There are few systematic studies on the dietary fiber requirements of broilers in the late feeding stage, and there are not enough data to support this hypothesis. This experiment was conducted to examine the effects of dietary fiber level on growth performance, nutrient digestibility, immune function and intestinal morphology of broilers from day 22 to 42. A total of 480 one-day-old Arbor Acres broilers with half male and half female were randomly allocated into four groups, with eight replicates in each group and fifteen chickens in each replicate. The experimental period was 42 days. All broilers were fed a basal diet from 1 to 21 days. During the 22–42 day period, the four experimental groups were fed diets with soybean hulls as the fiber source, and crude fiber (CF) levels were 2%, 5%, 8% and 11%, respectively. The results showed that during the 29–42 day period, the average daily feed intake (ADFI) of broilers was higher in the 5% CF and 8% CF groups (p < 0.05), and during the 29–35 day period, the average daily gain (ADG) of broilers was higher and the ratio of feed and gain (F/G) of broilers was lower in the 5% CF and 8% CF groups (p < 0.05). The digestibility of crude protein (CP), ether extract (EE), CF, acid detergent fiber (ADF) and neutral detergent fiber (NDF) was higher in broilers of the 8% CF group (p < 0.05). The immunoglobulin A (IgA), immunoglobulin G (IgG) and immunoglobulin M (IgM) content of the plasma of broilers was higher in the 8% CF group (p < 0.05). The villus height (VH) of the duodenum, jejunum and ileum of broilers was higher, and the crypt depth (CD) was lower in the 8% CF group than that in the 2% CF group (p < 0.05). The ratio of VH and CD (V/C) of the duodenum and jejunum of broilers in the 8% CF group was higher than that in the 2% CF group (p < 0.05). The quadratic regression analysis showed that the optimum dietary CF level was 7–9%. In conclusion, under the conditions of this experiment, a diet of 7–9% CF may promote growth performance by improving the nutrient digestibility, immunity and intestinal morphology of broilers from day 22 to 42.

This research investigated the differences and succession patterns of microbes in different ages, the performance of laying hens, and the effect of Fecal Microbiota Transplantation (FMT) on aged laying hens. First, based on the different laying rates and age, we divided the laying hens into four groups: 75-week-old high-yield (OH, laying rate (LR) > 90%), 75-week-old low-yield (OL, LR < 60%), 75-week-old non-laying hens (OZ, LR = 0%) and 35-week-old high-yield (YH, LR > 90%) with 5 replicates in each group and 6 chickens in each replicate. The microbial metabolic patterns between different ages and laying rates were determined using 16S rDNA technology. Then, to verify the results of microbiome research, we utilized FMT technology to transplant the gut microbiota from OH to OZ (OZ_FMT-OH), thereby revealing the connection between gut microbes and production performance. The results showed that high-yielding hens (YH and OH groups) had higher levels of Superoxide dismutase (SOD) and Immunoglobulin A (IgA) compared to OL and OZ groups. The Villus height to Crypt depth ratio(V/C) was significantly higher in the YH group than in 75-week-old hens (P < 0.05). Alpha diversity indicated higher microbial diversity in the YH group compared to older hens (P < 0.05), with YH hens harboring more Megamonas, OH hens more Bacteroides, and OL and OZ groups showing higher levels of harmful bacteria. The villus height, V/C, mucosal layer thickness, cup cell number acetic acid level, and LR in the OZ_FMT-OH group were significantly higher than those in the OZ group (P < 0.05), while the IL-2 level, crypt depth and cecal intestinal wall thickness were significantly lower than those in OZ group (P < 0.05). FMT also changed the morphological structure of grade follicles and small yellow follicles, improved the microbe composition of cecum and increased Bacteroides abundance. In the late laying period, if the intestinal flora cannot maintain the dynamic balance and carry out timely replacement, the production performance may be decreased, and the increase of Bacteroides abundance in the intestinal tract can improve the intestinal health and production performance of laying hens in the late laying period.

