Dietary supplement Lactococcus lactis improved anti-inflammatory responses and intestinal barrier function of weaned pigs

This study evaluated the effects of dietary probiotic <italic>Lactococcus lactis</italic> on growth performance, frequency of diarrhea, immune responses, and intestinal health of weaned pigs. In a randomized complete block design (block = initial body weight), 48 newly weaned pigs were assigned to two dietary treatments (4 pigs/pen; 6 replicates/treatment; 4-week trial): a basal diet based on corn and soybean meal (CON) and CON supplemented with 0.02% <italic>L. lactis</italic> (LL). Growth performance, frequency of diarrhea, systemic immune responses and serum biochemical parameters, intestinal morphology, and ileal gene expression of tight junction proteins and inflammatory cytokines were measured. No differences were found in growth performance and serum biochemical parameters between CON and LL. However, the LL group tended to show lower the frequency of diarrhea during the first two weeks after weaning (<italic>p</italic> = 0.092), hematocrit levels on day 14 (<italic>p</italic> = 0.093), and serum cortisol concentrations on day 7 (<italic>p</italic> = 0.096) than the CON group. The LL decreased concentrations of serum tumor necrosis factor-α (TNF-α) on day 7 (<italic>p</italic> < 0.05), interleukin-6 (IL-6) on days 7 and 14 (<italic>p</italic> < 0.05), transforming growth factor-β1 (TGF-β1) on day 14 (<italic>P</italic> = 0.057), and interleukin-1β (IL-1β) on day 14 (<italic>p</italic> = 0.082) and day 28 (<italic>p</italic> = 0.070) compared with the CON. Pigs fed LL diet had higher villus area and the number of goblet cells in the small intestine (<italic>p</italic> < 0.05) and had a tendency to increase villus height in the duodenum (<italic>p</italic> = 0.084) compared with those fed CON diet. Furthermore, the LL upregulated (p < 0.05) gene expressions of claudin-1, claudin-4, and tight junction protein-1 in the ileum and downregulated (p < 0.05) gene expressions of TNF-α, TGF-β, IL-1β, IL-6, and interleukin-8 compared with the CON. Consequently, the dietary probiotic <italic>L. lactis</italic> tended to alleviate post-weaning diarrhea; this may be correlated with improved anti-inflammatory responses, intestinal morphology, and gut barrier functions of weaned pigs.