Newcastle disease is an economically important disease of poultry resulting in huge economic losses every year to the poultry farmers in Pakistan. To compare passive immunization and active immunization during outbreak of Newcastle disease a total of 140 chicks at 16th day of age were divided into seven groups (A, B, C, D, E, F and G) containing 20 birds in each. The level of maternal antibody in chicks, was determined by haemagglutination inhibition titres which revealed that it was the highest at one day and decreased with increasing age. Newcastle disease virus gifted from Dr. Shafqat Fatima Rehmani, Director, Poultry Vaccine Center, Karachi, Sindh was pathotyped by using MDT and ICPI. The Embryo Lethal Dose5o was calculated to be 1083h/0. imi and was found highly pathogenic. Infection was induced in birds through administrating 100 ELD5O1O631/0.lml of Velogenic Newcastle disease virus. Birds of group A, this group seved as a negative control. In group B, this group acted as a positive control. Infection was given by using 0.1 ml of 100 ELD50 of Velogenic Newcastle disease virus intranasally at 26 days of age. In group C, at 16th days of age, all birds in this group were vaccinated with Newcastle disease virus vaccine. At 26th day of age, this group was exposed to infection as mentioned above. In group D, at 24th days of age, all birds in this group were vaccinated with Newcastle disease virus vaccine. At 26th day of age, infection was given by using 0.1 ml of 100 ELD50 of VNDV intranasally into individual bird.

In group E, infection and vaccination were given simultaneously at 31 day of age. In group F, In this group, infection was given by using 0.lml of 100 ELD50 of VNDV intranasally, at 26 days of age. When Newcastle disease symptoms were noticed, birds were vaccinated with lentogenic strain of Newcastle disease virus vaccine (Lasota, TAD- Germany) by using 0.5mllbird orally.

In group G, infection was given by using O.lml of 100 ELD50 of VND.V intranasally, at 26 days of age. When Newcastle disease symptoms were induced, birds were treated with 64 units of anti-NDV-haemagglutination inhibition yolk antibodies. Use of Lasota vaccine and preformed antibodies in yolk help in decreasing economical losses due to outbreak of Newcastle disease in poultry.