engleski

Testing of the efficacy of broiler protection against IBDV by serological immune response and mortality under the field conditions

IBDV strains that broke through high levels of maternal antibodies in commercial flocks, causing up to 8.6-40.2% mortality rates in broilers and producing lesions typical for IBDV, occurred in Croatia in 1995. The monitoring performed during the period from 1997 to 2000, was carried out in order to differentiate IBDVs present under field conditions as well as to record a follow-up from the vaccinated broiler breeder parents to progeny. The RT-PC/RLFP analysis showed that during this period the vvIBDVs were present in 92% of the IBDV positive bursa samples collected from the commercially reared broilers, while 8% of the IBDVs belonged to classical, probably vaccine strains. The field monitoring comprised 1, 720, 000 broilers at the age of 1 to 40 days and 35 broiler breeder flocks at the age of 1 day to 44 weeks. For the determination of the efficacy of breeder vaccination program, the sera samples collected from at random selected birds, were analysed for the presence of the IBDV antibodies using commercially-available ELISA testes. The mean ELISA titers of the IBDV antibodies in the sera taken from 35-week-old broiler parents amounted to 5513?1757 in 1997, 4834?1696 in 1998, 3562?1295 in 1999, and 3862?160 in 2000, with the respective variability coefficients (CV) 31.8, 31.7, 32.8 and 34.3 expressed in %. At the same time, mean ELISA titers of the maternal IBDV antibodies in the sera of day-old progeny did not significantly differ from those in the breeder sera and amounted to 3075?857 in 1997 ; 3991?1761 in 1998, 3244?1041 in 1999, and 4638?1720 in 2000 with the respective variability coefficients 27.8, 31.1, 35.0 and 34.3 expressed in %. The fact that the appropriate uniform titers of the IBDV active antibodies were generated in breeders and transferred to offspring, gave us opportunity for the application of an intermediate vaccine for the broiler protection and a consequent decrease in mortality amounting to between 2.8 and 20.4% was observed.

infectious bursal disease; broilers; vaccination

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