Evaluation of the effects of an HVT-IBD vector vaccine on the immune system of layer pullets in comparison with two commercial live IBD vaccines




Herpes virus of turkeys (HVT)-vectored vaccines have been experimentally tested in a variety of studies in meat-type birds and shawn to be efficient and safe. Not much is known about the influence of a vector HVT-infectious bursal disease (IBD) vaccine on the development of immunity in layer pullets. Our objective was to compare the effects of vaccination with an HVT-IBD vector vaccine on the immune system and on the immune response of layer pullets, in comparison with two commercial infectious bursal disease modified live vaccines, one classified as intermediate and one as intermediate plus, respectively.

One-day old commercial brown pullets were randomly split in four groups and reared in isolation rooms up to 70 days of age. Group 1 was vaccinated with the vector vaccine subcutaneously at day-old. Group 2 and 3 were orally vaccinated with the intermediate or the intermediate plus vaccine, respectively, at 28 days of age to avoid the interference of maternally derived antibodies. Group 4 was not vaccinated against IBD. Ali groups were additionally vaccinated with a Rispens vaccine and with live infectious bronchitis and Newcastle disease vaccines, before a booster vaccination with an inactivated vaccine containing infectious bronchitis, Newcastle disease and EDS76 antigens. Blood samples were collected at day 1, 14, 21, 28, 35, 42 and lastly at day 70 of age when the experiment concluded with the necropsy of pullets. At post-mortem examination significantly higher bursa to body weight ratios were recorded in the group vaccinated with the vector vaccine versus the ether groups vaccinated.

Live infectious bursal disease vaccines reduced the number of circulating B lymphocytes at day 42, in comparison to the HVT-IBD-vaccinated and to the control groups. Additionally, higher antibody titres were detected against Newcastle disease, infectious bronchitis and EDS76 in the HVT-IBD group as compared to the ether groups, indicating an impairment ofthe B cells responsiveness in the IBD live vaccinated chickens.