In actual poultry farming, we often hear farmers ask questions like this: “My chicken farm is fine when I don’t vaccinate, but it’s bound to get sick as soon as I vaccinate! Why do chickens still get sick after immunization with oil-based vaccines and freeze-dried vaccines? How can illness after vaccination be avoided?” These questions trouble not only poultry farmers, but also veterinarians who serve the livestock industry. Why do these problems occur? How can they be prevented? This is highly important for guiding practical livestock production correctly.
I. Why do chicks have stress reactions after their first live vaccine dose?
When chicks receive their first Newcastle disease and infectious bursal disease vaccinations at 7 and 14 days of age, respiratory symptoms often occur. Similar symptoms can also occur in layer flocks after live vaccine vaccination. Newcastle disease is vaccinated against most frequently, yet even when live and inactivated vaccines are administered together, atypical Newcastle disease still often occurs. Influenza vaccination is given 3—4 times before the birds start laying, but seasonal influenza outbreaks still occur regularly in actual production. When chicks receive a new live vaccine for the first time, they are encountering the virus for the first time too, so the stress reaction may be greater. With a repeat vaccination, the stress reaction is relatively milder. However, maternal antibody levels must also be considered. If maternal antibody levels are high and uniform, they can resist the immune response, resulting in less vaccination stress. But if maternal antibody levels are too high, the vaccine may be neutralized by maternal antibodies, preventing it from generating a sufficient protection rate.
II. Why is influenza so difficult to prevent?
In actual production, influenza viruses mutate much faster than new vaccines can be developed. A mismatch between circulating strains and vaccine strains may be the main reason influenza can occur despite vaccination. To ensure the health of the flock, in actual production it is essential to take local circulating strains into account, choose an autogenous vaccine suited to the chicken farm, and combine it with a reasonable vaccination program. A scientific vaccination program must be developed based on local disease incidence, the farm’s farming standards, the farming season, and disease incidence. What is suitable is best.
III. The flock’s health before vaccination is critical:
Vaccination is a preventive measure that provides healthy flocks with artificial active immunity. If the flock is already in a suboptimal health condition before vaccination, vaccination may accelerate the onset of illness, resulting in a situation where the flock is fine without vaccination but gets sick as soon as it is vaccinated. We must also recognize that pollution in the surrounding farming environment deserves attention. If wild viruses are present in the environment, they may take advantage of the flock’s weakened immunity following stress and invade, further aggravating illness after vaccination.
IV. Scientific Antibody Testing
After vaccination, antibody levels must be monitored scientifically and regularly to determine whether immunization has been successful and to ensure that the flock has high, long-lasting antibody levels during the laying period. This also helps determine when the next immunization is appropriate. Monitor antibody levels in the flock, paying particular attention to chicks during the immunization gap (around 4 weeks), at around 25 weeks, and at 50-60 weeks. Do not take this lightly!
V. Create the Most Comfortable Possible Living Environment for the Flock
Ensure that the flock remains in good health. The flock’s health status determines the severity of its stress response after immunization. Ventilation management in the poultry house is of utmost importance. Set temperature and humidity according to the chickens’ age-specific needs. Also, make every effort to reduce various sources of stress. For example, avoid immunizing high-producing flocks at around 170 days of age, as far as possible, to ensure high and stable production and thereby improve economic benefits.