolites associated with flavor, such as methionine, cysteine, glucose, anserine, arachidonic acid, and glycerol 1-phosphate, were significantly affected by age.

Chicken age contributes to the meat characteristics; however, knowledge regarding the pathways and proteins associated with meat quality and muscle development are still scarce, especially in chicken thigh meat. Hence, the objective of this study was to elucidate the intricate relationship between these traits by liquid chromatography mass spectrometry at three different ages. A total of 341 differential expressed proteins (DEPs) were screened out (fold change ≥ 1.50 or ≤0.67 and p < 0.05) among 45 thigh meat samples (15 samples per age) of Beijing-You chicken (BYC), collected at the age of 150, 300, or 450 days (D150, D300, and D450), respectively. Subsequently, based on the protein interaction network and Markov cluster algorithm (MCL) analyses, 91 DEPs were divided into 26 MCL clusters, which were associated with pathways of lipid transporter activity, nutrient reservoir activity, signaling pathways of PPAR and MAPK, focal adhesion, ECM-receptor interaction, the cell cycle, oocyte meiosis, ribosomes, taurine and hypotaurine metabolism, glutathione metabolism, muscle contraction, calcium signaling, nucleic acid binding, and spliceosomes. Overall, our data suggest that the thigh meat of BYC at D450 presents the most desirable nutritional value in the term of free amino acids (FAAs) and intramuscular fat (IMF), and a series of proteins and pathways associated with meat quality and development were identified. These findings also provide comprehensive insight regarding these traits across a wide age spectrum.

This study aimed to investigate the effects of dietary crude protein (CP) and lysine levels on growth performance, slaughter performance, meat quality, and myofiber characteristics of slow-growing chicken. A 3 × 3 factorial experiment was arranged, and the chickens were fed with 3 levels of dietary CP (16.0%, 17.0%, 18.0%) and 3 levels of dietary lysine (0.69%, 0.84%, 0.99%). A total of 540 8-week-old Beijing-You Chicken (BYC) female growing chickens were randomly allocated to 9 groups, 5 replicates per group, and 12 chickens per replicate. The birds were randomly allocated to one of the 9 experimental diets. Growth performance, slaughter performance, meat quality, and myofiber characteristics were determined at 16 weeks of age. The results showed that dietary CP level and the interaction of dietary CP and lysine levels affected average feed intake (AFI) (p < 0.05). The AFI in the 16.0% CP and 17.0% CP groups was higher than in the 18.0% CP group (p < 0.05). Dietary CP levels significantly affected body weight gain (BWG) (p < 0.05) at 9 to 16 weeks. The 18.0% CP group had the highest BWG (93.99 g). Dietary CP levels affected the percentage of leg muscle yield, and the percentage of leg muscle yield of the 16.0% CP group was significantly lower than that in the other two groups (p < 0.05). Dietary CP and lysine levels alone and their interactions did not affect pH_24h, drip loss, and cooking loss of breast muscle (p > 0.05). The shear force of the 18.0% CP group (29.55 N) was higher than that in the other two groups (p < 0.01). Dietary CP level affected myofiber characteristic (p < 0.01), with the lowest myofiber density (846.35 p·mm⁻²) and the largest myofiber diameter (30.92 μm) at 18.0% CP level. Dietary lysine level affected myofiber diameter, endomysium thickness, perimysium thickness (p < 0.01), with the largest myofiber diameter (29.29 μm) obtained at 0.84% lysine level, the largest endomysium thickness (4.58 μm) at 0.69% lysine level, and the largest perimysium thickness (9.26 μm) at 0.99% lysine level. Myofiber density was negatively correlated with myofiber diameter and endomysium thickness (R = −0.883, R = −0.523, p < 0.01); perimysium thickness had a significant negative correlation with shear force (R = −0.682, p < 0.05). Therefore, reducing dietary CP level and adding appropriate lysine can reduce myofiber diameter and increase perimysium thickness, reducing shear force and improving meat tenderness. A high lysine level (0.99%) in the low-CP (16.0%) diet can improve meat tenderness by regulating the myofiber characteristic without affecting production performance.

