This study aimed to understand the changes in the milk and gut microbiota of dairy cows with mastitis, and to further explore the relationship between mastitis and the microbiota. In this study, we extracted microbial DNA from healthy and mastitis cows and performed high-throughput sequencing using the Illumina NovaSeq sequencing platform. OTU clustering was performed to analyze complexity, multi-sample comparisons, differences in community structure between groups, and differential analysis of species composition and abundance. The results showed that there were differences in microbial diversity and community composition in the milk and feces of normal and mastitis cows, where the diversity of microbiota decreased and species abundance increased in the mastitis group. There was a significant difference in the flora composition of the two groups of samples (P < 0.05), especially at the genus level, the difference in the milk samples was Sphingomonas (P < 0.05) and Stenotrophomonas (P < 0.05), the differences in stool samples were Alistipes (P < 0.05), Flavonifractor (P < 0.05), Agathobacter (P < 0.05) and Pygmaiobacter (P < 0.05). In conclusion, the microbiota of the udder and intestinal tissues of dairy cows suffering from mastitis will change significantly. This suggests that the development of mastitis is related to the endogenous pathway of microbial intestinal mammary glands, but the mechanisms involved need further study.

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) continues to pose a substantial threat to the global swine industry, with recombination-driven evolution generating novel variants that complicate disease control. In this study, two novel recombinant PRRSV-2 strains, designated GXNN202004a and GXGG20210301, were isolated from PRRS-affected pig farms in southern China. Whole-genome sequencing and phylogenetic analysis revealed that both strains possess an NADC30-like backbone, with GXNN202004a arising from recombination between NADC30 and JXA1 and GXGG20210301 representing a multi-lineage recombinant derived from NADC30, JXA1, and QYYZ. Genomic characterization identified a characteristic discontinuous 131-amino-acid deletion (111+1+19 aa) in the NSP2 coding region, along with a previously unreported six-amino-acid deletion in GXGG20210301. Animal pathogenicity assays demonstrated that both strains induced moderate clinical signs, including persistent fever, respiratory symptoms, and growth impairment, without causing mortality in piglets. Viral loads were detectable in multiple tissues, serum, and nasal swabs, indicating broad organ tropism and shedding potential. These findings enrich the molecular epidemiological data on PRRSV in China, highlight the increasing genetic diversity and recombination complexity of circulating strains, and provide scientific evidence for improved PRRS surveillance and vaccine development strategies in southern China.