The Pathology of Vaccination of Chickens with Varying Doses of Lentogenic LaSota Strain of Newcastle Disease Virus

Recently, it was demonstrated under laboratory conditions that increased doses of LaSota vaccine increased ND antibody response significantly in chickens. In this study, we have used the same model to investigate whether vaccination with increased doses of lentogenic LaSota strain of Newcastle disease virus are associated with pathological changes in chickens. Four-week-old broiler chickens (n=100) were randomly assigned into four groups of 25 each: ZD, each drenched with phosphate-buffered saline, SD, DD and TD broilers were each drenched with single, double and triple dose of LaSota vaccine, respectively. The chickens were observed for clinical signs and lesions. Serum samples were collected from the chickens in all the groups at weekly intervals post inoculation (PV) and assayed for haemagglutination inhibition (HI) antibodies. The vaccinated broilers showed no morbidity and mortality. Only the bursa of all the vaccinated groups appeared slightly reduced in size on day 10 PV. The histopathological changes were lymphoid hyperplasia and formation of germinal centres in the spleen and caecal tonsils from days 3 to 6 PV and mild depletion of bursal lymphocytes on day 10 PV. Generally, the integrity of the lymphoid organs was intact. Groups DD and TD antibody titres were significantly (P < 0.05) higher than that of the SD on day 21 PV. This suggests that increased doses of LaSota vaccine does not cause pathologic impairment and may be considered in improving the performance of the vaccine in the control of velogenic ND.