1 pathogenesis of immunosuppressive diseases in sows
Under normal circumstances, the immune tissues and organs of the body (such as bone marrow, thymus, lymph nodes, spleen, etc.). ), with the participation of immunocompetent cells (such as lymphocytes and mononuclear macrophages). ), which can recognize, respond and remove antigenic substances (pathogens, vaccines) and make the body produce corresponding antibodies. However, when the immune tissues and organs are defective or damaged, immunosuppressive factors will interfere with the presentation of antigens, inhibit or block the formation of immune antibodies, resulting in temporary or permanent immunosuppression, and the body's disease resistance will also decline or even lose.
2 The main harm of immunosuppressive diseases to sows
The harm of immunosuppressive diseases to sows mainly includes:
1) is easy to damage immune organs and systems, interfere with, inhibit or block the presentation of antigens and the formation of antibodies in vivo, weaken or lose the body's barrier protection function, thus causing the body to be infected by pathogenic bacteria, which in turn leads to the obvious decline of the disease resistance of breeding sows and the enhancement of their sensitivity to diseases. In addition, most pathogens are mixed infection, which makes some bacterial diseases that are not harmful to healthy pigs aggravated by the existence of immunosuppressive diseases, resulting in unnecessary economic losses.
2) Physiological metabolism is limited, performance development is affected, and the service life of sows is shortened.
3) Estrus and reproductive disorders, difficult matching, abortion, returning to love, stillbirth, weak fetus, few offspring, serious.
4) Drug resistance decreased and drug resistance increased. Once infected with immunosuppressive diseases, sows are very vulnerable to stress and other infections and invasions: respiratory diseases and digestive tract diseases.
5) The symptoms of genetic diseases are prominent, and the protective power of maternal antibodies is weakened, which is easy to cause piglet infection.
6) Interfering with vaccine immunization and the therapeutic effect of antibiotics, aggravating symptoms and increasing drug costs. Pigs are in the state of immunosuppression, and the direct harm is the failure of vaccine immunization. If the cause and root of immunosuppressive diseases are not found out in time, blindly increasing the immune dose of vaccine will aggravate the damage of immune organs and lead to immune tolerance or immune paralysis. When pigs are latent infected with circovirus or blue ear disease virus, the therapeutic effect of antibiotics will be very poor. At this time, if the dose is blindly increased, it will lead to drug poisoning in pigs, resulting in the decline of liver and kidney function, abortion, stillbirth and even death of sows, which will bring great economic losses to pig farms.
Three causes of immunosuppressive diseases in sows
The main factors causing immunosuppressive diseases in sows can be divided into six major reasons: disease factors, mycotoxins, nutritional factors, stress factors, drug abuse and genetic factors. Among them, porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus type 2 (PCV2), mycoplasma hyopneumoniae (MPS), porcine pseudorabies virus (PRV), classical swine fever virus (CSFV) and mycotoxin are important factors.
3. 1 nutritional factors
Vitamins and trace elements are essential substances for the development of immune organs, lymphocyte differentiation and proliferation, receptor expression and activation, antibody and complement synthesis. If it is insufficient, excessive or improperly matched, it will inevitably induce secondary immunodeficiency.
3.2 Mycotoxin poisoning
Mycotoxin and endotoxin are one of the culprits of all immunosuppressive diseases in pigs. Aflatoxin in mycotoxin can obviously reduce the number of immunoglobulin and T cells in the body, and lead to immunosuppression by causing thymus atrophy and destroying macrophages. Other toxins will also greatly reduce the ability of immune cells to present antigens, which will directly lead to the failure of vaccination, the decline of overall immunity (including specific and non-specific immunity), and the decline of disease resistance. Pigs will be in a sub-health state for a long time, thus inducing mixed infection and secondary infection of various pathogens, leading to illness and even death of animals (clinical manifestations include frequent estrus, ovarian atrophy or swelling, abortion; Piglet diarrhea, pseudorabies and swine flu are frequent; The vulva of suckling pigs is red and swollen; Anorexia in fattening pigs is a sign of mycotoxin poisoning.
3.3 Pressure factors
Under the stress conditions of supercooling, overheating, crowding, weaning, mixing and transportation, pigs will produce abnormal metabolites such as heat stress protein, and at the same time, some hormone levels will increase greatly, thus affecting lymphocyte activity and causing obvious immunosuppression.
3.4 Drug abuse
Long-term abuse of dexamethasone, glucocorticoid, tetracycline and other drugs will lead to immune system damage and immunosuppression.
