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Why live ND vaccines are NOT the best choice in high ND challenge countries

Introduction

Newcastle disease (ND) is a highly contagious and often severe disease present worldwide that affects multiple species of birds including domestic poultry. Poultry producers in endemic regions to velogenic ND strains face a difficult challenge to keep this persistent field virus away from their commercial operations in spite of overly vaccinated flocks with live ND vaccines.

Live ND vaccines are essential piece of a complete vaccination program but they are not the only option. In high-challenge areas, the application of live and vectorized vaccines is highly effective and safe. 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, reduced flock uniformity, 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 live vaccines in the field can cause the appearance of unwanted post-vaccination reactions.

A broiler producing company showed respiratory symptoms from 25 days of age. The conventional vaccination program of this company against Newcastle disease was based on 4 live vaccines:

  • Two clone LaSota applications via spray at day old and at day 7.
  • Two La Sota applications by drinking water at day 12 and 21.

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 was done using a scoring scale ranging from 0 (no inflammatory lesion) to 3 (severe inflammatory lesions) in an independent laboratory. Previously a control necropsy was performed to verify the absence of lesions.

Score 0 = No inflammatory lesion. Rare Lymphocytes and Plasmocytes. No congestion.
Score 0 = No inflammatory lesion. Rare Lymphocytes and Plasmocytes. No congestion.
Score 1 = Light Inflammatory lesions. Spots of lymphocytes and Plasmocytes. Light congestion.
Score 1 = Light Inflammatory lesions. Spots of lymphocytes and Plasmocytes. Light congestion.
Score 2 = Moderate inflammatory lesions. Lymphocytes and plasmocytes invasion inducing thickening spots around the trachea wall.
Score 2 = Moderate inflammatory lesions. Lymphocytes and plasmocytes invasion inducing thickening spots around the trachea wall.
Score 3 =Severe Inflammatory lesions. Lymphocytes and plasmocytes invasion inducing thickening all around the trachea wall.
Score 3 =Severe Inflammatory lesions. Lymphocytes and plasmocytes invasion inducing thickening all around the trachea wall.

At 43 days of 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 upper and lower tract of the trachea than in the group of birds also vaccinated with Vectormune® ND.

Vectormune® ND program. Average Score: 0.86.
Vectormune® ND program. Average Score: 0.86.
Conventional group. Average Score: 1.86.
Conventional group. Average Score: 1.86.
Vectormune® ND program. Average Score: 0.46.
Vectormune® ND program. Average Score: 0.46.
Conventional program. Average Score: 1.26.
Conventional program. Average Score: 1.26.

Regarding serology, only 31% of the birds vaccinated with the conventional program showed protective antibody levels (HI titre > 3 log2), 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:

  • 21 points in EPEF
  • 3.3% better livability
  • 1.2 Kg more of meat / m2 (54 tons extra meat for 1 million birds)

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

  • Histological analysis of the trachea revealed the negative impact of repeated applications of La Sota vaccine. These Post Vaccination Reactions (PVR) are likely to affect the trachea health and facilitate respiratory outbreaks. This can also be a predisposition factor for any other pathogen leading to complicated respiratory diseases.
  • Vectormune® ND is decreasing the intensity of La Sota vaccine Post vaccination reaction and decreasing the number of respiratory outbreaks.
  • Vectormune® ND also minimizes the ND virus transmission.
  • Vectormune® ND group showed a better immune response level measured with HI tests which is evidencing a more consistent immunization.
  • Vectormune® ND group, showed stronger economical results Livability, European index, Meat kg / m² (parameters requested by the customer).