IMPACT OF THE GASTROINTESTINAL MICROBIOME AND FERMENTATION METABOLITES ON BROILER PERFORMANCE

Growth, Carcass Traits, Blood Chemistry and Gut Microbiota in Broiler Chickens Fed Diets Enriched With Garden Cress Seed Powder as a Natural Growth Enhancer

This study investigated the effects of garden cress seed powder (GCSP) as a natural growth promoter and antioxidant agent in broiler diets, focusing on growth performance, carcass characteristics, microbial load and blood traits. A total of 210 1-day-old Arbor Acres broiler chicks were assigned to 3 experimental groups in a completely randomized design. Each group consisted of 7 replicates with 10 unsexed chicks per replicate. The dietary treatments included: (A) a basal diet without additives (control); (GCSP 1) a basal diet supplemented with 1 g GCSP/kg diet and (GCSP 2) a basal diet supplemented with 2 g GCSP/kg diet. The results revealed no significant differences in body weight (BW), BW gain (BWG), feed intake (FI) and feed conversion ratio (FCR) between the GCSP-treated groups and the control. However, numerically, the GCSP-supplemented groups exhibited improved BW, BWG and FCR compared to the control. Carcass traits remained largely unaffected, except for dressing percentage, carcass yield, thigh proportion and abdominal fat percentage, where significant differences were observed. Blood biochemical analysis showed a reduction in total protein, albumin and globulin levels in GCSP-fed groups, whereas high-density lipoprotein (HDL) levels increased and low-density lipoprotein (LDL) and very LDL (VLDL) levels decreased, though these changes were not statistically significant. Immunological and antioxidative responses improved, as evidenced by elevated immunoglobulin Y (IgY), immunoglobulin M (IgM) and superoxide dismutase (SOD) levels, alongside reduced malondialdehyde (MDA) levels in the GCSP-fed groups compared to the control. In conclusion, dietary supplementation with GCSP enhanced broiler immunity and antioxidative status, promoting increased IgY, IgM and SOD levels while reducing MDA levels. These findings highlight GCSP as a potential natural additive to improve broiler health and contribute to the production of healthier poultry products for consumers.

Dietary inclusion of raw potato or high-amylose-corn resistant starches fed for different durations: impact on phenotypic responses and indicators of gut health of broiler chickens

BACKGROUND

This 21-day study evaluated the effects of feeding durations of graded levels (RSL) of raw potato starch (RPS) or high amylose corn starch (HCS) on growth performance, energy utilization and intestinal biochemical metrics in broiler chickens. In total, 300 male broiler chicks were randomly assigned to 10 treatments: three RSL (25 and 50 g kg-1 of RPS and 35 g kg-1 of HCS) and three feeding durations (RSD) (21, 14 or 7 days), plus a corn-soybean meal control diet.

RESULTS

There were significant effects (P < 0.05) of RSL on feed conversion ratio (FCR), apparent ileal digestible energy (AIDE) and nitrogen-corrected metabolizable energy (AMEn). Birds fed 25 g kg-1 RPS had greater FCR than those fed 35 g kg-1 HCS. The AIDE and AMEn were greater in birds fed 35 g kg-1 HCS, except AIDE at 50 g kg-1 RPS and control diets. The RSD × RSL interaction was significant (P < 0.05) for jejunal glucagon-like peptide-2 (GLP-2) and RSD for mucin-2 (MUC-2) expression. Birds fed 25 g kg-1 RPS for 21 and 14 days had higher GLP-2 expression than those fed for 7 days. MUC-2 expression was greater for 21 and 14 days of RS feeding than 7 days.

CONCLUSION

The RSL modulated growth performance and nutrient uptake, whereas gene expression was associated with RSD and RSL synergistic effects. © 2025 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Determining the Fecal Microbiome of Healthy Cockatiels (Nymphicus hollandicus) Fed Seeds Versus Formulated Pelleted Diets by Next-Generation DNA Sequencing

