Introduction: Neospora caninum is an intracellular protozoan considered as a serious disease agent in cattle and dogs. In the present study, N. caninum tachyzoites were cultivated in mouse macrophage cell line and Vero cell line.
 
Materials & Methods: The number of harvested tachyzoites was recorded daily. After parasite propagation and continuous passages, chicken embryonated eggs were used for comparison of tachyzoites attenuation. Mortality rate was recorded daily and the tissue samples of brain, liver, and heart were taken for histopathological examination.
 
Findings: Mortality rate in embryonated eggs inoculated with N. caninum harvested from Vero and mouse macrophage cell line was 100% and 10%, respectively, which was dose-dependent. Microscopically, there were milder hepatitis and myocarditis in the liver and heart of chickens inoculated with N. caninum harvested from mouse macrophage cell line.
 
Discussion & Conclusions: The present findings showed that cultivation of N. caninum tachyzoites in macrophage cell line increased propagation of tachyzoites and also reduced attenuation of the parasite. These results suggested the suitable cell line for mass production of N. caninum tachyzoites for various experimental researches and also producing live attenuated vaccine.