Search Results (122)

Background: The current study aimed to evaluate the effects of the supplementation of protease sources on growth and carcass response, gut health, nutrient digestibility, and cecal microbiota profiles in broilers fed poultry-by-product-meal (PBM)-containing diets. Methods: In total, 800 one-day-old mixed-sex broilers (Arbor Acres) were weighed and allocated to one of the four dietary treatments in a completely randomized design, with eight replicates and 25 birds each per replicate. The treatments were as follows: (1) T₀, control diet (without protease supplementation and 3% PBM); (2) T₁, control diet supplemented with acidic protease at 100 g/ton (50,000 U/g); (3) T₂, control diet supplemented with alkaline protease at 200 g/ton (25,000 U/g); (4) T₃, control diet supplemented with neutral protease at 200 g/ton (25,000 U/g). Results: Protease supplementation enhanced (p < 0.05) body weight gain and the feed conversion ratio, predominantly in broilers fed PBM-based diets containing alkaline protease. Alkaline protease supplementation increased (p < 0.05) the apparent ileal digestibility of proteins (AIDP) by 4.3% and the apparent ileal digestibility of amino acids (AIDAA) by up to 5.8%, except for ornithine. Increments (p < 0.05) in carcass, breast, and leg quarter yields due to protease supplementation were evident, particularly in broilers fed diets containing alkaline protease. Alkaline protease improved (p < 0.05) the duodenal villus height (VH), reduced the crypt depth (CD), and increased the villus height to crypt depth ratio (VCR). Alkaline protease supplementation reduced (p < 0.05) cecal counts of Salmonella, Escherichia coli, and Clostridium in the broilers, whereas it increased (p < 0.05) the Lactobacillus counts. Conclusions: the supplemented alkaline protease resulted in improved growth performance and carcass traits, better gut health, as well as improved ileal digestibility of nutrients, including crude protein (CP) and acid insoluble ash (AIA), with a more balanced cecal microbial composition in broilers. Full article

This study aimed to comprehensively investigate the impact of soybean β-conglycinin on broiler growth performance, nutrient utilization, allergic and inflammatory responses, intestinal barrier integrity, and cecal microbiota. A total of 168 newly hatched (1-day-old) Arbor Acres broilers with similar body weights were randomly divided into 6 treatment groups with 4 replicates of 7 broilers per replicate: the control group received a soybean-free basal diet, while the remaining five experimental groups were provided with diets supplemented with purified soybean β-conglycinin at the doses of 1%, 2%, 3%, 4%, and 5%. The results demonstrated that dietary 1–5% β-conglycinin supplementation significantly reduced the growth performance, nutrient utilization, and content of digestive enzymes in broilers (p < 0.05). Dietary 1–5% β-conglycinin supplementation also significantly increased the serum levels of histamine, β-conglycinin-specific IgY and IgM, TNF-α, and IL-6 and decreased IL-10 levels; the 3% group had the highest levels of histamine, TNF-α, and IL-6 and the lowest levels of IL-10 (p < 0.05). β-conglycinin supplementation significantly down-regulated the mRNA expression of tight junction proteins, MUC2 and IL-10, and up-regulated the expression of TNF-α and IL-6 in the small intestinal mucosa (p < 0.05). Furthermore, the Shannon and Simpson indices were significantly reduced by dietary 1–5% β-conglycinin administration (p < 0.05). The relative abundance of beneficial bacteria (Blautia, Lactobacillus, and Butyricoccus) was significantly decreased in all treatments (p < 0.05). Taken together, these findings suggest that β-conglycinin induces allergic and inflammatory responses, impairs intestinal barrier integrity, and alters the intestinal microbial balance, ultimately leading to reduced nutrient utilization and inhibited growth in broilers. Notably, our study demonstrated that dietary supplementation with 1% β-conglycinin already had various negative effects on broilers, and particularly supplemental 3% β-conglycinin induced serious allergic and inflammatory reactions. Therefore, in the present study, it is recommended that the inclusion level of β-conglycinin in broiler formula feed should not exceed 1%, i.e., the β-conglycinin content in the diet should not exceed 0.6% (converted from β-conglycinin purification purity). Full article

