The aim of this study was a comparison of the occurrence and presence of Mareks disease strain HVT FC 126 in internal organs after in ovo vaccination and after vaccination of one day old chicks. One hundred SPF chicken embryos were used in the experiment on the 18th day of incubation. Forty-five embryos were vaccinated in ovo with a dose of 2400 pfu of virus HVT FC 126. Twenty-eight embryos were injected in the back area (group I), and for 17 embryos the vaccine was provided to the embryonic fluids (group II). All of the embryos were hatched. Chicks from non-vaccinated embryos were divided into two groups. On the first day after clutch, 30 chicks were vaccinated in the leg muscle (group III). The fourth control group consisted of non-vaccinated chicks. Blood samples and sections of the liver, spleen, kidneys, and bursa of Fabricius were taken on days 1, 3, 7 and 10 from 5-day-old chicks (group I), on days 1, 3 and 10 from group II, and on days 3, 7 and 10 from groups III and IV. Total DNA was extracted from the samples, and used for the detection of viral DNA with PCR method. For amplification, two primers, specific for the fragment of A gene of MDV 3 serotype were used. No influence of in ovo vaccination on hatching was observed. Percentage of hatched chicks after in ovo vaccination was 85.7% and in the control group 87.3%. Chicks were healthy and welldeveloped. Viral DNA was found in the blood and lungs in group I about 3 hours after hatching, and was detected on the third day of life in blood, liver, spleen, lungs and kidneys of birds from group I as well as in blood samples from group II. From the 7th day of life characteristic for HVT FC 126 product (434 bp) was observed in all the samples collected from group I. It was subsequently detected in blood, spleen and lungs on the 7th day of life and in the bursa of Fabricius and liver on the 10th day of life in group III. Viral DNA was not found in samples taken from the heart and kidneys.
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