Fecal samples were collected from 34 clinically healthy cockatiels (Nymphicus hollandicus), with 15 consuming a commercially available seed diet and 19 on a formulated pelleted diet. Next-generation DNA sequencing was used to analyze the samples, revealing a diverse microbial landscape. A total of 179 bacterial species from 94 genera and 244 fungal species from 156 genera were identified across both diet groups. Although no significant differences in microbial diversity were observed between the 2 groups, distinct microbial compositions were noted. Notably, Corynebacterium kroppenstedtii and Enterococcus durans/faecium were enriched in the pellet-fed group, whereas Lactobacillus oris and a species in the Brevinemataceae family were more abundant in the seed-fed group. In the mycobiome, Aspergillus penicillioides, Meyerozyma sp, and Fusarium sp were enriched in the pelleted diet group, whereas Bulleribasidium oberjochense was more prevalent in the seed diet group. These findings highlight the nuanced effects of diet on the fecal microbiome of cockatiels, providing valuable insights for avian health management and potential probiotic interventions.

Effect of Ascites Syndrome on Diversity of Cecal Microbiota of Broiler Chickens

Ascites syndrome (AS) is a metabolic disease that seriously affects the growth and development of broiler chickens. Intestinal microbiota play a significant role in the growth of broiler chickens. Therefore, further research on the relationship between AS and intestinal microbiota will help to better understand the impact of AS on broiler growth. In this study, 0.2% sodium chloride was added to the drinking water, which induced AS in broiler chickens, and we detected the influence of AS on the growth performance and cecal microbiota of broiler chickens. The results showed that AS significantly reduced the cecal microbial diversity of broiler chickens and affected the cecal microbial composition at the phylum and genus levels (p = 0.05). Further, LEfSe analysis revealed that AS significantly increased the abundance of Bacteroidetes (p = 0.035) while simultaneously reducing the abundance of Actinobacteria (p = 0.031) in the cecum. Additionally, the differential metabolites associated with polycyclic aromatic hydrocarbon degradation were significantly diminished. The findings suggest that AS may further impact the growth rate of broiler chickens by altering cecal microorganisms.

A cross-study analysis of the effect of a dual-strain probiotic applied via the waterline on the growth performance and gut health of broilers under a mild necrotic enteritis challenge

Probiotics offer potential as an approach for the prevention and control of poultry intestinal diseases, but external factors can influence the birds' response. Combining data from multiple trials provides greater confidence around efficacy under varying production conditions. Therefore, this study combined data from three separate trials analyzing the effect of a dual-strain probiotic comprising Lactobacillus acidophilus AG01 and Bifidobacterium animalis subspecies lactis AG02 on broilers during a mild necrotic enteritis (NE) challenge. In each, 1,440 broilers were assigned to floor-pens (40 birds/pen, 12 pens/treatment) in a completely randomized design. Treatments in each trial were a non-challenged control (C); challenged control (10 x dose of Eimeria/bird on d 14 and 1.0 x ∼109 colony forming units (CFU)/bird of C. perfringens on d 16-20; CC); and CC supplemented daily via the waterline with 1 × 109 CFU/bird of probiotic (CC+Probiotic). Birds were fed corn-soybean mealbased diets by phase (starter: 0 to 14, grower: 15 to 28, finisher: 29 to 42 d of age) ad libitum. Growth performance was monitored over 42 d, NE lesion scoring performed on d 21 and 28 in all trials, and, in Trial 3 only, cecal microbiota composition was analyzed on d 28. From d 1 to 42, CC birds exhibited reduced BW, BW gain (BWG), and feed intake (FI) (-9.2 %, -9.5 %, -5.0 %, respectively; P < 0.05), increased FCR and mortality (+8.5 points and 1.3 % points, respectively; P < 0.05) compared to C, and increased NE induction on d 28 (67.8 vs. 9.4 %, P <0.05). Compared to CC, CC+Probiotic birds exhibited increased BW, BWG and FI (d 42: +6.9 %, +7.1 %, +4.0 %; P < 0.05) and reduced FCR, mortality and d 28 NE lesion scores (-0.5 points, -1.4 % points and -57.1 %, respectively; P < 0.05). The composition of the cecal microbiota of CC+Probiotic birds at 28 d of age exhibited higher abundance of butyrogenic bacterial genera in Trial 3, which may have contributed to the beneficial effects of the probiotic. The results demonstrate that the probiotic ameliorated the negative effects of a mild NE-challenge on growth performance and intestinal symptoms over three trials incorporating variation in season and bird breed.

