The study was conducted to determine the persistence of maternally derived antibody (MDA) and its effects on protection against NDV in broiler chickens and to investigate the status of humoral immune response following vaccination with BCRDV® (F-strain, lentogenic) at different ages of broiler chickens during the period from August to October, 2008. A total of 90 day-old broiler chicks of Cobb 500 strain with the history of vaccination of parent stock against Newcastle disease (ND) was divided into three groups (A, B and C). Birds of group A (n = 35) were used for the study of protection ability of MDA against NDV, the birds of group B (n = 45) were used for the measurement of humoral immune response in chickens following vaccination at different ages and birds of group C (n = 10) were used for the determination of persistence of maternally derived antibody. The level of antibody titre against NDV was determined by HI test. The protective potentiality of MDA and vaccine was determined by the rate of survivability of the chickens following challenge infection. It was observed that the MDA titre in day-old chicks was higher and gradually declined at minimal level at day 28. The MDA titre of 128 or above protected the birds following challenge infection with virulent NDV. There were significant decrease in HI titres of chickens which were vaccinated once at day 1 and day 7, and could not withstand challenge infection with virulent NDV. Single vaccination with BCRDV® at day 14 triggered the production of antibody but could not provide complete protection to the birds. The birds which were boosted with the same vaccine 7 days and 21 days after primary vaccination produced better immune response. However, the birds which were vaccinated primarily at day 1 and boosted at day 7 could not withstand the challenge completely. Of the other regimens of twice vaccination, primary vaccination at day 7 and booster dosing at day 28 was found to be the best in terms of immune response and protection potentiality. Therefore, it may be concluded that (a) The MDA titre level of 128 or above is sufficient to protect broilers against challenge with virulent NDV,( b) Primary vaccination at day 7 followed by a booster dosing at day 28 may be followed for better immune response and protection against ND in broilers.DOI: 10.3329/bjvm.v7i2.5995Bangl. J. Vet. Med. (2009). 7(2) : 296 – 302
EVALUATION OF MATERNALLY DERIVED ANTIBODIES AGAINST NEWCASTLE DISEASE VIRUS AND ITS EFFECT ON VACCINATION IN BROILER CHICKS