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.