The decline in eggshell quality of aged laying hens represents a major economic challenge in poultry production. While a 28 h ahemeral light cycle has been shown to improve eggshell quality, its underlying mechanism remains unclear. This study randomly assigned 260 74-week-old Hy-Line Brown laying hens to two light cycle groups, a normal 24 h cycle group (16L:8D) and a 28 h ahemeral cycle group (16L:12D). Each treatment comprised 130 hens divided into two replicate groups. The trial lasted 16 weeks. We systematically analyzed circadian rhythms of gut microbiota and serum metabolites using 16S rRNA sequencing and untargeted metabolomics. Compared with the 24 h cycle, the 28 h cycle significantly enhanced eggshell thickness by 0.04 mm and 0.02 mm, and eggshell strength by 4.19 N and 4.76 N at 79 and 84 wk, respectively. Mechanistically, the 28 h light cycle remodeled the circadian rhythms of gut microbiota, increasing their richness and diversity, and altered the rhythmic patterns of serum metabolites. We identified nine microbial genera and three hundred seventy metabolites that exhibited opposite rhythmic patterns under the two light cycles. These changes were primarily enriched in pathways related to amino acid, carbohydrate, lipid, and energy metabolism. Correlation analysis further revealed strong associations between key microbes and functional metabolites. Weissella promotes calcium deposition in eggshells through synergistic interactions with calcium chelators such as gluconic acid and threonine acid. Meanwhile, YRC22 and Paludibacter synergistically support membrane formation substances, thereby promoting the proliferation of uterine epithelial cells and eggshell formation. Our findings indicate that the 28 h ahemeral light cycle improved eggshell quality in aged hens by remodeling the circadian rhythms of gut microbiota and metabolites, thereby synergistically enhancing calcium ion absorption and uterine tissue health. This provides a novel theoretical basis and practical direction for improving late-phase egg quality through light management strategies.

Salpingitis in aged laying hens leads to reduced egg production, severely impacting production efficiency. The use of antibiotics poses significant safety risks, necessitating the development of green alternative strategies. This study aimed to investigate the alleviating effects and underlying mechanisms of Lactobacillus agilis on salpingitis in aged laying hens. A 2 × 2 factorial design was employed, in which 192 80-week-old Hy-Line Grey laying hens were randomly allocated into 4 groups with 6 replicates per group and 8 hens per replicate: control group, Lactobacillus agilis group (2 × 10⁸ CFU/hen/day), salpingitis model group (lipopolysaccharide, LPS 3.7 mg/mL + organic chemical reagent, OCR), and salpingitis + Lactobacillus agilis group (2 × 10⁸ CFU/hen/day + LPS 3.7 mg/mL + OCR). The experiment lasted for 8 weeks, and at the end of week 8, salpingitis was induced by cloacal administration of LPS + OCR. The results showed that Lactobacillus agilis significantly alleviated LPS-induced histopathological damage in the oviduct and reduced histopathological scores (P < 0.05). It decreased serum levels of the pro-inflammatory cytokines interleukin‑1β, interleukin‑6 and interleukin‑17A, and increased the levels of the anti-inflammatory cytokine interleukin‑10 and the mucosal antibody secretory immunoglobulin A (P < 0.05). Furthermore, Lactobacillus agilis improved jejunal villus morphology by increasing villus height and the villus height/crypt depth ratio (P < 0.05). It also modulated the cecal microbiota composition, increasing the abundance of beneficial bacteria such as Verrucomicrobiota and Synergistes, while decreasing potentially harmful bacteria such as Fournierella (P < 0.05). In addition, Lactobacillus agilis suppressed the overexpression of genes related to the TLR4/MyD88/NF-κB inflammatory pathway and pyroptosis genes gasdermin E (GSDME) and caspase 1 (CASP1) in oviduct tissue (P < 0.05). Correlation analysis revealed that Verrucomicrobiota and Synergistes were positively correlated with anti-inflammatory cytokines and negatively correlated with oviduct pathological scores, pro-inflammatory cytokines, and genes involved in the TLR4/MyD88/NF-κB pathway and pyroptosis. In conclusion, Lactobacillus agilis alleviates LPS-induced salpingitis by inhibiting the TLR4/MyD88/NF-κB pathway and pyroptosis, thereby regulating inflammatory mediator levels, while concurrently reshaping the cecal microbiota, ultimately alleviating salpingitis and improving intestinal morphology.