Implication of digestive functions and microbiota in the establishment of muscle glycogen differences between divergent lines for ultimate pH

Both the quality of chicken meat and the quality of chicks are influenced by the level of breast muscle glycogen reserves. In order to study the role of digestive metabolism in establishing this muscular phenotype, we compared two divergent chicken lines for the ultimate pH (pHu) of the breast meat, a proxy for glycogen reserves. Males aged 4 weeks had twice the breast muscle glycogen content in the pHu- line (low pHu) than in the pHu +  line (high pHu). The increase in glycogen reserves (pHu-) was associated with a higher relative weight of the proventriculus and gizzard, as well as better apparent ileal digestibility of nitrogen and calcium. The diversity of the cecal microbiota was comparable, but three bacterial genera (Lachnospira, Lachnospiraceae UCG-010, Caproiciproducens) varied between the lines. The differences observed could lead to down-regulation of carbon fixation in prokaryotes and of the citrate cycle in the pHu + line. RNA-seq analysis of the jejunum, the major site of nutrient absorption, revealed 149 genes differentially expressed (DE) between the lines, including several genes linked to immunity, hormonal response and circadian rhythms that are less expressed in pHu + animals. Others involved in cell migration and proliferation, and more generally tissue morphogenesis, also differed between the lines. Among the DE genes, several co-localized with Quantitative Trait Loci (QTL) controlling pHu and selection signatures identified in the divergent lines, such as the gene coding for ghrelin, a hormone regulating appetite.

Effect of Triticale Grain in Diets on Performance, Development of Gastrointestinal Tract and Microflora in Crop and Ileum of Broiler Chickens

The purpose of the research was to determine the effect of the use of a diet containing 30% triticale grain. In an experiment lasting 28 days, 180 one-day Ross-308 chickens (sex ratio 1:1) with an average initial body weight in treatment of 44.6 g were randomly assigned to 30 metabolic cages/replications, 6 birds in each. To compare the results between treatments, a one-way ANOVA was used with uneven replication numbers. The control group (I) received a standard diet containing maize and soybean meal. In the other treatments, 30% of different cereals were used: II-wheat, III-barley, and IV-triticale. Significant differences in body weight (BW) and feed conversion ratio (FCR) were observed on the 4th day of the life of broiler chickens (p < 0.05). Differences were determined between the control group (90.7 g BW and 1.32 kg of feed/kg BWG in the case of FCR) and birds receiving barley (93.0 g BW and 1.29 kg of feed/kg BWG in the case of FCR), compared to chickens fed diets with a 30% share of wheat grain (86.2 g BW and 1.53 kg feed/kg BWG in the case of FCR) and triticale (86.6 g BW and 1.53 kg feed/kg BWG in the case of FCR). Later, the differences in performance of birds between treatments did not occur (p > 0.05). In the nutrition of broiler chickens, control or 30% of the triticale diet caused a significant reduction (p < 0.01) of the number of Escherichia coli (E. coli) in the crop of broiler chickens (0 log cfu/g), compared to birds obtaining feed with 30% of wheat (1.78 log cfu/g). The diet containing triticale also reduced the number of E. coli (p < 0.05) within the ileum (0.78 log cfu/g) compared to chickens obtaining barley grain in the diet (2.12 log cfu/g). As a result of the use of triticale grain (p < 0.05), the total length of the bird intestines (199.64 cm) was compared to 30% of barley grain (209.76 cm). The increase in the length of the large intestine of broiler chickens in treatments was positively correlated (r = 0.613, p < 0.05) with the number of Lactobacillus sp. in the ileum. Triticale increased the pH in the crop of broilers chickens. The research results indicate that triticale, after longer storage, can be used in amounts of 30% of the diet without significant effect on the performance of broiler chickens, with a reduction in E. coli in crop in comparison with wheat and in ileum with barley.

Repeated inoculation with rumen fluid accelerates the rumen bacterial transition with no benefit on production performance in postpartum Holstein dairy cows

BACKGROUND

The dairy cow's postpartum period is characterized by dramatic physiological changes, therefore imposing severe challenges on the animal for maintaining health and milk output. The dynamics of the ruminal microbiota are also tremendous and may play a crucial role in lactation launch. We aim to investigate the potential benefits of early microbial intervention by fresh rumen microbiota transplantation (RMT) and sterile RMT in postpartum dairy cows. Twelve fistulated peak-lactation dairy cows were selected to be the donors for rumen fluid collection. Thirty postpartum cows were divided into 3 groups as the transplantation receptors respectively receiving 10 L fresh rumen fluid (FR), 10 L sterile rumen fluid (SR), or 10 L saline (CON) during 3 d after calving.

