1 The characteristics of chronic swine fever. The piglet mortality rate is higher than that of the big pig. The sick pig mainly shows digestive tract symptoms. In the absence of secondary infection, the body temperature is generally normal, the feed intake is significantly reduced, and the patient with a slightly longer course is drooling and diarrhea. Progressive weight loss, late failure and death. Poisoned sows can infect piglets through the placenta. There are abortions, stillbirths, fetal malformations, mummified weak ones, or some healthy piglets. When the sow is mated, it is often infertile. Sometimes the pig does not show symptoms or secondary infection with other pathogens to cover up its symptoms. Anatomical lesions are mainly manifested in large areas of gastric mucosa shedding, congestion. The kidneys are not swollen, showing a yellowish color, a small amount of bleeding on the surface of the kidney, blood thin as water. The flow is rarely solidified on the ground. The lymph nodes appear congested and swollen. The four sides of the face are bleeding. The red and white marbles, the ileocecal valve, the colon and the ileum form a "button-like swelling", and the boar's foreskin accumulates urine. The pathological changes of other organs are not significant.
2 Analysis of immune failure and subclinical infection
2.1 Affected by mycotoxins Mycotoxins have a destructive effect on the immune system. The immune system of pigs is not enough to inhibit the invasion of pathogens. It creates favorable conditions for the occurrence of diseases. Mycotoxins can cause immunosuppression in pigs and cause immune failure. For example, aflatoxin B. And the neomycin-derived T-mycin inhibits protein synthesis and cell proliferation. Mycotoxins act on lymphocyte membranes in vitro or interfere with macromolecular synthesis and its function. For example, cytochalasin is highly cytotoxic to lymphocytes and acts on cytokinesis, thereby inhibiting immune function.
2.2 The impact of immunosuppressive diseases Infectious diseases are the main cause of the suppression of immunity of livestock and poultry. The occurrence of some infectious diseases may increase the susceptibility of animals to other pathogens. The immune response to various vaccines will decline, and even lead to immunity. failure. Some viruses directly invade the lymphoid organs and immune cells of pigs. Inducing the release of certain cytokines activates inhibitory cells, thereby affecting the immune effect. In production, when other infectious diseases occur, it is impossible to immunize pigs.
2.3 Innate immune tolerance The immune failure caused by persistent infection of sows and placental infection in piglets. Piglets that survive after birthplace infection are often persistent infections, which can be poisoned and detoxified for a long time. They do not manifest clinical symptoms. In addition to causing a vicious circle in the pig farm, the viremia can be transiently reduced within a few days by colostrum after birth, but the virus can not be established in the whole body epithelial tissue, lymphoid tissue and reticuloendothelial tissue. Sexual antibody response. Forms immune tolerance. It does not produce an immune response to vaccine immunization, thus failing to form vaccine antibody protection ability. Once intensive, it can cause disease.
2.4 Quality of vaccines Improper transport, storage and use of vaccines can affect the quality of vaccines. The frozen and dried piglets should be transported and stored under low temperature conditions. If the diluted vaccine cannot be used once, it can be temporarily stored in ice bottles or refrigerated at low temperature. In addition, mistakes in the operation process, such as the use of a vacuum-free vaccine or vaccine over the expiration date, the injection is not strict, resulting in the spread of latent virus, etc., will affect the immune effect of the vaccine. On the other hand, unscrupulous manufacturers privately manufacture some swine fever vaccines with unqualified quality, and the quality of veterinary practitioners is generally low, which increases the number of pigs with immune failure and hidden piglets.
2.5 Immunization procedures The key to irrational immunization procedures is to exclude maternal antibody interference. Determine a reasonable first-day age. Some pig farms ignore the actual situation of the farm and the individual differences of pigs. The same immunization program is used for immunization. If the maternal antibody titer is still high, the vaccine will be neutralized and partially attenuated by the maternal antibody. Attenuated replication. Piglets cannot produce strong active immunity.
2.6 Vaccine Immunization Insufficient For those clinically infected pigs that are in a semi-immune state, if only one live swine fever vaccine is given at this time, not only can it not produce immunity, but it will stimulate chronic swine fever.
