The study on CRD was conducted in the indigenous chicken breeds raising at Viet Lap commune, Tan Yen district, Bac Giang province and industrial chicken raising at some farms in Bac Ninh province. The studied result indicated that there was a difference on the infection and mortality rates of chicken due to CRD by age group, breed and raising pattern. For the industrial chicken fattening at some farms in Bac Ninh province, the highest CRD infection case occurred at age group of 29-45 days old with the infection rate was 15.89 percent and the mortality rate was 7.47 percent
and for the egg-laying hen, the Ross 308 breed faced with the highest infection rate (35.63 percent) and the mortality rate was 6.56 percent. For the indigenous chicken raising at households know as "chickens raise in garden", the infection rate was 11.56 percent and the mortality rate was 11.54 percent. The CRD infection rate also increased by the raising scale, the highest rate occurred at the farms raising 500 chickens upward was 22.44 percent. The main clinic symptoms of chickens suspecting with CRD were thin body, coughing, wheezing and swelling.