Effect of spraying Bacillus coagulans during incubation on hatchability, chick growth, resistance to Mycoplasma synoviae, and cecal microbiota

Mycoplasma synoviae ( MS ) causes synovitis and airsacculitis in laying hens, reducing production performance and resulting in economic losses. Leveraging the acid-intolerant nature of MS, this study sprayed acid-producing Bacillus coagulans ( B. coagulans ) during incubation, investigating the effects on hatchability, chick growth, resistance to MS, and cecal microbiota. For this study, hatching eggs in the treatment group were sprayed with either B. coagulans or saline, with a conventional incubation group serving as the control. Results indicated that the B. coagulans sprayed group exhibited a higher percentage of healthy day-old chicks compared to other groups ( P < 0.01). Post-hatch, chicks were divided into five groups based on treatments during incubation and post-hatch: Group A (sprayed with B. coagulans + provided drinking water), Group B (sprayed with sterile saline + fed with B. coagulans) , Group C (sprayed with sterile saline + provided drinking water), Group D (sprayed with sterile saline + fed with antibiotics), Group E (sprayed with B. coagulans + fed with antibiotics). Results indicated that Group A demonstrated superior growth performance during the first week. At 21 days of age, Group A showed a lower MS infection rate compared to all other groups ( P < 0.01), while serum levels of IL-10, IgA, and IgG were upregulated in Groups A and E ( P < 0.01). 16S rRNA sequencing analysis revealed that B. coagulans spray treatment improved cecal microbiota homogeneity and increased the relative abundance of Eubacterium coprostanoligenes ( E. coprostanoligenes ) and Negativibacillus ( P < 0.05), promoting enrichment of short-chain fatty acid-producing genera. Further analysis revealed a positive correlation between the relative abundance of E. coprostanoligenes and MS resistance, suggesting its colonization advantage may directly enhance host immunity against MS. In summary, spraying B. coagulans during incubation promoted hatchability, chick growth, resistance to MS, and cecal microbiota. This strategy provides an antibiotic-free solution for MS control, with operational simplicity and sustained efficacy that align with the demands of modern intensive poultry farming.