Studies demonstrated that Bacillus coagulans (B. coagulans) as a dietary additive enhanced broiler growth performance, yet its mechanisms of action modulation remained unclear. Therefore, this study investigated effects of dietary B. coagulans BCH0 (1 × 10⁹ CFU/kg) on growth performance, intestinal morphology, gut microbiota, and ileal transcriptomics in Arbor Acres broilers using a completely randomized design. A total of 200 one-day-old broilers were allocated to control (Con, basal diet) and experimental (BCH0, basal diet + 1 × 10⁹ CFU/kg B. coagulans BCH0) groups (10 replicates/group, 10 birds/replicate) over a 42-day trial. The results revealed that BCH0 significantly increased body weights (BW) at 21 and 42 days (p < 0.05), improved the average daily gain (ADG) during the starter (1–21 days) and overall phases (1–42 days), and reduced the ratio of feed intake to body weight gain (F/G) across all phases (p < 0.05). Duodenal morphology analysis indicated a BCH0 elevated villus height (+16.9%, p < 0.01) and villus height/crypt depth (V/C) (p < 0.01) and no significant differences in crypt depth (p = 0.46). In the ileum, the BCH0 group exhibited a significantly greater villus height (p < 0.01), crypt depth (p < 0.05), and V/C (p < 0.05) than the Con group. Microbiota analysis revealed no significant differences in α-diversity or β-diversity, but phylum-level shifts involved an increase in Firmicutes and a reduction in Actinobacteriota in the BCH0 group. At the genus level, dominance shifted from Romboutsia (Control group) to Lactobacillus (BCH0 group), accompanied by marked reductions in Turicibacter, Ldatus_arthromitus, and Rothia. Ileal transcriptomics identified 605 differentially expressed genes, with KEGG enrichment highlighting activated nutrient assimilation pathways (p < 0.05), including carbohydrate, mineral, fat, and protein digestion/absorption. These findings collectively demonstrated that B. coagulans BCH0 enhanced broiler growth through the synergistic modulation of beneficial microbiota, the upregulation of nutrient metabolism genes, and intestinal architectural optimization, supporting its role as a sustainable microbial additive for enhancing poultry productivity and gut health. Full article

This study aimed to investigate the effects of supplementing broiler feed with high-yield protease Bacillus subtilis strain FRE76 on growth performance, slaughter performance, apparent digestibility, intestinal morphology, and intestinal microbiota. One-day-old Arbor Acres broilers (n = 240) were randomly assigned to four groups (n = 6 replicates; 10 animals per replicate), in which their basal diet was supplemented with B. subtilis strain FRE76 at 0 CFU/kg (group C), 3.60 × 10⁸ CFU/kg (group L), 1.08 × 10⁹ CFU/kg (group M), and 1.80 × 10⁹ CFU/kg (group H). The experiment lasted for 42 d and comprised two phases: Days 1–21 and days 22–42. The broilers’ body weight at 21 d and the average daily gain at 1–21 d in the L and H groups increased significantly relative to those in group C (p < 0.05). The half-bore weight, half-bore percentage, and breast muscle percentage in group L were significantly higher (p < 0.05) than those in group C. The apparent digestibility of crude protein in group L and the ether extract in groups L, M, and H were significantly increased at 22–42 d compared with those in group C (p < 0.05). In group L, the jejunal villus height and villus height/crypt depth increased significantly relative to those in group C (p < 0.05). The chymotrypsin and trypsin activities tended to increase in the B. subtilis FRE76 groups (p = 0.072 and p = 0.056, respectively) relative to those in group C. Additionally, the abundance of Bacteroidota, Proteobacteria, Alistipes, Clostridia_vadinBB60_group, and Parabacteroides increased significantly in the B. subtilis FRE76 groups (p < 0.05). In conclusion, dietary B. subtilis FRE76 could improve broilers’ body weight, average daily gain, apparent digestibility, protease activity, intestinal morphology, and gut microbiota. Full article

The current experiment aimed to investigate the effects of sodium butyrate (SB) and vitamin D3 (VD3) supplementation on the growth performance, immune status, antioxidant capacity, and gut health of young broilers under cold stress. A total of 144 1-day-old Arbor Acres chicks were randomly allotted to three treatments with 6 replicates of 8 birds: (1) basal diet; (2) basal diet + cold stress; and (3) basal diet with 1 g/kg SB and 2000 IU/kg VD3 + cold stress. Birds were exposed to cold stress at 16 ± 1 °C for 72 h (d 18–21) and 26 ± 1 °C for the control. The results indicated that the SB/VD3 diet could alleviate the reduction in average daily gain (ADG) caused by cold stress (p < 0.05). The SB/VD3 diet decreased the serum endotoxin level and ileal interleukin-1β gene expression and upregulated interleukin-10 and nuclear factor erythroid 2-related factor 2 (Nrf2) gene expression compared with cold-stressed birds (p < 0.05). Furthermore, cold stress altered the composition of gut microbiota, including a decrease in Clostridium_sensu_stricto_1, whereas the SB/VD3 diet prevented the reduction. In conclusion, the SB/VD3 diet mitigated the negative effects of cold stress on growth performance and the intestines by strengthening intestinal barrier function and stabilizing gut microbiota balance in broiler chicks, and these results can help to manage cold stress. Full article

