Abstract
Mycoplasma synoviae (MS) infection predominantly manifests as lower respiratory symptoms but also leads to reduced egg production and increased culling rates in laying hens, causing significant economic losses throughout the production cycle. Vaccination remains the most cost-effective strategy to protect layers from MS infection. Previous studies from our laboratory identified and screened immunogenic proteins of MS, culminating in the development of a subunit vaccine that provided robust protection with a two-dose immunization. Building on these findings, this study evaluated various formulations, antigen combinations, and adjuvants of MS inactivated vaccines, tailored to meet field immunization protocols and disease prevention needs. The results indicated that an inactivated vaccine combining whole-cell and subunit components of MS offered effective protection in layers during the pullet-rearing phase with a single immunization. Interestingly, vaccine-induced antibody levels did not strongly correlate with protective efficacy, underscoring the importance of host cellular immunity in combating MS infection. In conclusion, this study addresses field-relevant challenges and presents innovative strategies for MS control in laying hens, offering practical insights for improving disease control and flock management.