A novel probiotic bacterium Bacillus paralicheniformis TATVAM-FAB17 isolated from goat rumen increases milk yield in dairy cattle

Probiotics are live microorganisms that provide advantages to the host animal and are being utilized more frequently as feed additives to improve animal health and performance. This study presents isolation, characterization, in vivo and in vitro toxicity assessment, and a small-scale field-level feeding trial of a potential probiotic bacterium, Bacillus paralicheniformis TATVAM-FAB17, obtained from the rumen of a goat ( Capra hircus ). The culture exhibited tolerance to simulated gastrointestinal conditions, including low pH (2–4), bile salts (0.2–0.4%), lysozyme (100 mg/L), and osmotic stress (up to 8% NaCl). Additionally, the strain demonstrated resilience against phenolic compounds (up to 0.5%), indicating its potential for survival in the hostile intestinal environment. In vitro cytotoxicity assays on Caco-2 and Vero cells confirmed the strain’s safety. A 45-day repeated dose oral safety study with 10 9 CFU/day in a rat model revealed no adverse effects on body weight, feed intake, blood parameters, and histology of vital organs. A small-scale pilot study involving 12 animals ( n = 6 in each group, control and test) with dietary supplementation of B. paralicheniformis TATVAM-FAB17 at a dose of 10 9 CFU/day significantly increased milk yield (Δ = +0.043 L/cow/day, 95% CI: 0.036–0.049, p < 0.001) in dairy cattle, highlighting its potential functional benefit in livestock productivity. Yet, it was a small pilot study and needs to be confirmed in larger trials with multiple herds. Phenotypically, TATVAM-FAB17 is resistant to antibiotics of four antimicrobial classes: β-lactams (ampicillin, oxacillin, benzyl penicillin, and cefoxitin); macrolide/lincosamide (clindamycin); phosphonates (fosfomycin); and polypeptides (bacitracin). Whole genome analysis revealed the presence of antimicrobial resistance genes (ARGs) for the corresponding antimicrobial classes. These ARGs were not flanked by mobile genetic elements or prophages, lacking mobility-associated features, further supporting the culture’s suitability as a potential probiotic candidate. Collectively, these findings suggest that B. paralicheniformis TATVAM-FAB17 is a promising probiotic candidate for application in animal feeds.