Isolation and identification of Mycoplasma synoviae in Hebei, China, and evaluation of the immune protection efficacy of inactivated vaccines.

Mycoplasma synoviae (MS) causes infectious synovitis and eggshell abnormalities in chickens, leading to major economic losses. Vaccination is essential for control, but strain differences often reduce effectiveness. To develop a region-specific inactivated vaccine, MS strains were isolated from poultry farms, and a highly virulent strain (CD-1) was selected using embryo infection assays. A chicken-challenge model identified footpad injection of 0.2 mL at 10⁸ CCU/mL as the optimal infection method. Inactivated vaccines using CD-1 (10¹⁰ CCU/mL) with white oil or propolis adjuvants were tested. The propolis-based vaccine showed the best protection, reaching 80 % efficacy at 0.3 mL/bird, outperforming the white oil and commercial vaccines. This study supports the development of targeted MS vaccines for Hebei.