Beak trimming was a part of routine husbandry for poultry industry,which was the most efficient and economic way to reduce the incidence of cannibalism.However,the controversy about young chicken trimming still exits and it was drawing more concern recently along with the popular of animal behavior and welfare theory.To evaluate the influence of beak trimming on young chicken spleen development and find the key regulators of the spleen development,in this study,the electron microscope technique,flow cytometry and immunohistochemical techniques were used to investigate the effects of beak trimming stress on the spleen development.The result of electronic microscope showed that significant stress response could be found in chicken spleen cells after beak trimming.Cell volume became larger,chromatin of cell nuclear agglutinated conglobation,cytoplasm formed more vacuole,and mitochondria emerged vacuolization phenomenon in splenic lymphocyte after beak trimming.From the flow cytometry,the lymphocyte of spleen in the control group and experimental group were mainly in G1phase,and the remaining small amount was in S and M phases.Of interest,the number of the lymphocyte which are in G1phase within immune organ in the experimental group were more than that in the control group,but the number of cells in S and M phases were less than that in the control group.And beak trimming decreased the lymphocytes proliferation index of spleen.Inmmuohistochemical result showed that the beak trimming stress did not affect the expression sites of two apoptosis-related genes,Bcl-2 and Bax,in the spleen.But the expression level of Bcl-2 decreased while Bax increased in chicken immune organs after beak trimming.Furthermore,the beak trimming increased spleen cell apoptosis with a time-dependant style. Our findings may make a contribution to the active precaution of stress response.