Research Note: Disease tolerance/resistance and host immune response to experimental infection with Pasteurella...

Indigenous chicken breeds are considered to be more disease tolerant than exotic chicken breeds especially for the bacterial diseases. Nicobari and Vanaraja chicken were evaluated for the survivability/mortality patterns and host immune response after experimental infection with P. multocida A1 isolate. The birds were inoculated with 1.9 × 10⁵ CFU/mL through intraperitoneal (I/P) and intranasal (I/N) routes at 2 different age groups viz., 12 wk and 18 wk. Symptoms, mortality rates, lesions in dead birds were observed; Serum from surviving birds of different groups from both breeds were collected at 5, 14, 21, 28, 35 and 42nd d and specific antibody titers were measured by indirect ELISA. At 12 wk of age, the mortality rates were 100% and 16% in birds inoculated by I/P and I/N routes respectively in Vanaraja birds; whereas the mortality rates were 50% and 16% I/P and I/N routes respectively in Nicobari birds. At 18 wk of age the mortality rates were 16% and 50% for I/P routes in Nicobari and Vanaraja birds respectively. The mortality rates were 16% for I/N route in both Nicobari and Vanaraja birds. Lesions such as necrotic foci on liver, congestion in the liver were observed in dead birds. Serum titers were significantly (P < 0.05) higher in surviving Nicobari birds inoculated through I/P route followed by I/N route. The peak titers were reached on 14th d postinfection and declined thereafter. However, no significant difference was found in I/N route of inoculation between 2 breeds. Nicobari chicken breed showed significantly higher survivability and longer mean death time than Vanaraja germplasm to experimental Pasteuralla infection at both the ages however the survivability rate in both breeds improved at later ages.