Broilers grown in a high-density (HD) stocking environment may experience intense competition that may adversely affect their growth relative to animals reared at a normal density (ND). The growth performance of HD broilers is increased by aspirin eugenol ester (AEE), although the mechanism by which this compound modulates hypothalamus-regulated feeding behavior is unclear. The aims of this study were to determine the effects of including AEE in the basal diet on the hypothalamic transcriptome and to examine in parallel the impact of these modifications on broiler production performance in HD conditions. Three hundred sixty one-day-old male Arbor Acres broilers were randomly divided into four groups: an ND group (14 broilers/m²), HD group (22 broilers/m²), ND-AEE group, and HD-AEE group. Each treatment group had 10 replicates, with 7 broilers per replicate in the ND and ND-AEE groups and 11 broilers per replicate in the HD and HD-AEE groups. Broiler growth performance was monitored, and hypothalamus samples were collected for transcriptome analysis on day 28. The HD group exhibited a reduced body weight (p < 0.01) at this timepoint compared to the ND group. However, the addition of AEE significantly improved average daily feed intake, average daily gain, and feed conversion ratio in the HD group from days 22 to 28 compared to the HD group without AEE (p < 0.05). The transcriptome results showed that 20 signaling pathways were commonly enriched among the groups (ND vs. HD, HD vs. HD-AEE). Several potential candidate genes were identified as involved in chicken central nervous system development and regulation of feed intake. Thus, the current study provides new insights into hypothalamic transcription patterns that are associated with the ameliorative effects of AEE in HD broilers. Full article

Bone metabolism dynamic balance is pivotal to bone formation in broilers. Long photoperiods have resulted in leg bones disorders in broilers. Melatonin (MT) is an essential hormone that protects the growth and development of bones, but the functions of melatonin on leg bone metabolism are poorly defined in long photoperiod broilers. A total of 216 healthy 5-day-old Arbor Acres (AA) male broiler chickens were randomly allocated into three treatment groups, i.e., 12L:12D photoperiod, 18L:6D photoperiod, 18L:6D photoperiod with exogenous MT supplementation (18L:6D + MT) for 2 weeks. Here, we found that 18L:6D photoperiod increased tibial length (p < 0.001), circumference (p = 0.012) and long diameter (p = 0.003) of broilers, but decreased the tibial weight index (p = 0.038) and strength. The 18L:6D photoperiod induced the tibial cartilage damage, decreased the osteoblast/osteoclast ratio (p = 0.002) and decreased the medullary cavity collagen fiber (p = 0.018) in broilers. Exogenous MT improved the tibial strength, relieved the tibial cartilage damage, increased the tibia osteoblast activity, alleviated osteoclast recruitment and activation and enhanced the collagen fiber in medullary cavity in long photoperiod broilers. Taken together, exogenous MT improved the tibial performance, morphology and formation of broilers underlying long photoperiod. Full article

Salmonellosis in broilers is a disease with considerable economic implications for the poultry industry. As a foodborne illness, it also poses a public health risk due to potential cross-contamination. Probiotics have been proposed as alternative feed additives aiming to enhance growth, livestock productivity, and overall health. This study investigated the dietary impact of Lactococcus lactis JNU 534 on growth performance, blood characteristics, internal organ weight, and meat quality in broilers inoculated with Salmonella enteritidis (SE). A total of 96 one-day-old Arbor Acres broiler chickens, comprising both sexes, were challenged with SE and randomly assigned into two treatment groups and housed in eight pens (four pens per each treatment, with 12 birds per pen). They were fed a commercial broiler diet for 35 days. The two dietary treatment groups consisted of a control group receiving commercial feed, and a treatment group receiving commercial feed supplemented with 0.3% L. lactis JNU 534. Probiotic supplementation significantly improved average body weight gain, feed efficiency, and carcass yield compared to the control group (p < 0.05). Notably, the abdominal fat pad was significantly reduced in the probiotics group (p < 0.05). Meat quality assessments revealed no significant differences between the groups in terms of meat pH, cooking loss, drip loss, and water-holding capacity. These findings suggest that L. lactis JNU 534 is a promising candidate to mitigate the negative effects of Salmonella on growth performance in commercial broiler farms, without adversely affecting health. Extending the research to other types of livestock could help confirm its wider use as an alternative to antibiotics. Full article

