Effects of multiple La Sota vaccinations on the atrophy of the lymphoid organs associated with velogenic Newcastle disease virus infection in pullets.

This research evaluated the effects of multiple La Sota vaccinations on atrophy of the lymphoid organs associated with the velogenic Newcastle disease virus (vNDV) infection in pullets. Two hundred pullets were randomly assigned into five groups designated as unvaccinated unchallenged {UU}, unvaccinated challenged {UC}, La Sota 1 {L1}, La Sota 2 {L2} and La Sota 3 {L3}. At three weeks old, pullets in groups L1, L2 and L3 were vaccinated with La Sota vaccine. At five weeks, L2 and L3 groups received a second dose of the vaccine. At 7 weeks, only L3 group received the third dose. At ten weeks, birds in vaccinated and UC groups were challenged with 0.1 ml of vNDV Kudu 113 intramuscularly. Clinical signs of ND and mortality were observed in UC on days 2 and 3 post challenged (PC) while no mortality was observed in vaccinated groups. Atrophy of the lymphoid organs observed in vaccinated groups was more severe in L3 on days 3 and 7 PC. On days 7, 14 and 21 PC, antibody titre was higher in L1 and L2 than in L3. This study showed that multiple La Sota vaccinations up to 3 successive times cause severe atrophy of the lymphoid organs.