Comparative Evaluation of Humoral Antibody Responses to Various Newcastle Disease Vaccines in Chickens

Newcastle Disease (ND) remains a significant threat to poultry production in Ethiopia. Although various vaccines are used to control the disease, there is limited information on their comparative efficacy across different vaccine types and chicken breeds. Therefore, this experimental study was conducted from October 2024 to January 2025 at Andassa Livestock Research Center's poultry farm to evaluate the humoral antibody response of ND vaccines in Tillili and Koekoek chicken breeds. A 2 × 4 factorial completely randomized design was used with 480 day-old chicks (240 Tillili and 240 Koekoek), randomly assigned to 24 pens (20 birds each). Blood samples (1,092) were collected before and after vaccination, with 964 successfully processed to measure ND antibody titers by indirect ELISA. The vaccines used for the experiment were I2 thermostable, LaSota, and HB1. The positive control was the standard check currently used in Ethiopia: HB1 for chickens at 7 weeks of age and LaSota for chickens of the remaining ages. Independent and paired t-tests compared the mean antibody titers between treatment and control groups before and after vaccination. Multiple linear regression analyzed the factors affecting antibody titers, while Cox regression evaluated their impact on chicken mortality rates. Overall, chick mortality was 4.6%, with 76% developing protective ND antibody levels across treatments. Koekoek chickens had significantly higher maternal antibody levels (mean titer 4,460.3) than Tillili chickens (mean titer 202.3) during the first week. A relatively higher antibody response (5475.4 ± 2821.1) was observed in Koekoek chickens compared to Tillili chickens (4200.9 ± 2092.8). Overall, antibody responses were higher at 42 days post-vaccination with I2 thermostable vaccines (6031.2 ± 420.2). Antibody levels differed significantly across bleeding dates (P = 0.0274) and between treatment groups (P = 0.0002). However, an independent t-test comparing the positive control and treatment groups revealed no significant difference (P = 0.1954) in antibody responses. The multiple linear regression analysis indicated that sex (P = 0.0172), bleeding time (P = 0.001), and age (P = 0.000) were statistically significant factors associated with the mean antibody titer. In conclusion, all three vaccines elicited higher antibody titers, with the positive control achieving the highest antibody titers, followed by the I2 thermostable vaccine. This suggests that the I2 thermostable vaccine offers comparable practical advantages for field use, particularly in areas where cold chain facilities are limited.