The increasing global demand for sustainable agricultural practices and the quest for food security has intensified the need for alternative solutions to promote healthy growth in farm animals. One potential strategy is the use of probiotics derived from diverse sources, which remains relatively uncharted. In this context, this study aimed to assess the probiotic potentials of Bacillus velezensis D01Ca and Bacillus siamensis G01Bb, strains sourced from the gut of ducks and goats. Using two completely randomized experimental designs with 150-day-old broiler chickens, two distinct set-ups were implemented. In the first, broilers were subjected to either a control condition, a single dose of B. velezensis D01Ca at 2.4 × 10⁷ cfu/ml, or its double dose. The second set-up followed a similar setup, but with B. siamensis G01Bb at 2.29 × 10⁷ cfu/ml. Throughout the 42-day trial, all broilers consumed a commercial ration ad libitum and accessed water freely, with specific groups receiving the supplemented water based on the treatment. Results show that the feed intake of broilers remained unaffected by the probiotic supplementation, with no significant difference (P≤0.05). However, broilers in the supplemented groups exhibited a noticeable increase in body weight and body weight gain when compared to the control. The feed conversion ratio, crucially, was consistent across all test groups. Conclusively, our findings suggest that B. velezensis D01Ca and B. siamensis G01Bb hold promise as viable probiotics for broiler chickens, offering potential strides toward sustainable agricultural practices and enhanced food security.

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