This study aimed to investigate the effects of dietary calcium (Ca) and non-phytate phosphorus (NPP) levels alone and in interaction on performance, egg quality, lipid metabolism, antioxidant capacity and follicular development in aged local laying hens. A total of 900 44-week-old Beijing You Chicken (BYC) laying hens with an average body weight of 2.13 ± 0.12 kg were randomly allocated to nine groups (100 hens/group, four replicates of 25 hens). A 3 × 3 factorial design was used with Ca at 3.0%, 3.4%, 3.8% and NPP at 0.31%, 0.36%, 0.41%, respectively. After 1 week of adaptation, the trial lasted from 45 to 58 weeks of age. The results showed that dietary Ca and the NPP level alone did not affect the egg-laying rate of BYCs during 45–58 weeks (p > 0.05), but their interaction affected egg mass (EM, p = 0.049). The group with 3.0% Ca and 0.31% NPP exhibited the highest EM (0.22 kg). At 52 weeks of age, the dietary Ca level affected yolk color (YC): 3.4% Ca and 3.6% Ca increased YC (p < 0.05). Dietary 0.41% NPP decreased YC (p < 0.05). The Ca and NPP interaction affected the albumen height (AH), Haugh unit (HU) and YC (p < 0.05). The group with 3.0% Ca and 0.41% NPP had the highest AH (5.14) and HU (73.46). At 58 weeks of age, 3.4% Ca indicated the lowest YC (p < 0.05). Moreover, 0.36% NPP had the lowest YC and the highest RYW (p < 0.05). Significant Ca × NPP interactions were observed for eggshell thickness (EST), AH, HU, YC, and egg grade (EG) (p < 0.05). The group with 3.0% Ca and 0.41% NPP exhibited the highest AH, HU, YC, and EG. The Ca × NPP interaction affected high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) content (p < 0.05). Dietary 0.41% NPP increased serum malondialdehyde (MDA) content (p = 0.020). The group with 3.0% Ca and 0.41% NPP had the lowest serum LDL-C (p < 0.05). Dietary Ca, the NPP level alone, and their interaction might not affect the number of large yellow follicles and graded follicles at 58 weeks of age (p > 0.05). The 0.36% NPP and 0.41% NPP increased the number of small yellow follicles (p = 0.021). The group with 3.4% Ca and 0.36% NPP had the highest number of small yellow follicles (25.75 ± 4.34, p = 0.033). In summary, the dietary Ca and NPP interaction, rather than Ca or the NPP level alone, contributed to egg mass, egg quality, lipid metabolism and small yellow follicles in the late laying period. An excessive NPP level (0.41%) may not bring additional benefits to the late laying hens’ performance and could lead to increased peroxidation in the aging local laying hens.

Body weight variation within a breed may be associated with meat flavor in chickens, but its relationship with flavor-related precursor composition across developmental stages remains unclear. Here, integrated lipidomics and metabolomics were applied to compare breast muscle from Beijing-You chickens sampled from the same cohort at 90, 110, 130, and 150 d in a stage-wise design. At each stage, higher-body-weight (HBW) and lower-body-weight (LBW) groups were independently defined from the upper and lower tails of the body weight distribution at that age. A total of 440, 259, 161, and 324 differential lipids, as well as 491, 257, 291, and 402 differential metabolites, were identified at the four stages, respectively. However, only 23 lipids and 3 metabolites were shared across all stages, indicating that metabolic differences between the HBW and LBW groups varied markedly across developmental stages. Differential lipids were mainly distributed among phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine, while glycerophospholipid metabolism was consistently identified in both lipidomic and metabolomic analyses. Notably, a key transition was observed between 110 and 130 d, during which the predominant direction of PUFA-like differential lipids shifted from HBW to LBW predominance. Representative differential metabolites included N-acetyl-L-methionine, N-methyl-L-glutamic acid, and γ-glutamyl-5-hydroxytryptophan, suggesting alterations in amino acid- and peptide-related metabolism. Overall, these findings provide insight into stage-dependent variation in flavor-related precursor composition within a breed across developmental stages. However, their direct contribution to flavor remains to be validated.