A study on depletion of maternally-derived antibodies (mda) and response for the intermediate vaccine type against infectious bursal disease (ibd) in a flock of broiler chicken.

Abstract

Infectious Bursa] Disease (IBO) is a highly contagious viral disease affecting young chickens. It is one of the most important diseases causing economic losses to the broiler chicken industry. An effective IBO prevention and control program in broilers must involve a proper biosecurity programme and an effective vaccination programme. Among the vaccine categories available, the intermediate type IBO vaccines are most commonly used in broiler chickens. However, the MDA titer in chicks and the prevailing field strains of IBO virus should be taken into consideration when designing a proper vaccination programme.This present study was conducted with a view to studying the MDA depletion pattern and the response for an intermediate vaccine type against IBO, in broiler chickens. A flock of 100, day-old, Hubbard broiler chicks (DOC) from a vaccinated breeder flock was used for this study .Samples of 10 chicks were bled at day 4 and day 14 of age, using cardiac puncture technique and the serum samples were obtained. The MDA titer in serum was measured using enzyme-linked immunosorbent assay (ELISA) (IDEXX, USA). Then the chicks (n=80) were divided into two groups (groups A & B) and group A (n=40) was given an intermediate type, live vaccine against IBO, Bur 706 (Merial, UK), in drinking water. Samples of IO birds each from both group A & B were bled at day 24 of age, using the wing vein technique and the antibody titer of each sample was measured using ELISA. Subsequently, group A (n=30) was given a booster vaccine of the same type. Samples of IO birds each froð€€¢ both group A & B were bled again at day 34 of age, using the wing vein technique and the antibody titer of each sample was measured using ELISA.The mean maternal antibody titer (MMA T) at day 4 and day 14 were 4346 and I 057 ELISA units, respectively. The mean antibody titer (MAT) of group A was 519 while that of group B was 401, at day 24 of age. Meanwhile the MAT of group A was 640 and that of group B was 296 at day 34 of age.The vaccination of parent flocks is responsible for the higher level of MDA demonstrated by chicks at day 4 of age (Ahmed and Akhter, 2003). It is significantly higher (P<0.05) compared to the MAT of birds after vaccination, at latter stages of life. The MAT of group B at days 4, 14, 24 of age were significantly different (P<0.05) from each other while that of day 24 and day 34 of age showed no significant difference. This significant difference of MAT can be attributed to depletion of MDAs which is not compensated by vaccination. Although the MAT of groups A and B are not significantly different at day 24 of age the importance of a booster vaccination at day 24 of age cannot be overlooked owing to the significant difference of (P<0.05) MAT between A & B, at day 34 of age.This study highlights the importance of vaccination of parent flocks in order to protect chicks from IBO infections at early stages of life. Further, it can be stated that broiler birds that are left unvaccinated have a higher chance of acquiring IBO owing to the rapid rate of maternal antibody depletion occurring in them.