As animal welfare becomes more active in livestock industry, research is being conducted on ways to improve poor housing environments, reduce stress, and meet welfare standards. Among these, environmental enrichment methods are effective in reducing stress and creating a welfare-friendly rearing environment, but there are few cases of actual application to farms. Therefore, we aimed to investigate the effect of providing pecking materials (grain blocks), known as one of the environmental enrichment methods, to commercial broiler farms. This study used two facilities that could accommodate 32,000 one-day-old broilers (Arbor acres) per building, and two groups (control and treatment groups) were designed after creating two identical areas within each building (total two treatments, two replicates, 16,000 birds per replicate). Two identical zones within the house were created by installing a partition in the center; one side was provided with grain blocks (one grain block per 1000 birds), and the other side was not. Analysis items included productivity (body weight, uniformity), environmental variables (litter and air), welfare indicators (leg, gait score, feather cleanliness score), and serum corticosterone levels. Analysis of all items was conducted twice, on the 19th and 27th, taking into account the farm’s feed change date and slaughter schedule. Other environmental conditions (density, lighting, ventilation, temperature, humidity, feed, and water) were the same. As a result, no difference in productivity was observed according to enrichment, and the quality of litter and air was similar. Also, there was no significant difference in welfare indicators. Interestingly, however, provision of the environment enrichment lowered serum corticosterone levels (p < 0.05). The implications of our study are that grain blocks as a pecking material are an effective way to reduce stress without adversely affecting broiler performance and rearing environment. However, it is still necessary to explore optimal enrichment materials that can help not only the welfare level but also the broiler performance. Full article

Intestinal health is vital for poultry production, and protein plays a key role in intestinal nutrition. The present study used 16S rRNA gene sequencing and serum metabolomics to investigate the effect of CAP on the cecal microflora structure and serum metabolites in 42-day-old broiler chickens. A total of 480 one-day-old Arbor Acres broiler chickens were randomly divided into four treatments with twelve replicates comprising 10 chickens each, evenly divided by sex. The four groups were basal diet group (CAP0), treatment group 1 (CAP2), treatment group 2 (CAP3), and treatment group 3 (CAP4). The broilers in the CAP0 group were fed a basal diet (without CAP), while those in the CAP2, CAP3, and CAP4 groups received diets containing 2%, 3%, and 4% CAP, respectively. Growth performance results showed that dietary CAP supplementation significantly ameliorated the feed conversion rate (FCR) of broilers at 42 days in the CAP3 and CAP4 groups (p < 0.05). Microbial results revealed that CAP did not alter the dominant microorganisms in the cecum at the phylum, family, and genus levels. LEfSe analysis showed significantly higher relative abundances of p_Desulfobacterota, f_Desulfovibrionaceae, and g_Ruminococcus in the CAP3 group compared to the CAP0 and CAP4 groups. Metabolomic analyses indicated that the effect of incorporating CAP into the diet on serum metabolites primarily focused on organic acids and their derivatives, small peptides, amino acid derivatives, and oxidized lipids. The addition of 3% or 4% CAP to the diet can enhance metabolic pathways such as the citrate cycle (TCA cycle) and arginine and proline metabolism. In summary, incorporating CAP into the diet can increase the relative abundance of beneficial bacteria in the cecum and improve the feed conversion efficiency of broilers by enhancing amino acid and energy metabolism. Full article

Accurate prediction of amino acid requirements in fast-growing broilers is crucial for cost-effective diet formulation and reducing nitrogen excretion to mitigate environmental impact. This study developed a dynamic model to predict standardized ileal digestible amino acid requirements throughout broiler growth using a factorial approach and the comparative slaughter technique, considering maintenance, growth, and gender factors. The model was based on an experiment were designed using 480 15-day-old Arbor Acres chickens randomly assigned to 10 groups. A linear equation was derived using established growth and protein deposition curves to calculate maintenance and growth coefficients. Models for five essential amino acids under different amino-acid-to-protein ratios were created (R² > 0.70). The model effectively estimated daily amino acid needs and specific time intervals. Comparisons with NRC (1994), BTPS (2011), and Arbor Acres manual (2018) showed higher predicted requirements for lysine, methionine, valine, and threonine than Arbor Acres (2018) and BTPS (2011), significantly exceeding NRC (1994). Arginine predictions aligned with BTPS in early stages, but were slightly lower in later stages. This supports the further development of dynamic amino acid models. Full article

