Analysis of the Causes of Immune Failure in Chicken Farms and Prevention and Control Measures

In Xinye County in recent years, the @#@230@#@ industry has gained strong momentum, with small and medium-sized chicken farms springing up like bamboo shoots after rain, flourishing vigorously. With the rapid increase of the breeding industry, how to do a good job in flock immunization has become urgent. Most farmers can also recognize the importance of epidemic prevention work, but due to various reasons, the immunization effect is uncertain and efforts are wasted, with economic benefits declining significantly. Based on many years of practical experience, the author puts forward some preliminary views on the causes of immune failure in chicken farms, for the reference of fellow breeders.

1 Causes of immune failure

1.1 Interference of maternal antibodies in chicks In recent years, due to the widespread use of various vaccines in breeding poultry, the level of maternal antibodies in chicks has increased significantly. If vaccination is carried out when the maternal antibody level is relatively high, the vaccine antigen will be neutralized by maternal antibodies at this time, so that it cannot proliferate in the body, leading to immune failure, and it also reduces the level of maternal antibodies, thereby increasing the susceptibility of chicks. Once a virulent strain invades, disease may occur.

1.2 Vaccine quality problems The quality of vaccines should meet standards. The key to attenuated vaccines is vitality, and the key to live vaccines is effective content. Attention should also be paid to the transportation, storage and expiry date of vaccines, otherwise it may cause a reduction in vaccine vitality and titer, leading to immune failure.

1.3 Inappropriate inoculation methods Various vaccines have certain inoculation methods, such as eye drop, drinking water, aerosol, injection, wing web stab, etc. Fowl pox vaccine should be inoculated by the wing web stab method; if drinking water or eye drop methods are used, the due effect cannot be achieved.

1.4 Operational errors during vaccination The vaccine diluent contains substances that damage the vaccine (iron, chloride ions, disinfectants, etc.) or antibacterial drugs are added, and the dilution concentration is arbitrarily increased or decreased, causing excess or insufficient vaccine; when diluting the vaccine, time and place are not paid attention to, and it is carried out in sunlight all day, causing the vaccine to become ineffective under high temperature; during drinking water immunization, the vaccine cannot be consumed within the specified time or the drinking is uneven. For example, the diluent for Marek's disease vaccine must be injected within 1-2 hours; vaccinating chicks with the remaining vaccine will result in immune failure.

1.5 Improper combined use of vaccines Some vaccines can be used in combination, while others may interfere with each other. If the combination is improper or the interval between two vaccinations is too short, immune failure may also occur. For example, fowl pox vaccine and Newcastle disease vaccine interfere with each other, and infectious bronchitis virus has an interfering effect on Newcastle disease virus.

1.6 Interference of infectious diseases Infectious bursal disease virus can kill B lymphocytes in the bursa of Fabricius, causing obstacles in antibody production. Therefore, after the occurrence of bursal disease, immune failure of other diseases is often caused.

1.7 Infection by pathogens during the immune blank period Any vaccine requires time from inoculation to the production of immunity in the chicken body. This period is called the immune blank period. If infection occurs during the blank period, disease will still occur.

1.8 Unreasonable immunization procedures Different flocks also have inconsistent antibody levels. Immunization times vary from earlier to later, and different types of vaccines also differ in immunization methods. This requires the establishment of reasonable immunization procedures. Unreasonable immunization procedures can easily lead to immune failure.

2.1 Formulate reasonable and feasible immunization procedures Due to different local conditions (epidemic situation, chicken breeds, source of chicks, etc.), it is impossible to have an unchanging immunization procedure. Therefore, each chicken farm should formulate an immunization procedure suitable for its actual situation according to the epidemic situation of chicken diseases and local epidemics, combined with the growth and decline patterns of antibodies produced by various vaccines (conducting immune antibody monitoring). For example, for Newcastle disease basic immunization, if the chicks come from a regular breeding chicken farm, but many native chickens and local chickens come from free-range households and farmers, and are not necessarily from the same farm owner, the maternal antibodies of the chicks are very low or even absent. In this case, basic immunization against Newcastle disease should be carried out on the 1st day.

2.2 Reduce stress responses During the process of vaccine immunization, various stress responses should be minimized as much as possible, and it is not advisable to carry out beak trimming, flock transfer, feed change and other work at the same time. After vaccination, feeding management should also be strengthened. Adverse factors such as too high or too low temperature in the chicken house, overcrowding of the flock, and poor ventilation will inhibit the body's humoral immunity and cellular immunity, leading to a decrease in the protective power of the vaccine. In order to reduce the stress response of the flock during vaccination, vitamin C, vitamin K or immune enhancers can be added to drinking water 2-3 days before and after vaccination, or anti-stress drugs such as reserpine and chlorpromazine can be added to the feed.

2.3 Adopt correct immunization operation methods and inoculation routes Commonly used inoculation methods include intranasal and eye drop methods, drinking water immunization and injection. Inoculation should be carried out according to the prescribed methods and should not be changed arbitrarily. ① Eye drop and nasal drop method. This is a commonly used immunization method for chicks. When immunizing by this method, be sure to see that the vaccine has completely entered the eye or nose before releasing your hand. Do not release immediately after dropping, so as to prevent the vaccine from flowing out of the eye or nose and affecting the immunization effect. ② Drinking water immunization. It is best to use deep well water; tap water should be left to stand overnight before use; drinking water equipment must be cleaned thoroughly; the vaccine dosage should not be excessively increased, otherwise it will cause strong stress and affect the immunization effect. The amount of water used to dilute the vaccine should be appropriate, and it is best for the chickens to finish drinking within 30 minutes. ③ Injection method. Both the injection method and the diluent should be used according to the instructions. Marek's vaccine must use the special diluent provided by the manufacturer, while general vaccines are diluted with sterile water for injection.

2.4 Implement comprehensive prevention and control measures The effect after vaccination also depends on whether the function of the chicken body's immune system is normal. Therefore, for diseases that damage immune organs, such as infectious bursal disease of chickens, prevention must be done well. At the same time, feed mildew should also be prevented, because the mycotoxins contained in moldy feed will destroy the normal function of the immune system and form severe immunosuppression. In addition, because it takes about 7 days for attenuated vaccines and about 15 days for oil-emulsion inactivated vaccines to produce strong immunity, and different vaccine antigens differ somewhat, do not be negligent after vaccination. Isolation and disinfection work should be strengthened, and the immunized flock should be isolated and raised for more than 15 days. At the same time, personnel entering and leaving the chicken house must be strictly disinfected, and outsiders are prohibited from entering the chicken house.

2.5 Adopt an all-in-all-out system Try to achieve all-in-all-out as much as possible. After each batch of chickens is sold, a comprehensive and thorough cleaning and disinfection should be carried out to eliminate the retention and spread of pathogens.