[Effectiveness of Deptavac HVT vaccine on broiler parents during the egg-laying period]

Experiments were carried out with 4 flocks-a total of 16,940 layers of the White Plymouth Rock breed (10,865 vaccinated and 6075 untreated) and 3000 cocks of the White Cornish breed (502 vaccinated and 1498 untreated). The test birds had been vaccinated at the age of one day. The average month mortality rate among the vaccinated birds was 1.5 per cent, and among the untreated it was 4.9 per cent; for the whole exploitation period these values were 15.35 and 47.17 per cent, respectively. Mortality rate caused by Marek's disease and lymphoid leukosis (specific mortality) in the test groups was 4 times lower as compared with that of the control groups (11.54 as against 44.75 per cent), and the coefficient of epizootiologic effectiveness was 74.4 per cent. Considerable variation was established in the intensity and dynamics of the epizootic process with the vaccinated and unvaccinated birds, on the one hand, and the layers and cocks, on the other. White Cornish cocks proved more resistant to Marek's disease and more sensitive to lymphoid leukosis, while the layers of the White Plymouth Rock breed were more sensitive to Marek's disease and more resistant to lymphoid leukosis. These differences could explain the dynamics peculiarity of the specific mortality exhibited by layers and cocks. The egg-laying capacity of a "forage" layer up to the age of 62 weeks of age in the test flocks was 9.2 (7.2) per cent higher than that of the untreated layers. In exploitation up to the 70th week of age each test layer gave 23 eggs more as compared to the untreated. It is calculated on the basis of the experimental data that a total of 55,200 eggs and more could be obtained from 6000 parental birds vaccinated against Marek's disease during a 10-month laying period.