Bovine viral diarrhea virus (BVDV) remains a major cause of calf diarrhea with substantial economic impacts on global cattle production. While emerging evidence suggests that the host microbiota may modulate viral infection processes, the specific gut microbial alterations induced by BVDV infection require elucidation. This study investigated gut microbiota composition and functional changes in BVDV-infected cows through 16S rRNA sequencing. Following the epidemiological screening of a large Angus cattle herd using RT-PCR, we identified four persistently infected (PI) animals and four BVDV-negative controls. Fecal analysis revealed Firmicutes and Bacteroidetes as dominant phyla in both groups. A significant increase in the Ruminococcus genus was observed in PI cows (p < 0.05), with LEfSe analysis identifying Paludibacter as a BVDV-associated biomarker. The PI group exhibited reduced alpha diversity (Faith’s PD index, p < 0.05) and elevated histidine metabolism pathway abundance compared to controls (p < 0.05). These findings demonstrate that persistent BVDV infection induces structural and functional modifications in the bovine gut microbiota, particularly through the enrichment of specific bacterial taxa and altered metabolic potential. The results provide new insights into virus–microbiota interactions, establishing a foundation for understanding how BVDV infection may influence host physiology through microbial community changes.

In this experiment, the rumen microbiota of healthy cows, cows with left-displaced abomasum (LDA), and cows after 7 days of LDA treatment (LDA_7) were compared to explore the correlation between LDA and the rumen microbiota and identify early warning markers for LDA. Compared with the healthy group and the LDA_7 group, the LDA group exhibited fewer Operational Taxonomic Units (LDA: 21,361; Healthy: 23,231; LDA_7: 23,956; p < 0.05). The results revealed significant differences in community structure between LDA-affected cows and healthy cows, as well as between treated and untreated LDA-affected cows. Specifically, the relative abundance of Bacteroidota significantly increased and the relative abundance of Firmicutes significantly decreased in LDA-affected cows (p < 0.05). At the genus level, the abundances of UCG_002, UCG_010, and Bacteroidales_BS11_gut_group significantly increased (p < 0.01), whereas those of Trichosporon, Chryseomicrobium, and [Ruminococcus]_gauvreauii_group significantly decreased in LDA-affected cows (p < 0.01). Functional prediction analysis indicated that amino acid biosynthesis and glycerol ester metabolism were significantly downregulated in LDA-affected cows (p < 0.01). After treatment, the abundance of key microbial taxa (UCG_002 and Lachnospira) and metabolic functions normalized to levels similar to healthy cows (p > 0.05). These findings suggest that changes in rumen microbiota richness and diversity could serve as early warning markers for LDA detection.

The replacement of fishmeal with plant protein is a key strategy for sustainable aquaculture, but reduced feed intake and digestive efficiency remain major constraints. This study evaluated the effects of dietary dimethyl-β-propiothetin (DMPT) supplementation on feed intake, digestive function, antioxidant capacity, and intestinal microbiota in narrow-clawed crayfish (Pontastacus leptodactylus) fed an all-plant protein diet. Three isonitrogenous and isolipidic diets were formulated: a plant protein diet (PPD), an animal protein diet (APD), and a PPD supplemented with 0.5% DMPT. After a 4-week feeding trial, results showed that PPD significantly reduced feed intake and digestive enzyme activities compared to APD, whereas DMPT supplementation restored feed intake to a level comparable to APD, maintained growth-related parameters at intermediate levels, and significantly enhanced α-amylase (AMS), lipase (LPS), and trypsin (TPS) activities. Additionally, DMPT markedly improved hepatopancreatic antioxidant capacity, as indicated by increased total antioxidant capacity (T-AOC), glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD) levels, without affecting muscle composition or intestinal morphology. Microbiota analysis revealed that DMPT altered community structure, increased Bacillota abundance, and promoted microbial network stability. Overall, DMPT supplementation effectively mitigates the limitations of plant protein diets and supports the replacement of animal protein in crayfish aquafeeds.

Pontastacus leptodactylus is an aquatic resource endemic to Xinjiang, and its growth performance is closely related to the composition and structure of its intestinal microbiota. This study used male P. leptodactylus, divided into a high-growth-performance (HGP) group and a low-growth-performance (LGP) group based on growth rates, to analyze differences in intestinal microbiota using microbial sequencing technology. Results showed that the number of ASVs unique to the HGP group (7840, accounting for 65.97%) was substantially higher than that in the LGP group (3383, 28.46%). ALDEx2 analysis identified six ASVs significantly enriched in the LGP group, assigned to Methylobacterium, Devosia, order Rhizobiales, Renibacterium, Stenotrophomonas, and class Mollicutes, which were near-absent in the HGP group. At the phylum level, TM7 was differentially abundant with higher relative abundance in HGP. At the genus level, ten genera showed significant differences: Pseudomonas, Hydrogenophaga, Mesorhizobium, Reyranella, Mycobacterium, Flavobacterium, Ralstonia, Bradyrhizobium, and Aeromicrobium were enriched in HGP, whereas the opportunistic pathogen Plesiomonas was depleted. Alpha diversity analysis revealed significantly higher Chao1, observed species, Shannon, and Faith’s pd indices in the HGP group (p < 0.05). Beta diversity analysis confirmed significant separation in microbial community structure between the two groups (adonis p = 0.018). KEGG pathway analysis showed upward trends in retinol metabolism, shigellosis, geraniol degradation, and xenobiotics metabolism pathways in HGP (p < 0.10), and a significant upregulation of coumarin biosynthesis (p < 0.01). COG analysis revealed eight downregulated functional genes in HGP (p < 0.01), suggesting more complex host–microbiota interactions. This study identifies distinct intestinal microbial signatures associated with growth performance in P. leptodactylus, providing candidate targets for probiotic development and aquaculture management, while causal verification remains the critical next step.

To prevent the spread of antibiotic resistance, bacteriophages have gradually become the most promising alternative to antibiotics for treating bacterial infectious diseases. In this study, using E. coli DC1 as the host strain, we isolated a bacteriophage named Escherichia coli phage XJA18 from farm sewage. We conducted morphological identification, host range determination, biological characteristic analysis, genomic feature analysis, and evaluation of in vitro and in vivo antibacterial effects. Electron microscopy revealed that phage XJA18 belongs to the class Caudoviricetes, with an icosahedral head and a non-contractile long tail. Whole-genome sequencing revealed that the phage has dsDNA with a length of 50,572 bp, with a GC content of 45.33%. The genome does not contain any antibiotic resistance genes or virulence genes, indicating good safety. XJA18 showed lytic activity against 24% of clinically isolated E. coli strains. The optimal multiplicity of infection (MOI) was 0.001, with a latent period of 10 min, a burst period of 30 min, and a burst size of 2.22 × 10² PFU/cell. It remained stable at 4–50 °C and pH 4–12. In vitro antibacterial results revealed that XJA18 had the most pronounced initial bacterial growth suppression at MOI = 0.001 during the first 4 h. In vivo experiments demonstrated that both prophylactic and therapeutic administration of XJA18 could protect against E. coli infection, significantly reducing inflammatory cytokine levels and bacterial loads in the livers and spleens of mice (p < 0.001), significantly increasing body weight (p < 0.05), and reducing histopathological damage to the colon, liver, and lungs. In summary, phage XJA18 can effectively inhibit E. coli and is safe and stable. These characteristics indicate that phage XJA18 has great potential as a novel biological agent to replace antibiotics for treating bacterial infectious diarrhea in calves.