This study aimed to evaluate the effects of Mosla chinensis extract (MCE) on broiler intestinal health. A total of 240 1-day-old Arbor Acres (AA) broilers (balanced for sex) were randomly allocated into four treatment groups, each with six replicates of 10 chickens. The study comprised a starter phase (days 1–21) and a grower phase (days 22–42). The control group (C) received a basal diet, while the experimental groups were supplemented with low (S1, 500 mg/kg), medium (S2, 1000 mg/kg), and high doses (S3, 2000 mg/kg) of MCE. The results showed that MCE supplementation significantly improved average daily gain in broilers (p < 0.05) and reduced the feed-to-gain ratio in broilers. Additionally, MCE enhanced the anti-inflammatory and antioxidant capacity of broilers. In the duodenum and cecum, MCE significantly upregulated the expression of tight junction proteins Claudin-1, and Occludin, with the high-dose group showing the strongest effect on intestinal barrier protection (p < 0.05). There was no significant difference in ZO-1 in dudenum (p > 0.05). Microbial analysis indicated that MCE supplementation significantly reduced the Chao and Sobs indices in both the small and large intestines (p < 0.05). At the same time, the Coverage index of the small intestine increased, with the high-dose group demonstrating the most pronounced effect. Beta diversity analysis revealed that MCE had a significant modulatory effect on the microbial composition in the large intestine (p < 0.05), with a comparatively smaller impact on the small intestine. Furthermore, MCE supplementation significantly increased the relative abundance of Ruminococcaceae and Alistipes in the large intestine, along with beneficial genera that promote short-chain fatty acid (SCFA) production, thus optimizing the gut microecological environment. Correlation analysis of SCFAs further confirmed a significant association between the enriched microbiota and the production of acetate, propionate, and butyrate (p < 0.05). In conclusion, dietary supplementation with MCE promotes healthy growth and feed intake in broilers and exhibits anti-inflammatory and antioxidant effects. By optimizing gut microbiota composition, enhancing intestinal barrier function, and promoting SCFA production, MCE effectively maintains gut microecological balance, supporting broiler intestinal health. Full article

This article aims to investigate the mechanism by which Bacillus amyloliquefaciens alleviates lipopolysaccharide (LPS)-induced intestinal oxidative stress. The study involved two experimental subjects: human colorectal adenocarcinoma (Caco-2) cells and Arbor Acres broiler chickens. The experiment involving two samples was designed with the same treatment groups, specifically the control (CK) group, lipopolysaccharide (LPS) group, Bacillus amyloliquefaciens (JF) group, and JF+LPS group. In the Caco-2 experiment, we administered 2 μg/mL of LPS and 1 × 10⁶ CFU/mL of JF to the LPS and JF groups, respectively. In the broiler experiment, the LPS group (19–21 d) received an abdominal injection of 0.5 mg/kg BW of LPS, whereas the JF group was fed 1 × 10⁷ CFU/g of JF throughout the entire duration of the experiment (1–21 d). The results indicated the following: (1) JF significantly decreased the DPPH free radical clearance rate and hydrogen peroxide levels (p < 0.05). (2) JF significantly enhanced the total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and glutathione peroxidase (GSH Px) activity in Caco-2 cells (p < 0.05), while concurrently reducing malondialdehyde (MDA) content (p < 0.05). (3) Compared to the CK group, JF significantly increased the mRNA expression levels of nuclear factor-erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), SOD, catalase (CAT), GSH-Px, interleukin-4 (IL-4), interleukin-10 (IL-10), Claudin, Occludin1, zonula occludens-1 (ZO-1), and mucin 2 (MUC2) in Caco-2 cells (p < 0.05), while concurrently reducing the mRNA expression of Kelch-like ECH-associated protein 1 (Keap1), tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), and interleukin-8 (IL-8) (p < 0.05). In comparison to the LPS group, the JF+LPS group demonstrated a significant increase in the mRNA expression of Nrf2, SOD, GSH-Px, and IL-4, as well as Occludin1, ZO-1, and MUC2 in Caco-2 cells (p < 0.05), alongside a decrease in the mRNA expression of Keap1, TNF-α, and IL-1β (p < 0.05). (4) In broiler chickens, the JF group significantly elevated the levels of T-AOC, CAT, and GSH-Px in the jejunum while reducing MDA content (p < 0.05). Furthermore, the CAT level in the JF+LPS group was significantly higher than that observed in the LPS group, and the levels of MDA, TNF-α, and IL-1β were significantly decreased (p < 0.05). (5) In comparison to the CK group, the JF group exhibited a significant increase in Nrf2 levels in the jejunum of broiler chickens (p < 0.05). Notably, the mRNA expression levels of IL-4, IL-10, Claudin, Occludin1, ZO-1, and MUC2 were reduced (p < 0.05), while the mRNA expression levels of Keap1, TNF-α, and IL-1β also showed a decrease (p < 0.05). Furthermore, the mRNA expression levels of Nrf2, Occludin1, ZO-1, and MUC2 in the JF+LPS group were significantly elevated compared to those in the LPS group (p < 0.05), whereas the mRNA expression levels of Keap1 and TNF-α were significantly diminished (p < 0.05). In summary, JF can enhance the intestinal oxidative stress response, improve antioxidant capacity and intestinal barrier function, and decrease the expression of inflammatory factors by regulating the Keap1/Nrf2 signaling pathway. Full article

