Novel Limoisilactobacillus reuteri and Helianthus tuberoses synbiotic improved faecal biomarkers, antioxidant status and influenced the fecal microbial antibiotic sensitivity in neonatal dairy calves

Antibiotic growth promoters (AGPs) are commonly used in neonatal dairy calves to prevent diarrhea and enhance early growth performance. However, their extensive use contributes to antimicrobial resistance (AMR). This study evaluated the potential of a calf fecal-origin probiotic-based synbiotic as an alternative to AGP tetracycline (TET) in influencing fecal biomarkers, antioxidant status, and the gut resistome in neonatal dairy calves. Eighteen newborn Vrindavani calves’ hand-fed milk, were randomly assigned to three groups (n = 6): no supplementation (CON), TET (1 mg/kg body weight) for 2 weeks, and synbiotic (SYN Limosilactobacillus reuteri RM125 (3–5×10⁸ cfu/mL) and Jerusalem artichoke tuber ( Helianthus tuberoses , JAT) powder (2% of dry matter intake) for 12 weeks. The calves were provided free access to forage and calf starter. Rectal fecal samples collected at 0, 1, 2, 3, 4, 6, 8, 10, and 12 week to assess gut health parameters. Fresh fecal samples were subjected to weekly antibiotic sensitivity tests against six representative antibiotics. Serum samples collected at weeks 0, 6, and 12 were analyzed for biochemical and antioxidant markers. The SYN group showed a significant (P < 0.05) increase in fecal Lactobacillus and Bifidobacteria counts, along with significantly (P < 0.05) reduced pH and ammonia levels, and improved lactic acid and short-chain fatty acids, indicating enhanced gut health. The serum lipid profile significantly (P < 0.05) improved in SYN calves, while liver and kidney function indices and serum mineral status remained comparable across the groups. Antioxidant status improved in the SYN group, with higher malondialdehyde (MDA) and catalase (CAT) enzyme activity. Among the six antibiotics viz, tetracycline, ciprofloxacin, ampicillin, ceftriaxone, cotrimoxazole and chloramphenicol, the fecal microbiome of SYN calves exhibited significantly (P < 0.05) higher zones of inhibition for ciprofloxacin and ceftriaxone, suggesting a favorable shift in the gut resistome. These findings suggest that synbiotic containing calf fecal-origin L. reuteri RM125 and JAT is a promising alternative to AGPs for enhancing fecal biomarkers, antioxidant status, and gut microbial resistance in neonatal dairy calves.