EN
The influence of vaccination of 18 old hen’s embryos with HVT virus against Marek’s disease on the process of hatching was assessed. There was noted an egg shell pipping, pipping time, hatching time and the indices of hatching in vaccinated and control embryos. The degree of lesions of embryos dead between day 19—20 and the level of total protein (B„) and immunoglobulins (Ig) in the plasma of chickens after hatching were determined. It was found that chickens vaccinated in the embryonal period prolonged egg shell pipping, hatching time and started hatching with a 5 hour delay. Besides, the index of hatching was at 6 per cent lower than that in controls. The dead embryos showed the swellings of chorioallantois membranes, oedema of kidneys and defects of location which pointed to a developmental retardation. Female chickens vaccinated had a higher level of total protein (p<0.05) and immunoglobulins compared with those of controls. Because of lossess in hatches the method of embryos vaccination needs further studies.