Route of vaccine administration has a great impact on immunization and protection outcomes in chickens. This study was conducted to compare the effect of different administration routes on the efficacy of a thermoresistant Newcastle disease (ND) vaccine (ND.TR.IR) in chickens. A total of 100 one-day-old specific pathogen-free chicks were divided into five groups (n = 20 chicks per group) and vaccinated through different routes at 10 and 20 days of age. Treatments included no vaccination (control [C]), 1 dose inoculation through eye drop (ED), 1 dose inoculation through drinking water (DW), 1 dose inoculation through feed (FV1), and 10 doses inoculation through feed (FV10). At 20 and 34 days of age, antibody titers were measured against ND virus (NDV) in all the chickens by hemagglutination inhibition (HI) test. Chicks immunized with ND.TR.IR vaccine through different routes of administration also were intramuscularly challenged with a local virulent NDV (vNDV) (Ck/ir/Beh/2011) 14 days after booster vaccination (at 34 days of age). Our results showed that in comparison with the FVs groups, the immunized chicks through ED induced a higher HI antibody titers at 20 days of age (p < 0.05). Meanwhile, vaccination through ED induced higher HI antibody titers at day 34 of age compared with all other groups (p > 0.05). The percentages of the protective HI antibody titers (≥log23) detected in ED and DW groups at 20 days of age were higher than those detected in the FV1 group (p < 0.05). However, routes of vaccination had no significant effect on the rate of protective titers at day 34 of age (100%, 90%, 75%, and 85% for ED, DW, FV1, and FV10, respectively). The percentage of post-NDV challenge survived chickens was not affected by the route of vaccination (p > 0.05), but immunization of chicks with ND.TR.IR in FV1 group provided relatively poorer protection when compared with the other groups (90% vs. 100%, respectively). Altogether, immunization of chicks with ND.TR.IR vaccine through different routes of administration induced protective NDV antibody HI titers, and provided protection against vNDV. However, when the vaccine was administrated through feed, a higher dose of vaccine is recommended.
Keywords: Newcastle disease; antibody titer; challenge; protection; vaccination.