Histopathological Assessment and In Ovo Vaccination Response to IBD and ND in Broiler Chickens

Infectious bursal disease (IBD) is a viral disease that most commonly affects young chickens and destroys lymphocytes, leading to immunosuppression. The field study aimed to investigate the effect of three different vaccines administered in ovo against IBD and spray against Newcastle disease (ND) on serological response tested for IBD and ND and histopathological analysis of the bursa of Fabricius (BF) and quantitative B lymphocytes in BF in broiler chickens. The study was conducted on a farm of four hen houses with 30,000 chicks in each building. Three different vaccination programs were used in the poultry hatchery, and one hen house IV was not vaccinated. All three groups were vaccinated at 18 days and 9 h in ovo during egg transfer against IBD at a dose of 0.05 mL/embryo, group I vector vaccine (strain vHVT013-69), group II immunocomplex vaccine (strain Winterfield 2512), group III immunocomplex vaccine (strain M.B, 0.05). Then, after hatching, the chicks were vaccinated in a spray (groups I, II, and III) against NDV (strain VG/GA, 20 mL/100 birds) and infectious bronchitis (IBV) in a spray (strain H-120, serotype Mass, and strain CR88121, serotype 793B) at a dose of 20 mL/100 chicks. On days 1, 21, 31, and 41, blood was collected for serological tests to determine the antibody titer against IBD, which was performed using two tests (IDEXX and ID-Vet) and against ND. During the necropsy of birds on days 21 and 31, the bursae of Fabricius were collected from five chickens for histopathological evaluation of BF and quantitative B lymphocyte counts; a total of 40 bursae were analyzed (10 per group). The vaccination program applied significantly (<i>p</i> < 0.05) affected the immune response expressed as a geometric mean titer (GMT) in the serum of the examined chickens against IBDV on days 21, 31, and 41. Differences were also demonstrated in the mass and level of BF damage and the number of B lymphocytes. No significant differences were demonstrated in the GMT in the serum of the examined chickens against NDV depending on the vaccination program applied.