Commercial production of broiler and layer flock is dependent on the immunological status of the birds. Genetically determined immunocompetence and environmental factors are responsible for varying susceptibility or resistance to infectious diseases of chicken. The primary and secondary lymphoid organs are the main components of immune system in vertebrates. understanding age-related immunocompetence by evaluating circulating T lymphocyte population in apparently healthy commercially raised chicken is of direct relevance to developing breeding strategies as well as promoting health measures...