What to Do When Chicken Immunization Is Ineffective? Cause Analysis and Countermeasures

Now many @#@230@#@ farmers generally report the following problems: (1) The flock is fine when not vaccinated, but as soon as they are vaccinated, the flock breaks out with disease. (2) Sometimes the flock breaks out with disease before they have even been vaccinated. (3) No matter what measures are taken, the immune effect of the vaccine is always poor.

Why do these problems occur? The reason is that the chickens' immune organs have been damaged. After the immune organs of chickens are damaged, the body's resistance to bacterial and viral infections declines, and the flock is very prone to large outbreaks of various epidemic diseases, bringing huge economic losses to the poultry industry. So what are the causes of immune damage? What are the countermeasures?

(1) The influence of immunosuppressive diseases. Immunosuppressive diseases affect the development of the body's immune organs, suppress the cloning and replication of the vaccine within the body, and interfere with antibody production. Infectious bursal disease is a common immunosuppressive disease. For example, after chickens contract infectious bursal disease, it will interfere with the antibodies against Newcastle disease, making them highly susceptible to Newcastle disease infection at this time; therefore, after infectious bursal disease is cured, a Newcastle disease vaccine should be promptly administered as a booster. Infectious proventriculitis, also known as reticuloendotheliosis, is also an immunosuppressive disease. The pathogen of this disease often contaminates live vaccines; after vaccination, the birds become infected with this disease at the same time. Because the symptoms of this disease are mostly atypical and it easily leads to a decline in the body's immunity, secondary diseases (such as colibacillosis, mycoplasmosis and Newcastle disease, etc.) often become difficult to cure because this disease is missed in diagnosis. Therefore, when vaccinating (with live vaccines), in addition to using drugs against vaccine stress reactions (such as roxithromycin, tylosin, ofloxacin), farmers should also add an immune enhancer that does not affect the vaccine titer but has antiviral effects (such as astragalus polysaccharide, etc.) to prevent the occurrence of reticuloendotheliosis.

(2) Unreasonable immunization program design. Chicken farmers always hope to have a foolproof immunization program. Quite a number of farmers pay great attention to learning new techniques; when they see a new immunization program in the literature, they will immunize according to that program. Some farmers go to great lengths to obtain the immunization programs of others from large breeder farms in other provinces and cities, believing that others' immunization programs are perfect and immunizing according to them. This approach is not advisable. The immunization program must be designed in combination with the disease characteristics of the local area and the epidemic situation at the time; only in this way is it most reasonable.

(3) Poor vaccine quality and improper vaccine selection. Poor vaccine quality or unstable quality is a direct cause of immune damage. Factors such as improper transport and storage of vaccines, vaccines being exposed to direct sunlight before immunization, exceeding the usage period, being left out for too long, and not choosing an attenuated vaccine for the first immunization but instead choosing a vaccine of moderately high virulence, or picking the wrong vaccine during immunization, will all cause varying degrees of immune mishandling and failure, leading to disease onset in the body or reduced resistance and infection with other diseases. Therefore, vaccines must be high-efficacy vaccines produced by legitimate manufacturers (for example, avian influenza vaccines must be produced by state-designated manufacturers). At the same time, the transport, storage, selection and use of vaccines must strictly follow the operating procedures.

(4) Proper immunization methods and vaccine dosage. Different immunization methods have different effects after reaching the body. Taking the first immunization as an example, when immunizing against Newcastle disease for the first time, eye dropping and nasal dropping are required. The important purpose of the first immunization is to break through maternal antibodies and stimulate the body to produce basic immunity; the main route of eye dropping and nasal dropping is through the Harderian gland, and immunization can avoid interference from maternal antibodies, while the Harderian gland is behind the eye, so the first immunization against Newcastle disease should use eye dropping and nasal dropping; for infectious bursal disease, oral dropping or drinking water is best; for avian influenza, intramuscular injection is required; for immunization of laying hens in the later stage with strain I vaccine, intramuscular injection is best. It should be noted that when diluting vaccines, it is best to use a dedicated diluent; for eye dropping, nasal dropping, oral dropping or drinking water, it is best to dilute with cooled boiled water before use. It is prohibited for the diluent to contain disinfectants or to use metal containers to hold the diluted vaccine, otherwise immunization failure or immune damage will occur. Now many chicken farmers believe that the larger the vaccine dose, the better, which is also wrong. If the vaccine dose is too small or not used for a long time, the immune effect cannot be achieved; if the vaccine dose is too large or the number of immunizations is too frequent, it can cause paralysis of the immune organs, so the vaccine is not better the larger the dose. Taking Newcastle disease as an example: during the laying period, it is best to administer 4-5 times the dose of C030 or strain IV vaccine in drinking water every one to one and a half months, while adding some immune enhancers (such as astragalus polysaccharide).

(5) Interference between vaccines. When two or more vaccines without cross-reaction are vaccinated at the same time, the immune response to one of the vaccines often declines, affecting the immune effect, such as Newcastle disease and infectious bursal disease, infectious laryngotracheitis and Newcastle disease, etc. If the immunization times of the two are scheduled very close together, it will lead to immunization failure; therefore, the immunization interval between the two should be at least seven days.

(6) Reasons related to feeding and management. Stress factors such as the environment being too cold or too hot, high humidity, poor ventilation, crowding, sudden feed changes, moving groups, and beak trimming will all lead to increased secretion of adrenal cortex hormones in the body, and adrenal cortex hormones can significantly damage lymphocytes, have an inhibitory effect on macrophages, and increase the catabolism of immunoglobulins. Therefore, before and after immunization, the stress on the flock should be minimized as much as possible, while adding some immune enhancers. Vitamins, trace elements and complete proteins can all affect the body's immune response to antigens. For example, amino acids can increase the content of immunoglobulins. It has been reported that adding a certain amount of arginine to the feed has a clear promoting effect on the growth of lymphoid organs in chickens and can effectively improve the immune response; on the contrary, a lack of arginine will reduce the weight of immune organs and cause immune damage. In addition, a lack of vitamin A can cause premature atrophy of the bursa of Fabricius and a decline in resistance. Therefore, various nutrients should be supplemented regularly to ensure the normal development of immune organs. There is also the issue that routine disinfection is not thorough, and there are large amounts of pathogenic bacteria in the surrounding environment, so the flock is in a sub-healthy state during the period of vaccine use. Especially during the summer plum rain period, the moisture content in the feed exceeds the standard, and sometimes when too much feed is mixed, it will inevitably become moldy; aflatoxin causes atrophy of the body's immune organs (such as the bursa of Fabricius and thymus, etc.), all of which can lead to damage to the immune system, thus causing immunization failure. Therefore, routine disinfection and elimination of sources of infection should be strengthened, feed mold should be prevented, and the flock should be kept in a healthy state during immunization, thereby improving the immune effect, preventing the occurrence of disease, and increasing the benefits of chicken farming.