3.5 Disease factors
Many pathogenic microorganisms can cause obvious immunosuppression, such as PRRSV, porcine circovirus type 2, porcine polycystic virus, PRV and CSFV. The pathogens of these diseases mainly replicate in immune organs and tissues (respiratory mucosa and lymphoid tissues), destroy tissues and organs, or affect the activity of immune cells, interfere with the presentation of antigens, inhibit or block the formation of immune antibodies, and lead to immune interference or immunodeficiency. After PRRSV invades the body, it first replicates in mononuclear macrophages, then transfers to local lymphoid tissues and further spreads to macrophages and monocytes in multiple tissues, causing immune interference or immunosuppression; After GSFV invades the body, it replicates in the tonsils, then transfers to the peripheral lymph nodes, reaches the peripheral blood after local lymph nodes replicate, and proliferates in the spleen, bone marrow, visceral lymph nodes and small intestinal lymph tissues, thus affecting the immune response of animals. PCV2 caused the loss of lymph follicles in the center of lymph follicles and accessory follicles in pigs, and caused apoptosis and the decrease of B and T cells, resulting in decreased immunity. PRV first replicates in nasopharyngeal epithelium and tonsils, and then spreads to nearby lymph nodes with lymph nodes in these positions, thus reducing the immunity of the body. Swine flu virus (SIV) invades the respiratory epithelial cells of infected pigs and proliferates in large numbers, resulting in shedding, necrosis and neutrophil infiltration of lung epithelial cells, thus blocking the respiratory tract and damaging lung tissue. MPS mainly infects respiratory tract and damages cilia and epithelial cells. An important potential factor of mycoplasma pneumonia is the interaction between mycoplasma and lymphocytes. In vitro, mycoplasma membrane is a mitogenic agent of porcine lymphocytes. Mycoplasma infection changed the phagocytic function of alveolar macrophages and suppressed the immunity of pigs. Pigs are prone to secondary Pasteurella multocida pneumonia and Actinobacillus pleuropneumoniae; Actinobacillus pleuropneumoniae (APP) mainly colonizes the respiratory tract of pigs and has high host specificity. Experiments confirmed that APP was colonized in tonsils and adhered to alveolar epithelium, which could be rapidly swallowed or adsorbed by alveolar macrophages and produce toxins, and it was potentially toxic to alveolar macrophages, pulmonary endothelial cells and epithelial cells. Eperythrozoonosis in pigs can cause autoimmune hemolytic anemia. Eperythrozoon interacts with erythrocyte membrane, which breaks or deforms red blood cells, thus destroying the immune mechanism of red blood cells and easily causing infection of other pathogens. It has been proved that during the reproduction of Toxoplasma gondii in the host, a large number of immune cells are destroyed by Toxoplasma gondii, which destroys the immune system of the body and eventually leads to immunosuppression. Escherichia coli toxin produced by Escherichia coli can cause diarrhea in piglets. Virulence factors are mainly absorbed by its fimbriae and settle in the lower intestine, which leads to atrophy of mesenteric lymph nodes, decrease of lymphocytes, destruction of the body's defense mechanism and weakening of immune response, thus making the body in an immunosuppressive state.
4 Comprehensive prevention and control strategies of immunosuppressive diseases in sows
4. 1 control mycotoxins
Aiming at the immunosuppressive diseases of pigs, we must first solve the problem of the disease entering from the mouth. If the mycotoxin problem is not solved, any prevention and control effect is not ideal. Therefore, it is necessary to use good fungicides and biological agents to remove endotoxin and free radicals to reduce the harm of mycotoxins and endotoxin, especially in summer, and pay attention to selecting effective toxin adsorbents to reduce the harm of mycotoxins.
4.2 Scientific feeding management
In order to reduce the occurrence of nutritional deficiency and stress in the above stages, drugs to improve the animal's physique and enhance the animal's disease resistance are added regularly in the feed before and after delivery of pregnant sows and before and after weaning of suckling piglets.
4.3 Establishment of sow defense system
During the whole perinatal period from mating to weaning, it is very important to strengthen the anti-infection ability of sows and prevent viral diseases such as swine fever, blue ear disease, circovirus disease, pseudorabies, parvovirus disease and Japanese encephalitis.
4.4 disinfection
Strengthen disinfection, choose efficient iodine preparation disinfectant, and disinfect regularly. It can effectively kill the internal and external parasites of sows in time and regularly, which has a good effect on sow production performance, piglet growth and survival rate, pig feed conversion rate and so on.
4.5 Scientific medication
Put an end to the abuse of antibiotics and hormones, reduce the occurrence of drug-induced diseases in sows and prolong the service life of sows.
4.6 Regular monitoring
Regularly investigate the etiology and serology of the pig farm, eliminate the problem pigs in time, and purify the breeding pigs by artificial insemination and early weaning.
4.7 Establish a scientific and complete immunization and drug health care program.
According to the results of etiological and serological investigation, special attention should be paid to the immunity of viral diseases. For vaccines that have not achieved definite results, commonly used antibacterial drugs, Chinese and western medicines or microecological preparations for health care and treatment can be added in stages.