Regulation effect of Lactobacillus johnsonii on chickens infected with Ascaridia galli

Ascaridia galli, a highly prevalent intestinal parasite of poultry globally, poses significant challenges to prevention and control strategies in poultry industry due to its increasing resistance to anthelmintic. Therefore, this study aims to investigate the regulatory effects of Lactobacillus johnsonii on growth performance and intestinal health of broilers infected with A. galli. In this study, 80 one-day-old broilers were randomly assigned to a 2 × 2 factorial arrangement of treatments, which included two levels of L. johnsonii (0 or 1 × 10⁹ CFU/mL) and two infection statuses (A. galli challenge or no-challenge). The results showed that during the early stage of A. galli infection (3-14 dpi), these general detection indicators demonstrated L. johnsonii has a significant alleviating effect, including lower worm load, improved growth performance, enhanced intestinal barrier function, elevated antioxidant markers (GSH, T-AOC), and increased disaccharidase enzyme activity. Moreover, qRT-PCR analysis revealed the up-regulated expression of barrier genes (ZO-2, OCLN) and nutrient transporters (EAAT3, FATP4), along with the reduced pro-inflammatory (IL-6, IFN-γ) and apoptotic factors (CASP1, CASP9) in the LA (L. johnsoniig + A. galli) group were showing no significant difference compared with the PP group (PBS + PBS). In addition, significantly reduced abundance of L. johnsonii in the LA group resulting in no significant protective efficacy against A. galli infection at 30 dpi. On the other hand, in vitro experiments confirmed the concentration-dependent larvicidal effect of probiotic supernatant, while the probiotic itself did not exhibit direct larvicidal activity. In conclusion, L. johnsonii exhibits potential for a reduction of negative effects of A. galli infection through a dual mechanism, except regulating intestinal homeostasis to exert protective effects, the more important is producing metabolites with potent and rapid larvicidal activity.