study on subclinical and clinical marek's disease (md) in the broiler chickens using histopathology

marek's disease (md) is the most common lymphoproliferative diseases of chickens; during the last year the incidence of md was  investigated among slaughter houses and suspected broiler farms, located in  isfahan (iran) as the region of  highest density of poultry husbandry by histopathology,  for subclinical md investigation, in  total 1550 chickens originated  from slaughter houses  were examined, parallely  for clinical  md investigation, 100 chickens  from  10 broiler farms were examined.based on the obtained results, about 6.81% of the liver samples (with average age of 60 days) collected from slaughter houses showed pleomorphic lymphoid cell proliferation  and  infiltration of  mononuclear  cells as subclinical md. the microscopic results of examined broilers (average age of 57 days) with clinical signs of md , showed  pleomorphic  lymphoid cell proliferation in sciatic nerves (62%) ,  spleens (66% )  and livers(71%). now in iran, the outbreaks of subclinical and clinical md in broiler chickens increased  but md vaccination is not permitted so regarding to the results it will be to an obligation for hatchery  md vaccination, and/or decreasing the slaughtering age  besides a good bio security  of broilers farms