Skeletal muscle fiber characteristics are pivotal in assessing meat quality. However, there is currently a lack of research precisely quantifying the total number of myofibers (TNM) of skeletal muscles. This study used Arbor Acres (AA) broilers and Wenchang (WC) chickens to determine the TNM of several skeletal muscles and the meat quality of the pectoralis major muscle (PM). The results showed that the TNMs of the PM in AA males and females were 935,363.64 ± 92,529.28 and 873,983.72 ± 84,511.28, respectively, significantly higher than those in WC (511,468.97 ± 73,460.81 and 475,371.93 ± 70,187.83) at 7 days of age (p < 0.01). In terms of gastrocnemius medialis in AA males and females, we recorded values of 207,551.43 ± 31,639.97 and 177,203.23 ± 28,764.01, showing a significant difference compared to the values observed in WC (146,313.03 ± 29,633.21 and 124,238.9 ± 20,136.95) (p < 0.01). Similarly, the levels of gastrocnemius lateralis exhibited a significant difference between AA and WC (p < 0.01). Furthermore, the essential, umami, and sweet amino acids were found to be significantly higher in WC compared to AA (p < 0.01). These findings offer valuable data and insights for accurately quantifying the TNM in livestock and for the development of further genetic breeding strategies for meat quality. Full article

This study investigated whether variations in growth response to low nutrient density across breeds are linked to microbiota regulation. Arbor Acres (AA) and Beijing-You (BY) were fed high- (HN) and low-nutrient (LN) diets from day (d) 0 to d42. Body weight, feed intake, and intestinal measurements were recorded, and microbiota from the ileum and cecum were analyzed on d7, d21, and d42. Results showed that AA broilers had greater growth performance with a lower feed conversion ratio (FCR) and greater average daily gain (ADG) than BY chickens. The LN diet negatively affected AA broiler growth due to impaired intestinal development, while BY chickens compensated by increasing feed intake. Microbiota composition was primarily affected by breed than by nutrient density, with AA broilers having more beneficial bacteria and BY chickens having more short-chain fatty acid (SCFA)-producing bacteria. The LN diets reduced anti-inflammatory bacteria such as Shuttleworthia and Eisenbergiella in the cecum on d7. By d21, LN diets decreased Lactobacillus and increased proinflammatory Marvinbryantia, potentially impairing growth. However, LN diets enriched SCFA-producing bacteria like Ruminococcaceae_UCG.013, Eisenbergiella, and Tyzzerella in BY chickens and Faecalitalea in AA broilers by d21, which may benefit gut health. By d42, LN diets reduced genera linked to intestinal permeability and fat deposition, including Ruminococcus_torques_group, Romboutsia, Erysipelatoclostridium, and Oscillibacter. Additionally, LN diets enriched Christensenellaceae_R-7_group in AA broilers, associated with intestinal barrier integrity, and increased anti-inflammatory bacteria Alistipes and Barnesiella in AA broilers and BY chickens, respectively, by d42. Overall, AA broilers were more susceptible to reduced nutrient density due to impaired intestinal development, while BY chickens adapted better by increasing feed intake. The microbiota responses to low nutrient density varied over time, potentially negatively affecting gut health in the early stage and growth in the middle stage but possibly improving lipid deposition and gut health in the middle and late stages. Full article