Introduction
Newcastle disease (ND) is a highly contagious and often severe disease present worldwide that affect multiple species of birds including domestic poultry. Endemic regions to velogenic ND strains face a difficult challenge to keep this persistent field virus challenge away from their commercial poultry operations in spite of overly vaccinated flocks with live ND vaccines.
Live ND vaccines are an essential piece of a complete vaccination program but vaccination program should not be existed only by them. Until the vector ND vaccines developed, there used to be some common practices with increasing the number of live ND vaccines depending on the higher ND challenges. However, indeed there are consequences of increasing the live ND vaccines such as; post-vaccination reactions, worsen flock uniformities, higher ND virus shedding, and circulation.
Post-vaccination reactions can lead to subtle to overt respiratory signs, because of the inflammation of the trachea. It may worsen in case of suboptimal husbandry conditions (too high stocking density, high ammonia level, wet litter, poor ventilation). As a result, flock uniformity will decrease, and secondary opportunistic respiratory infections (eg, E.coli) may arise with the need to apply antibiotic medication. Ultimately, slaughterhouse condemnations may increase due to excessive airsacculitis.
Case Study
The application of certain live vaccines in the field can cause the appearance of unwanted post-vaccination reactions.
The following company showed respiratory symptoms from 25 of age. The conventional vaccination program of this company against Newcastle disease was based on 4 live vaccines:
Due to the frequent occurrence of post-vaccination respiratory problems, it was decided to carry out a comparative study between two groups of chickens. In the first group, the aforementioned vaccination program was applied and in the second group, in addition to the vaccination program with live ND vaccines, they were vaccinated with Vectormune® ND at day old at the hatchery. Each study group included more than 1 million commercial broilers.
Material and Methods.
To evaluate the effect on tracheal tissue, 15 chickens were randomly chosen from each group at 25 days of age. Healthy birds were selected and none of the flocks showed respiratory symptoms during the previous days.
Complete trachea samples from the larynx to the bifurcation of the bronchi were taken. Histological evaluation ranges from 0 (no inflammatory lesion) to 3 (severe inflammatory lesions). Previously a control necropsy was performed to verify the absence of lesions.
At 43 days of age, slaughter age, a serological HI test study was carried out and an economic evaluation of both groups was analyzed.
Results
The conventional vaccine program birds clearly showed a higher level of inflammatory lesions both in the lower and upper tract of the trachea than in the group of birds also vaccinated with Vectormune® ND.
Regarding serology, only 31% of the birds vaccinated with the conventional program showed protective antibody levels (HI>3), while 100% of the birds vaccinated with Vectormune® ND showed protective levels of antibodies.
Analyzing broiler performances, the Vectormune® ND group showed an improvement in the productive parameters compared to the group vaccinated with the conventional program.
Vectormune® ND group showed an improvement of:
|
Vaccination Program |
Vectormune® ND program |
Conventional Live program |
|
Number of Birds |
1,07 Million Birds |
1,06 Million Birds |
|
% birds of HI test >3 at Day 43 |
100% |
31% |
|
Livability % |
96,3 |
93 |
|
Meat Kg/m² |
54,2 Meat/m² |
53 Meat/m² |
|
European Index |
353 |
332 |
Conclusion