RESULTS

Production performance, plasma indices, plasma lipidome, ruminal microbiome, and liver transcriptome were recorded. After fresh and sterile RMT, we found that the molar proportion of propionic acid was increased on d 7 in the FR and SR groups and the bacterial composition was also significantly changed when compared with the CON group. A similarity analysis showed that the similarities between the CON group and FR or SR group on d 7 were 48.40% or 47.85%, whereas the similarities between microbiota on d 7 and 21 in the FR and SR groups were 68.34% or 66.85%. Dry matter intake and feed efficiency were not affected by treatments. Plasma β-hydroxybutyrate concentration in the FR group was decreased and significantly different lipids mainly included phosphatidylcholine and lysophosphatidylcholine containing polyunsaturated fatty acids. Hepatic transcriptomics analysis indicated acute-phase response pathways were upregulated in the SR group.

CONCLUSIONS

Our study suggests that RMT can shorten the transition process of the ruminal microbiota of postpartum dairy cows with no benefit on dry matter intake or feed efficiency. Inoculation with rumen fluid may not be a useful approach to promote the recovery of postpartum dairy cows.

Effects of microalgae, with or without xylanase supplementation, on serum immunoglobulins, cecal short-chain fatty acids, microbial diversity, and metabolic pathways of broiler chickens

Modern broilers are highly susceptible to environmental and pathogenic threats, leading to gut disorders and poor nutrient utilization if not managed properly. Nutritional programming using several feedstuffs and coproducts to manage gut health has been studied. This study used microalgae as a functional compound and xylanase enzyme in broilers' diets as a strategy to manage gut health. A total of 162 one-day-old unsexed Cobb 500 broiler chicks were randomly assigned to 1 of the 3 dietary treatments: a) corn-soybean meal-based control diet (CON), b) 3% microalgae (MAG), and c) MAG with xylanase enzyme (MAG+XYN). The chicks were reared for 35 days (d) on a floor pen system maintaining standard environment conditions to evaluate the effects of microalgae, with or without xylanase supplementation, on serum immunoglobulins, cecal short-chain fatty acids (SCFA) production, cecal microbial diversity, and metabolic pathways. No significant differences were found for serum immunoglobulin and cecal SCFA among the treatment groups (P > 0.05). Relative microbial abundance at the genus level showed that MAG and MAG+XYN groups had a diverse microbial community on d 3 and d 35. However, no bacterial genus had a significant difference (P > 0.05) in their relative abundance on d 3, but 16 genera showed significant differences (P < 0.05) in their relative abundance among the dietary treatments on d 35. Most of these bacteria were SCFA-producing bacteria. Moreover, MAG and MAG+XYN-fed broilers had better responses than CON groups for metabolic pathways (D-mannose degradation, pectin degradation I and II, β-1-4-mannan degradation, tetrahydrofolate biosynthesis, glutathione biosynthesis, glutathione-peroxide redox reactions, lactate fermentation to propionate, acetate, and hydrogen, etc.) both on d 3 and d 35. The results suggest that using microalgae, with or without xylanase, had no statistical impact on serum immunoglobulins and cecal SCFA production in broilers. However, an improvement in the cecal microbial diversity and metabolic pathways, which are essential indicators of gut health and nutrient utilization, was observed. Most of the improved metabolic pathways were related to fiber utilization and oxidative stress reduction.

Dietary curcumin supplementation enhances growth performance and anti-inflammatory functions by modulating gut microbiota, microbiota-derived metabolites, and expression of inflammation-related genes in broilers

