Abstract: Eighteen AA chicken were raised at 22℃, and at 30-day-old of age they were stressed for 0 , 5 and 10 h at 41℃. The DNA contents of spleen and bursa, the ratio of apoptosis and the expression of caspase-3 and Bcl-2 in the spleen and bursa were measured by flow cytometry. The results were as follows: Cell ratio of S phase (DNA synthetic phase ) in the spleen was 4.67%,5.11% and 4.78% , that of the bursa was 30.52%,24.71% and 24.04% at 0,5 and 10 h after heat stress respectively. Apoptotic rate of spleen was 0.22%, 0.42% , 0.32% and that of the bursa was 0.32%,0.62% and 0.41%, respectively. The positive ratios of the cells expressing caspase-3 in the spleen was 5.49%, 10.36% and 9.80%; and that in the bursa was 8.60%, 10.51% and 9.41% respectively. The positive ratio of the cells expressing Bcl-2 protein in the spleens was 31.25%, 24.01% and 29.26%, and that of the bursa was 30.24%, 27.10% and 31.54%, respectively. The apoptotic rate of spleens of heat stressed chickens for 5 h was significantly different from those for 0 and 10 h, separately (P<0.05. After heat stress, apoptotic rate and positive expression of caspase-3 in spleen and bursa increased gradually from 0 to 5 h, and then decreased slowly . The changes of apoptotic rate were parallel positively with the changes of caspase-3 expression, but negatively with the changes of Bcl-2 expression in the spleens and bursa during heat stress. It is concluded that the apoptosis of spleen and bursa cells was obviously affected by heat stress and regulated by the expression of caspase-3 and Bcl-2 protein.

Key words: Chicken, Heat stress, Spleen, Bursa, Apoptosis