Feed restriction was attempted for the control of mortality at broiler farms. Respiratory signs were observed in both restricted-feed flocks and fully fed flocks, but they were less severe in the restricted-feed flocks. The death rate in the fully fed flocks began to rise at the age of 4 wk but did not do so in the restricted-feed flocks. Mortality in the restricted-feed flocks was significantly lower than in the fully fed flocks aged from 3 to 7 wk. The economic performance with restriction feeding was better than that with full feeding as a result of improvements in viability and feed conversion rates. Feed restriction appeared to be beneficial in decreasing the death losses.

Common commercial strain male broilers were intratracheally inoculated with 0.3 ml of fluid containing 10(3.7) embryo infective doses of infectious bronchitis virus (IBV) at 14 days of age and 7.5 x 10(6) colony-forming units of Escherichia coli at 18 days of age. Ascites was detected in 15 out of 100 infected birds, which was significantly higher than in a control group of 100 mock-infected birds (P < 0.01). Some parabronchi were blocked by copious exudate containing heterophils and fibrin in the infected birds at 22 days of age although these findings were not seen in the infected birds at 35 days of age or in birds with ascites. The erythrocyte packed cell volume and right ventricle/total ventricle (RV/TV) ratio of birds with ascites were higher than in birds without ascites. The RV/TV weight ratio for the infected group at the age of 35 days was higher than that of the control group. No IBV or E. coli were recovered from the ascitic birds. These findings suggest that these infectious agents induce ascites in the broilers, and then disappear until the birds suffer from ascites.

To monitor the existence of avian pathogens in laying chicken flocks, specific pathogen-free (SPF) chickens were introduced into two layer farms and reared with laying hens for 12 months. SPF chickens were bled several times after their introduction and examined for their sero-conversion to avian pathogens. As a result, antibodies to eight or ten kinds of pathogens were detected in SPF chickens on each farm. Antibodies to infectious bronchitis virus (IBV), avian nephritis virus, Mycoplasma gallisepticum and M. synoviae were detected early within the first month. Antibody titer to IBV suggested that the laying chickens were infected with IBV repeatedly during the experiment on both farms. However, antibodies to infectious bursal disease virus and 6 pathogens were not detected.

Using the rapid glass plate method, the Newcastle disease virus strain MET95 showed much weaker haemagglutination (HA) activity for chicken erythrocytes than 69 other Newcastle disease viruses, including 56 field strains isolated from chickens reared in Japan between 1988 and 2001. Using erythrocytes from other avian species, only the MET95 strain failed to show HA activity for erythrocytes from ducks, geese or pigeons. The haemagglutinin-neuraminidase protein of the MET95 strain was shown to have unique substitutions of isoleucine for thereonine and leucine at amino acide residues 216 and 552. It is suggested that these two substitutions might relate to the unique HA activity of the MET95 strain. This HA activity may be a useful marker for this strain.