In recent years, outbreaks of Seneca Valley virus (SVV) in pig farms have raised concerns about disease resistance in different pig breeds. Min pigs are an excellent local pig breed in China, but the breed’s strong disease resistance mechanism has not been clearly investigated. In this study, Min pigs and Landrace pigs were challenged with SVV, and the differences in pathogenicity between SVV-infected Min and Landrace pigs were evaluated in terms of production performance, survival rate, immune cell activity, pathological changes, viral titer, and cytokine expression. The results show that the mortality rate in Min pigs was significantly lower than that in Landrace pigs without substantial weight loss. The copy number of SVV RNA in the intestinal mucosa of Min pigs was lower than that in Landrace pigs. Additionally, the IgA and IgG titers in Min pigs were higher than those in Landrace pigs. Both the absolute number and percentage of M1 macrophages were elevated in Min pigs relative to Landrace pigs. This study is the first to identify differences in macrophage activity between SVV-infected Min pigs and Landrace pigs. The presented results indicate the potential research value of studying innate immunity differences in disease resistance between pig breeds.

Pathogenic infections caused by intestinal microecological imbalance pose a critical threat to livestock breeding and human health. Multiple probiotic functions of Lacticaseibacillus casei (L. casei), an important probiotic, are modulated by pyrR-mediated pyrimidine metabolism. This study used L. casei isolated from the intestines of Min pigs (a local pig breed from northeastern China) and its pyrR gene knockout mutant (named L. casei ΔpyrR, ΔpyrR) to investigate their antibacterial, anti-inflammatory, and antioxidant capacities. The results showed that the mutant exhibited significantly attenuated effects compared with the wild-type in disrupting pre-formed biofilms, damaging bacterial morphology, and downregulating the expression of related genes (biofilm and flagellar genes) in Staphylococcus aureus (S. aureus) and Salmonella typhimurium (S. typhimurium). The mutant-derived supernatant also exhibited impaired anti-inflammatory effects in S. typhimurium-challenged IPEC-J2 cells: it was less effective at restraining pathogen-induced IL-1β upregulation and boosting the production of host-derived TGF-β and IL-10, accompanied by altered regulation of the host STING signaling pathway. However, existing data cannot fully distinguish whether STING alteration corresponds to suppressed inflammation or impaired immunity. Additionally, pyrimidine metabolism in L. casei suppresses pathogen-induced reactive oxygen species (ROS) accumulation. These findings are consistent with pyrR-mediated pyrimidine synthesis contributing to the probiotic functions of L. casei, providing an experimental basis for optimizing probiotic preparations and substituting antibiotics.