Body weight performance
Statistical analysis revealed that the average body weight of the 130 Muchuan Black-Boned Chickens was 1,757 g, with a coefficient of variation (CV) of 8.76%, indicating a normal distribution. The average body weight was 1,998.5±10.2 g for the high-weight group and 1,337.5±11.5 g for the low-weight group. The independent-sample
t-test showed a statistically significant difference in body weight between group W and group B (
P<0.01).
Sequencing data quality control
This study performed high-throughput 16S rRNA gene sequencing on intestinal microbial samples from the muchuan black-boned chicken in groups W and B, yielding a total of 1,623,456 raw reads. As shown in Table 1, the number of raw reads before quality control ranged from 57,013 to 90,346, while the number of clean reads after quality control ranged from 54,601 to 86,260, with an average sequencing coverage efficiency of 94.57±1.9%. The average sequence length was 252.7 nt, the Q20 value ranged from 74.66% to 88.21% and the GC content remained stable between 52.68% and 53.42%. These results indicated that the sequencing quality was high, the data were valid and reliable and all samples met the requirements for subsequent bioinformatics analysis.
Dilution curve analysis
A certain amount of sequencing data is randomly selected from the samples and the number of OTUs is counted. The dilution curve is constructed by the amount of sequencing data and the number of corresponding species, so as to describe the curve of sample diversity within the group. OTU clustering results showed that a total of 2102 OTUs were obtained with 97% sequence similarity as the threshold and the coverage index of all samples was above 99%. According to Fig 1, as the number of sequences increases, the dilution curve of each sample gradually tends to be gentle and the number of newly detected OTUs decreases. This indicates that the sequencing data volume in this study was adequate and the sequencing depth was sufficient to reflect the species richness within the samples, which ensured the accuracy and reliability of the analysis results
(Caporaso et al., 2010).
Gut microbiota community composition
The community composition information of each sample at different taxonomic levels was counted to obtain the annotation results of species at the five taxonomic levels of phyla, class, order, family and genus. At the phylum level, the top five in abundance were
Firmicutes,
Proteobacteria,
Bacteroidetes, Actinobacteria and Tenericutes (Fig 2). The abundance of
Firmicutes was highest, accounting for more than 40% of all samples. This microbial community composition was consistent with the gut microbial structure of Jiangxi local chicken, Tibetan chicken and other local chicken breeds
(Li et al., 2024), indicating that
Firmicutes and
Bacteroidetes are the core groups of poultry intestinal microbes. The average value of
Firmicutes/
Bacteroidetes ratio (F/B) in group W was 4.66, which was higher than 3.62 of the group B. The F/B ratio is an important indicator reflecting the relationship between gut microbiota and host energy metabolism. A higher F/B ratio is helpful to improve energy utilization efficiency and promote weight gain
(Turnbaugh et al., 2006; Sommer and Bäckhed, 2013). The
Firmicutes phylum can secrete digestive enzymes such as cellulase and amylase to promote the degradation and absorption of carbohydrates in feed, thereby improving energy utilization efficiency; while the Bacteroidetes phylum mainly participates in the metabolism of proteins and polysaccharides. An excessively high relative abundance of this phylum may reduce the efficiency of energy conversion, thereby inhibiting weight gain (
Sommer and Bäckhed, 2013;
Bäckhed et al., 2004;
Yadav and Jha, 2019).
At the family level, the microbial community structure in group W was relatively stable (Fig 3). The
Lactobacillaceae and
Ruminococcaceae families maintained high abundance in each sample in group W and were one of the core dominant families in group W. In contrast, the microbial community structure in group B samples varied greatly among individuals, with the dominant bacterial families varying significantly among individuals. The results showed that the gut microbial community structure of high weight Muchuan Black-Bone chicken was more stable. As a typical beneficial flora in the gut,
Lactobacillaceae can produce lactic acid, reduce the pH value of the gut, inhibit the proliferation of harmful bacteria such as
Escherichia coli, promote the repair of intestinal mucosal barrier, improve the efficiency of nutrient absorption and then promote the growth of the host (
Pessione, 2012;
Zhang et al., 2025). Previous research on Muchuan Black-Boned chickens indicated that gut microbiota composition is also associated with skin color
(Liao et al., 2024). Furthermore, probiotics belonging to
Lactobacillus strains have been shown to enhance growth performance by improving gut health and nutrient digestibility
(Shawky et al., 2025; Jinturkar et al., 2009). In this study,
Lactobacillaceae were enriched in the high-weight group, suggesting they may serve as potential probiotics for local chicken breeds.
