RESPONSES OF GREY-BLACK BROAD-BREASTED TURKEYS (MELEAGRIS-GALLOPAVO) OF UGANDA TO NEWCASTLE-DISEASE VACCINE VIRUS

Three weeks after hatching, 100 male turkey poults of grey-black broad breasted trait, in duplicate, were vaccinated for Newcastle disease ( ND). Their humoral immune response to B1 and La sota ND virus (NDV) me asured by the Heamagglutination-inhibition (HI) test were examined and used to assess the host factor effect of indigenous turkeys on the ND V efficacy. The results revealed a statistically significant differenc e (P < 0.5) in ND HI antibody titres between B1 and La sota NDV vaccin ated turkeys. The mean HI titres of B1 NDV vaccinated turkeys of 0.49 (single virus dose of 10(6.5)EID(50)/bird) and 0.59 (double virus dose of 2 x 10(6.5)EID(50)/bird) were not significantly different (P > 0.0 5) from that (0.42) of the controls (non-vaccinated turkeys) indicatin g that, the B1 vaccinated turkeys did not seroconvert for NDV. Mean ND HI antibody titres of 2.3 (at virus dose of 10(6.5)EID(50)/bird) and 3.4 (at double virus dose of 2 x 10(6.5)EID(50)/bird) were observed in La sota NDV vaccinated turkeys. However, the double dose of La sota N DV gave an earlier and higher HI antibody response. The HI antibody ti tres to the La sota NDV vaccinated turkeys of the 2 groups were signif icantly different (p < 0.05) from each other. The indigenous grey-blac k broad-breasted turkeys showed some degree of resistance to both B1 a nd La sota NDV, but with the B1 NDV being more affected. It was conclu ded that some indigenous turkeys in Uganda are fairly resistant to the less virulent strains of NDV (notably the B1 strain) and may limit th e efficacy of the ND vaccine virus leading to vaccination failures in such birds.