Curcumin (CUR) is a natural polyphenolic substance that has been widely used since ancient times for its multiple beneficial functions. However, whether CUR affects the growth performance of broilers by altering gut microbiota and metabolite and the underlying mechanism are largely unknown. This study was conducted to evaluate the effect of dietary CUR supplementation on growth performance, anti-inflammatory function, intestinal morphology and barrier, cecum microbiota, and metabolite profile of broilers. Sixty-one-day-old male broilers were randomly divided into the control group (CON, fed a control diet) and the CUR group (fed a control diet supplemented with 200 mg/kg CUR) after 2 d of adaptation. Results showed that after feeding to 52-d-old, compared with CON broilers, the CUR broilers showed improved feed utilization efficiency and growth performance. Furthermore, the CUR broilers showed an improved intestinal morphology, which was demonstrated by a lower crypt depth in the jejunum. The 16S rRNA gene sequencing and non-targeted metabonomics (LC-MS/MS) analysis results showed that the cecum microbiota ecology and function were significantly improved, and the abundance of beneficial flora and metabolites were increased, while the harmful bacteria and metabolites were significantly decreased. In addition, RT-qPCR results showed that CUR significantly reduced inflammatory responses, promoted the formation of the mucosal barrier and enhanced digestion, absorption, and transport of lipids and glucose-related gene expression in the intestine. These above findings demonstrated that dietary CUR supplementation improved growth performance, intestinal morphology, and anti-inflammatory functions, mainly by manipulating cecum microbiota and microbiota-derived metabolites, which provides a credible explanation for the growth-promoting effect and anti-inflammatory functions of CUR and aids our understanding of the mechanisms underlying.

Evolutions in Commercial Meat Poultry Breeding

This paper provides a comprehensive overview of the history of commercial poultry breeding, from domestication to the development of science and commercial breeding structures. The development of breeding goals over time, from mainly focusing on production to broad goals, including bird welfare and health, robustness, environmental impact, biological efficiency and reproduction, is detailed. The paper outlines current breeding goals, including traits (e.g., on foot and leg health, contact dermatitis, gait, cardiovascular health, robustness and livability), recording techniques, their genetic basis and how trait these antagonisms, for example, between welfare and production, are managed. Novel areas like genomic selection and gut health research and their current and potential impact on breeding are highlighted. The environmental impact differences of various genotypes are explained. A future outlook shows that balanced, holistic breeding will continue to enable affordable lean animal protein to feed the world, with a focus on the welfare of the birds and a diversity of choice for the various preferences and cultures across the world.

Evidence of host specificity in Lactobacillus johnsonii genomes and its influence on probiotic potential in poultry

To date, the selection of candidate strains for probiotic development in production animals has been largely based upon screens for desired phenotypic traits. However, increasing evidence indicates that the use of host-specific strains may be important, because coevolution with the animal host better prepares a bacterial strain to colonize and succeed in its respective host animal species. This concept was applied to Lactobacillus johnsonii in commercial poultry production because of its previous correlation with enhanced bird performance. Using 204 naturally isolated chicken- and turkey-source L. johnsonii, we demonstrate that there is a strong phylogenetic signal for coevolution with the animal host. These isolates differ phenotypically, even within host source, and these differences can be correlated with certain L. johnsonii phylogenetic clades. In commercial turkey poults, turkey-specific strains with strong in vitro phenotypes performed better early in life than strains lacking those phenotypes. A follow-up performance trial in broiler chickens demonstrated that chicken-specific strains result in better overall bird performance than nonchicken-specific strains. Collectively, this work provides evidence for the impact of host adaptation on a probiotic strain's potential. Furthermore, this top-down approach is useful for screening larger numbers of isolates for probiotic candidates.

Compound probiotics can improve intestinal health by affecting the gut microbiota of broilers

Probiotics, as a widely used additive, have played a unique advantage in replacing antibiotic products. As a result, the probiotic effects on broiler development, intestinal flora, intestinal barrier, and immunity were assessed by this investigation. Four hundred and eighty 1-day-old Arbor Acres broilers were randomly allotted to 4 groups of 5 replicates with 24 broilers each. The control was fed only a basal corn-soybean meal diet. Probiotics I, probiotics II, and probiotics III were fed basal diet and 1, 5, and 10 g/kg compound probiotics (Lactobacillus casei: Lactobacillus acidophilus: Bifidobacterium = 1:1:2), respectively. We found that broilers in the compound probiotic group exhibited better growth performance and carcass characteristics compared with control, especially among probiotics III group. The intestinal barrier-related genes relative expression of Claudin, Occludin, MUC2, and ZO-1 mRNA in the probiotic group increased at 21 and 42 d compared with control, especially among probiotics III group (P < 0.05). The early gut immune-related genes (TLR2, TLR4, IL-1β, and IL-2) mRNA increased compared with control, while the trend at 42 d was completely opposite to that in the earlier stage (P < 0.05). Among them, probiotics III group showed the most significant changes compared to probiotics II group and probiotics I group. Select probiotics III group and control group for 16S rDNA amplicon sequencing analysis. The 16S rDNA amplicon sequencing results demonstrated that probiotics increased the relative abundance of beneficial microbes such as o_Bacteroidales, f_Rikenellaceae, and g_Alistipes and improved the cecum's gut microbiota of 42-day-old broilers. Additionally, adding the probiotics decreased the relative abundance of harmful microbes such as Proteobacteria. PICRUSt2 functional analysis revealed that most proteins were enriched in DNA replication, transcription, and glycolysis processes. Therefore, this study can provide theoretical reference value for probiotics to improve production performance, improve intestinal barrier, immunity, intestinal flora of broilers, and the application of probiotics.