Ruminococcaceae can participate in the degradation of dietary fiber and the synthesis of short chain fatty acids (SCFAs). As an important metabolite of intestinal microorganisms, SCFAs can not only provide energy for the host, but also regulate intestinal immune function, improve intestinal health and indirectly affect the growth performance of the host (
Louis and Flint, 2009;
Canfora et al., 2015).
Alpha and beta diversity analysis
Alpha diversity analysis showed that the Goods coverage index of all samples exceeded 0.996, indicating sufficient sequencing depth (Table 2). The observed species, Shannon index, Simpson index and Goods_coverage did not differ significantly between the B and W groups (P>0.05). However, the Chao1, ACE and PD_whole_tree indices, were significantly higher in the B group than in the W group (P<0.05). These findings demonstrate that samples in group B possess a greater diversity of gut microbial species, higher community richness and more extensive phylogenetic diversity.
In beta diversity studies, the Weighted Unifrac distances among samples ranged from 0.137 to 0.206 in group W (Fig 4), suggesting similar microbial community structures and stable community composition within the group. In contrast, the distances for group B ranged from 0.420 to 0.493, indicating significant variations in microbial community composition and structure among samples, as well as poor intra-group community stability.
Unweighted UniFrac distance was used for PCoA analysis. The results showed that the samples of the W group and B group were significantly separated (Fig 5). The sample points in group W are mainly distributed on the left side of the graph (PC1 negative value area) and the clustering degree of sample points in the group is high, indicating that the similarity of bacterial community structure in group W is high. The sample points in group B are mainly distributed on the right side of the map (PC1 positive area). The sample points in the group are relatively scattered, but there is no obvious overlap with the samples in group W as a whole, indicating obvious differences in gut microbial community structure between the two groups. These results suggested that the differences in body weight were closely related to the changes in gut microbial community structure, which was consistent with the conclusion that gut microbiota could regulate host growth and development
(Zhang et al., 2022; Yadav and Jha, 2019).
Differential gut microbiota analysis
MetaStat differential species analysis showed that
Caproiciproducens belonging to the family Ruminococcaceae was extremely significantly enriched in the W group (
q<0.01) and was almost absent in the B group (Fig 6).
Caproiciproducens is mainly involved in the synthesis of short-chain fatty acids such as hexanoic acid, which can provide energy for intestinal epithelial cells, improve intestinal barrier function and enhance energy metabolism efficiency, thereby promoting host weight gain (
Esquivel-Elizondo et al., 2021). This indicated that
Caproiciproducens may be a key functional bacterium related to the weight gain of muchuan black-boned chickens, which could be used as a candidate strain for the development of microecological preparations. The results of this study are consistent with the conclusions of many studies on the composition and structure of intestinal microorganisms in livestock and poultry. The enrichment of the rumen cocci family and the related bacterial genera for SCFA synthesis has been confirmed to be positively correlated with growth performance and body weight indicators.
Wang et al., (2023) discovered in their research on local chicken breeds that the microbiota in the cecum can account for approximately 10.1% of the individual body weight variation. Among them, the SCFA-producing bacterial flora positively regulates growth performance through the fatty acid metabolism pathway.
Akram et al., (2024) further discovered that
Ruminococcaceae was enriched in the cecum of high-weight chicken flocks and was significantly correlated with the concentrations of butyric acid and caproic acid as well as the feed conversion efficiency. This study provides a scientific basis for analyzing the microbial mechanism underlying the growth traits of Muchuan Black-Boned Chickens and also offers a candidate target for the development of probiotics for local chicken breeds.