2.7 Maternal antibody interference The maternal antibody has an immune effect on the born piglets. That is, the duality of the maternal antibody. Therefore, when using high-quality vaccines for piglets, the titer of maternal antibodies should be considered before immunization. At the same time, attention should be paid to the uniformity of maternal antibodies by measuring maternal antibody titers before immunization. Degree, adjust the uniformity of maternal antibodies.
2.8 Vaccine production can't keep up with its mutations This may be the root cause of immune failure. The domestic swine fever virus strain has changed, and the original vaccine is still used in each farm. According to reports, the strain rate of swine fever virus has reached 74%.
2.9 Disadvantaged control of transmission routes It is currently believed that the main routes of transmission of piglets include vehicles, pens, feed and clothing, while flies, birds and human activities also play an important role in mechanical transmission. These did not attract enough attention.
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3 Prevention and control measures
3.1 Strengthen the immune surveillance of swine fever. Develop a reasonable immunization program to regularly monitor the immune antibody of swine fever. Understand the antibody level of the swine and the immune effect after the swine fever vaccine, and use this as a basis to scientifically and rationally formulate the immunization program. Sow immunization should avoid breeding and pregnancy. In order to avoid placental infection or pre-immunization, piglets develop anaphylactic shock. The immunization program described below can be used for reference in pig farms: sows are immunized with swine fever 2 to 25 days postpartum. Boars are immunized once every spring and fall. Each pig uses six piglets. The piglets were first exempted on the 20th and the second was exempted at 60 days of age. The following immunization procedures are referred to pig farms that have been swine or threatened. In order to prevent early infection of piglets, the newborn piglets can be pre-immunized. Before the piglets are colostrum, one pig or two piglets are injected with attenuated vaccine. Each piglet is given colostrum after 2 hours of injection. At the age of 35 days, two exemptions were given at the age of 70 days.
3.2 Pay attention to the management of vaccines. Pig farms should choose vaccines produced by regular manufacturers. They should be transported, stored and used in strict accordance with the regulations. They should be used immediately after dilution. They should not be stored for too long. If the diluted vaccine cannot be used up at one time, it should be put. Store at low temperature in an ice or freezer.
3.3 Pay attention to the damage of mycotoxins. Prevention and control of molds When taking care of mold and adding mycotoxin treatment or raw materials, we should try to understand the source, harvest, processing and transportation conditions of the feed. Try to purchase fresh raw materials with good moisture content. In view of the fact that the mycotoxin content in the feed is seriously exceeded, the farm should add a mycotoxin treatment agent to the slightly mildewed feed, and the serious and moderately mildewed feed must be completely discarded. Because there are many types of mycotoxins, when a mycotoxin treatment agent is selected, it is necessary to consider a broad-spectrum, highly adsorbable mycotoxin treatment agent that can improve the immunity of the body and promote the recovery of the damaged body.
3.4 Control of other infectious diseases. In particular, immunosuppressive disease control Other non-swine fever infectious diseases are the basis of comprehensive prevention and control technology for swine fever. In recent years, the immunosuppressive diseases of pigs such as porcine reproductive and respiratory syndrome, circovirus, and pseudorabies have been on the rise, causing different degrees of immune failure in pigs, leading to immune failure of swine fever. The farm should adopt a sound immunization program, improve feeding management, improve the ecological environment, and prevent and control immunosuppressive diseases.
3.5 Purification of reserve pigs and breeding herds This work is an important means to prevent reproductive disorders and vicious cycles. It eliminates persistent infection of poisoned pigs, fosters healthy levels of pigs, and completely eliminates hidden dangers from the inside, forming a powerful Security backing.
3.6 Reasonable use of antibiotics Antibiotics are not effective against viruses. They can control or treat bacterial hazards to prevent or reduce secondary infections in pigs. A good effect drug such as amoxicillin is added to the feed one week before weaning and four weeks after weaning.
3.7 Regular disinfection In the absence of disease, large-scale pig farms should be disinfected 1 or 2 times a week. When an epidemic occurs, it should be disinfected 1 or 2 times a day. At the same time, disinfectants should be replaced frequently.
3.8 Strengthening the management of feeding and keeping warm in the winter, and doing the heatstroke prevention and cooling work in the summer, so that the pig has only a comfortable living environment.
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