Pathogenicity, immunogenicity, and cross-protective efficacy of representative Eimeria brunetti strains in Chinese yellow-feathered broilers: an in vivo evaluation.

Biological characterization of geographic strains of Eimeria brunetti was conducted to inform control strategies. The prepatent period was consistent (118-122 h) across strains, though the Baoding 2 strain exhibited the highest reproductive capacity while the Zhangzhou strain induced the most severe intestinal lesions. Infection significantly impaired weight gain and intestinal integrity, with optimal oocyst sporulation occurring at 25% litter moisture. Immunization with field strains elevated IgY levels and modulated cytokine responses. Upon challenge, immunized birds demonstrated improved weight gain, reduced lesions, and markedly lower oocyst output. Notably, an attenuated precocious strain conferred strong protection, reducing oocyst shedding by 93.61-99.92%. These findings demonstrate the significant pathogenicity of E. brunetti in Chinese yellow-feathered broilers and establish substantial cross-protection among geographic strains, supporting the potential for a broadly effective vaccine. The attenuated precocious line represents a promising vaccine candidate that could help address this gap in protection.