Efficacy of Probiotic Lactobacillus spp. Isolated From Healthy Korean Indigenous Calves

Background: A healthy gut microbiota enhances immune function and reduces infection susceptibility in neonatal calves. Objectives: This study evaluated the probiotic efficacy of Lactobacillus amylovorus, Lactobacillus reuteri and Lactobacillus johnsonii isolated from Korean indigenous calves in improving gut microbiota, inhibiting pathogen colonization and enhancing immunity in newborn calves. Methods: These strains were fed orally at 10⁹ colony-forming unit (CFU)/g in a mixture, five times every 2 days. Experiment 1 targeted calves under 10 days old, and Experiment 2 targeted calves less than 1 day old. Faecal and blood samples were collected for microbial, pathogen and blood analyses. Results: Probiotic-fed calves (LA group) showed significantly increased gut microbial diversity on Day 10 compared to Day 0 and control group (C group), as indicated by higher Shannon and Simpson indices. Beneficial bacteria such as Faecalibacterium prausnitzii showed higher abundance, whereas potentially harmful bacteria like Bacteroides fragilis showed lower abundance. On Day 20, pathogens were detected in 25% of calves in the LA group, compared to 100% in the C group, which was significantly lower. Blood parameters in the LA group remained stable, whereas the C group showed fluctuations. Mild metabolic acidosis was observed in the C group in Experiment 2. In Experiment 2, the LA group had significantly higher total protein and γ-globulin than the C group on Day 5. Conclusions: The LA group showed beneficial bacteria proliferation, harmful bacteria suppression, pathogenic infection inhibition and improved serum protein status, suggesting that these strains may contribute to the health management of calves under 10 days old.