Vaccination against Newcastle disease: An assessment of haemagglutination inhibition titres obtained from field samples
Phillips, J.M.
Veterinary Record 93(22): 577-583
1973
ISSN/ISBN: 0042-4900 PMID: 4785347 Document Number: 65522
The HI test was used, since it is the best alternative to challenge of a vaccinated flock with a Newcastle disease virus of known virulence. Data suggest that titres of log25 and log27 are necessary to protect against mortality and egg loss, respectively. 1042 blood samples were divided into six groups according to flock vaccination procedures. In the group where birds had received live vaccines only (Hitchner B1 and LaSota in single or repeated applications), log2T means ranged from 2.9-7, but in all other groups (receiving live vaccines as well as injected inactivated vaccine), log2T means generally ranged from 4.9-9.9, which showed satisfactory protection against mortality. One group of samples from a flock naturally exposed to Newcastle disease gave log2T means above 10. Apart from this, the group best protected against egg loss had received live vaccine during rearing, inactivated vaccine at point-of-lay, and live vaccine during the laying period. This last administration of live vaccine produced both higher and more uniform titres than were otherwise achieved. Of the other groups, which had not received vaccine during the laying period, highest titres were obtained when vaccination during rearing and at point-of-lay was by live vaccine and inactivated vaccine respectively, rather than by inactivated vaccine in both cases, but in these groups protection against egg loss was not always ensured.