The effect of Escherichia coli ŽP strain with a conjugation-based colicin E7 delivery on growth performance, hematological, biochemical, and histological parameters, gut microbiota, and nonspecific immunity of broilers

The Escherichia coli ŽP strain (ŽP) was constructed based on the known probiotic E. coli strain Nissle 1917. It was genetically modified to carry the colicin E7 synthesis gene encoding DNase on a conjugative plasmid and the colicin E7 immunity gene in the chromosome. The aim of this study was to evaluate the effects of the daily ŽP per oral administration (5 × 10⁸ or 5 × 10¹⁰ CFU per bird) on the growth performance, hematological, biochemical, histological parameters, gut microbiota, and nonspecific immunity of the 4-24 days old broilers. The ŽP administration increased the abundance of genera Bacillus, Butyrivibrio, and Clostridium and did not influence the weight gain of 4-16 days old broilers. The biochemical parameters were within normal ranges for poultry in experimental and control groups. The ŽP administration had no effect on the erythrocyte numbers, hemoglobin and immunoglobulin Y concentrations, but significantly increased the serum lysozyme concentration, leukocyte numbers, and reactive oxygen species production by phagocytes compared with the control group. It did not cause inflammatory changes in intestinal mucosa, Peyer's patches, and spleen. Thus, the ŽP had no detrimental effects on broiler health and could be an efficient probiotic for the broiler colibacillosis prophylaxis.

Metagenomic analysis reveals the microbiome and antibiotic resistance genes in indigenous Chinese yellow-feathered chickens

Yellow-feathered chickens have great nutritional value and are widely and traditionally used in China, on an industrial scale as broilers. The presence of intestinal microbes has been shown to correlate with poultry performance and serves as an essential reservoir of antibiotic resistance genes (ARGs). Antibiotic resistance is a major public health concern. Here, we investigated functional characteristics of the gut microbiome of indigenous Chinese yellow-feathered chickens (the Huiyang Bearded, Xinghua, Huaixiang, Zhongshan Shanlan, Qingyuan Partridge, and Yangshan chickens) through metagenomic sequencing and reconstructed 409 draft genomes, including 60 novel species and 6 novel genera. Furthermore, we assessed the functions of the intestinal microbial communities and examined the ARGs within them. The results showed that the microbial populations of yellow-feathered broilers were primarily dominated by Bacteroidetes and Firmicutes at the phylum level and Bacteroides at the genus level. Furthermore, the Qingyuan Partridge chicken showed a significantly higher abundance of Prevotella than the other five breeds of chicken. Principal coordinates analysis indicated significant differences in the structures of microbial communities and ARGs, based on the binary Jaccard distance, among the six chicken breeds. Moreover, 989 ARGs conferring tetracycline, multidrug, and aminoglycoside resistance were identified, which represented more than 80% of the faecal resistomes; the most abundant gene in the yellow-feathered chickens was tet(Q). In addition, we found the greatest abundance of resistance genes in Xinghua chickens, indicating that Xinghua chickens are highly resistant to antibiotics. Overall, our findings revealed differences in the gut microbial community structure of indigenous Chinese yellow-feathered broiler breeds and the composition and characteristics of ARGs and antibiotic resistance that enabled us to reconstruct the yellow-feathered chicken gut microbial community genomes. The current data significantly improves our knowledge of the gut microbiome and antibiotic resistance of popular broiler breeds in China.