5Abd-el-Motelib T Y,Kleven S H. Acomparative study of My- coplasma gallisepticum vaccines in young chicken[J]. Avian Dis, 1993,37(4) :981-987.
6Evans R D,Hafez Y S. Evaluation of a Mycoplaksma gallisepti- cum strain exhibiting reduced virulence for prevention and control of poultry mycoplasmosis[J] Avian Dis,1992,36(2) : 197-201.
7Jackwood M W. Review of infectious bronchitis virus around theworld [J] .Avian Dis, 2012, 56 (4) 634-641.