Abstract   

    Incidence of infectious bursal disease (IBD) in poultry birds amongst the cases submitted to Divisional Diagnostic Laboratory, Dhodial, Mansehra, NWFP, Pakistan during the years 1994 through 1996 was investigated. Overall incidence of IBD was 3.05+0.04%. Flock size, bird type and vaccination had a significant effect (P<0.01) on the incidence of IBD. Disease incidence was higher (P<0.05) in farms (6.53+0.008%) maintaining flock size of less than one thousand birds. Incidenc~ of IBD was higher (P<O.O5) in broilers (5.13+O.OO2) than in breeders (2.93+O.Ol) and layers (1.08+O.Ol%). Difference in incidence of IBD between breeders and layers was non-significant.. Incidence of IBD was higher (P<O.O5; around 5%) in those flocks which received irregular vaccination or were vaccinated once than in non-vaccinated flocks (1.74+O.OO5) or properly vaccinated flocks (0.91+O.OO2%). Season had no significant effect on incidence of IBD. Age wise incidence or mortality caused by IBD indicated comparatively higher losses (3.93+O.OO9 to 4.90+O.O34%) between the ages of 23 and 34 days. It was concluded that severe losses occurred in flocks maintained under irregular vaccination programe.

Key words: Incidence, infectious bursal disease, poultry birds.