Introduction Probiotics are microorganisms that have beneficial effects on the host when supplemented at certain doses (Gibson et al., 2017). Bacillus subtilis, a probiotic strain, has been widely used as a directly fed additive in both humans and animals, with a myriad of benefits (Leistikow et al., 2024). It can optimize gastrointestinal bacterial composition, improve immune and antioxidant capacities, and enhance growth and laying performance (Liu et al., 2024; Pandey et al., 2015).