Immunologic responses of Philippine native and commercial broiler chickens to heat stress

The study compared the immunologic responses of the Philippine native and commercial broiler chickens to hot environment, specifically on the lymphocyte count, antibody titer, and the histopathology of the bursa of Fabricius and spleen. Forty-five Philippine natives and 45 commercial broiler day-old chicks were subjected to brooding for 14 days. The birds were vaccinated against Newcastle Disease Virus (ND-B1-B1) La Sota strain on day 14, after which they were acclimated at comfort zone up to day 21. On day 22, the birds were subjected to the following environmental settings for five hours a day using the Biotronnette chambers: T1 - comfort zone (21 deg C, RH 20 percent plus or minus 5); T2 - warm arid (28 deg C, RH 23 percent plus or minus 5); T3 - warm humid (28 deg C, RH 80 deg C plus or minus 5); T4 - hot and (35 deg C, RH 20 percent plus or minus 5); T5 - hot humid (35 deg C, RH 20 percent plus or minus 5). Lymphocyte count and antibody titer were determined on days 28, 35, and 42 while the bursa of Fabricius and spleen were taken for histopathologic examination on day 43. Results showed that environment did not affect lymphocyte count of both strains. Mean antibody titer of native chickens were higher (P less than .05) than those of commercial broiler chickens, both in HA-HI and ELISA tests. Significantly higher (P less than 0.01) antibody titers were obtained in the native chickens exposed to hot environment especially at age 42 days when HA-HI test was used. Both strains of chickens tended to decrease their antibody titers as the birds were subjected to higher environment settings. Similar observation was obtained when ELISA test was used. Significantly higher antibody titers were noted in the native than in the broiler especially as exposure time is increased. Histologic examination of the bursa of Fabricius of native and broiler chickens showed different degrees of vacuolation in the epithelial lining as well as increased number of small lymphocytes which is indicative of lymphoid hyperplasia. The presence of cystic formation confirm lymphocyte depletion which further correlates to the decrease in antibody titer