Reza Shayestehmehr - Undergraduate student,Fuculty of veterinary Mediciane , Amol University of Special ModernTechnologies , Amol , Iran
Yashar Sarhangzadeh - Master's degree in Animal Science, Livestock and Poultry Physiology

Newcastle disease is a viral disease. This disease was first diagnosed in ۱۹۲۶ in Newcastle, England. Newcastle disease is one of the most important diseases of birds that are raised industrially and intensively, and many flocks of broilers are affected by this disease if they are not vaccinated. be. This disease was identified in Iran in ۱۳۲۹.The symptoms of Newcastle vary according to the type of virus, the level of health and age of the bird and the host species. Vaccination is a sure way to prevent birds from contracting this viral disease. The aim of the present study is to evaluate the most effective time of administration of the killed Newcastle disease vaccine in broilers. The study method is analytical and case-control type. ۴۰ case farms and ۴۰ control farms were selected for the study. The case farm was defined as a farm that had losses of more than ۷% along with clinical criteria, necropsy, molecular testing and disease outbreak history in the region confirming Newcastle disease. The control farms had natural losses (below seven percent) and were free of any disease in the current and previous periods. The control farms were grouped according to the capacity, breed, and compliance with biological security and management principles with the treated farms. In order to analyze the data, chi-square test and multivariate logistic regression were performed using Stata statistical software.

Immunogenicity, Newcastle disease, killed vaccine, RT-PCR.