A proventriculus-type of avian infectious bronchitis virus was isolated from diseased fowls in China, and designated as strain IBV - D971. After 120 passages on SPF chicken embryos, an attenuated vaccine was developed and designated as strain IBV-D971P.是什么意思_A proventriculus-type of avian infectious bronchitis virus was isolated from diseased fowls in China, and designated as strain IBV - D971. After 120 passages on SPF chicken embryos, an attenuated vaccine was developed and designated as strain IBV-D971P.在线翻译_英语_读音_用法_例句