Studies on the correlation between the results of the haemagglutination-inhibition test and the immunity against Newcastle disease
Balla, L.; Papócsi, L.; Szurop, I.; Tóth, B.
Acta Veterinaria Academiae Scientiarum Hungaricae 26(2): 235-242
1976
ISSN/ISBN: 0001-7205 PMID: 1031255 Document Number: 106848
The immune state of of virulent virus. HI test serum was sampled from approximately 1% of the birds in large scale poultry farms 2-3 wk after vaccinations at 10-14, 35 and 56 days with the La Sota strain, as well as at 13 wk of age with the H strain. These birds provided reliable information about the actual immune state of the clocks. The HI test was regarded as suitable for checking the efficiency of routine large scale immunization programs. In 69.5% of the flocks tested the percentages of seropositive and immune birds were identical or differed only slightly. High percentage of HI positive birds, especially of those having titers above 1:8, was a precise indicator of firm flock immunity. The HI results obtained 6-10 wk after drinking water application of La Sota vaccine at 10-14 days of age, or 6-12 mo. after s.c. injection of H vaccine at 13 wk of age, did not precisely indicate the actual immune state. The serological assay did not reliably yield information about the protection of chick groups possessing material ND antibodies (tested when 2-3 days old) or about chicks originating from vaccinated parent flocks and immunized by drinking water vaccination at 2-7 days of age.