Abstract
Minimizing the utilization of antibiotics in animal production is crucial to prevent the emergence of antimicrobial resistances. Thus, research on alternatives is needed to maintain productivity, sustainability, and animal health. To gain a comprehensive understanding of probiotics' modes of action on performance, intestinal microbiota, and gut health in poultry, 3 probiotic strains (Enterococcus faecalis CV1028 [EntF], Bacteroides fragilis GP1764 [BacF], and Ligilactobacillus salivarius CTC2197 [LacS]) were tested in 2 in vivo trials. Trial 1 comprised of a negative control group fed basal diet (BD) and 3 treatment groups that received BD with EntF, BacF and LacS. Trial 2 included a negative control group, a positive control group with Zinc-Bacitracin as antibiotic growth promoter (AGP), and 2 groups treated with a blend of probiotics (EntF+BacF+LacS) during 0 to 10 or 0 to 35 d, respectively. Wheat-soybean-rye based diets without exogenous enzymes were used as a challenge model to induce intestinal mild- or moderate-inflammatory process in the gut. In Trial 1, individually administered probiotics improved FCR at 8 d compared to Control, but these positive effects were lost in the following growing periods probably due to the high grade of challenging diet and a too low dose of probiotics. In Trial 2, both Probiotic treatments, administered only 10 or 35 d, significantly improved FCR to the same extent as of the Antibiotic group at the end of the trial. Although the performance between antibiotic and probiotic mixture showed similar values, microbiota analysis revealed different microbial composition at 7 d, but not at 21 d. This suggests that modes of action of the AGP and the tested probiotic blend differ on their effects on microbiome, and that the changes observed during the first days' posthatch are relevant on performance at the end of the study. Therefore, the probiotics administration only during the first 10 d posthatch was proven sufficient to induce similar performance improvements to those observed in birds fed antibiotic growth promoters throughout the whole experimental trial.