The causes of swine respiratory disease are complex, and no single prevention and control measure can be effective
Don't count on a single control measure: the causes of swine respiratory disease are complex
In the process of pig production, swine respiratory disease is often the result of the interaction of multiple factors (viruses, bacteria, Mycoplasma hyopneumoniae, poor feeding and management conditions, etc.), so it is often called "swine respiratory disease complex." Pig farms often plant a "bomb" due to the absence of biosecurity measures or the purchase of subclinically infected pigs without strict quarantine, and the "bomb" is detonated by poor feeding and management or malnutrition.
Epidemiological overview
Because coughing and sneezing by sick pigs can discharge pathogens with respiratory secretions into the surrounding environment, which then infect other healthy pigs through the respiratory tract, if effectiveprevention and controlmeasures are not taken, pigs of any breed, age or sex can develop the disease. However, outbreaks occur mostly in nursery pigs aged 6 to 10 weeks and growing-finishing pigs aged 13 to 20 weeks, with a morbidity rate generally of 30 to 65% and a mortality rate of 15 to 85%; the younger the pig, the higher the mortality rate, and the response is even more severe when rearing conditions are poor.
Main causes of respiratory disease
1. Infectious factors
(1) Viruses: porcine reproductive and respiratory syndrome virus, swine influenza virus, classical swine fever virus, pseudorabies virus, circovirus, porcine respiratory coronavirus, etc.
(2) Bacteria: mainly Streptococcus, Haemophilus parasuis, Bordetella bronchiseptica, Pasteurella multocida, Actinobacillus pleuropneumoniae, etc.
(3) Mycoplasma: Mycoplasma hyopneumoniae, etc.
(4) Parasites: Toxoplasma gondii in pigs, Ascaris suum, etc.
(5) Others: Eperythrozoon suis, etc.
Many pathogens (such as Mycoplasma hyopneumoniae, porcine reproductive and respiratory syndrome virus, swine influenza virus, classical swine fever virus, pseudorabies virus, circovirus, porcine respiratory coronavirus, Bordetella bronchiseptica, etc.) can directly destroy the pig's respiratory defense system, causing damage to and failure of the respiratory immune system, thereby losing its ability to clear airborne foreign matter (including pathogenic microorganisms, harmful particles and metabolic products of the body). This makes infection by other pathogens (such as Streptococcus suis, Haemophilus parasuis, Pasteurella, Actinobacillus pleuropneumoniae, etc.) much easier, and the clinical manifestations and harm are significantly exacerbated.
2. Non-infectious factors
Non-infectious factors are mainly feeding and management conditions, chiefly: nutritional level, stocking density, air quality, dust, temperature, humidity, frequency of group movement, mycotoxins, and unreasonable vaccination and antibiotic use, as well as recklessly mixing pigs from different sources or with large age differences in the same group and continuous production in the barns. These are often the triggers for outbreaks of swine respiratory disease.
3. Combined factors
In fact, the above causes are not isolated; they often promote each other and are mutually causal. This makes the causes of swine respiratory disease extremely complex, which is also why swine respiratory disease is difficult to diagnose andprevent and control.
Clinical symptoms of swine respiratory disease
In the early stage, sick pigs mainly show a dry cough and panting, especially obvious in the early morning when the herd is suddenly startled or when the keeper drives the pigs; their body temperature is generally normal, and appetite and spirit show little change, so it is easily overlooked.
As the disease progresses, sick pigs may stand dull, arch their backs, stretch their necks, and droop their heads, with severe coughing or spasmodic paroxysmal coughing, obvious abdominal breathing, and in severe cases protruding eyeballs and cyanosis of the visible mucous membranes or extremities. Acute cases are often accompanied by varying degrees of fever and often die suddenly due to extreme respiratory difficulty or stress; most pigs go from acute cases to subacute or chronic cases after being handled by "experience," with affected pigs showing progressive emaciation, enlarged superficial lymph nodes, severe immune side effects, and failure of diagnostic and treatment experience. If rearing conditions are poor, density is high, adverse stress is frequent, and handling measures are chaotic, the morbidity, mortality and clinical manifestations are even more severe.
Main lesions of swine respiratory disease
All sick pigs show varying degrees of pneumonia. Necropsy of nursery pigs aged 6 to 10 weeks shows diffuse interstitial pneumonia and widespread enlargement of lymph nodes, pulmonary hemorrhage, consolidation (rubbery lungs that cannot shrink) and mottled lesions (grayish-white necrosis alternating with brown hemorrhagic patches), with purulent foci in individual lungs; the lungs of sick pigs show varying degrees of mixed infection, some sick pigs have widespread polyserositis (much fibrin exudation in the thoracic and abdominal cavities, even causing adhesions), and some lung lesions resemble those of Mycoplasma hyopneumoniae pneumonia.
In addition to lung lesions, some sick pigs also show bleeding from the nostrils or blood-tinged foam, laryngeal hemorrhage and edema, enlarged and hemorrhagic tonsils, enlarged and hemorrhagic lymph nodes in multiple sites, and increased mucus or foam in the trachea, sometimes blood-tinged.
Comprehensive prevention and control of swine respiratory disease
Because the causes of swine respiratory disease are complex, one cannot expect a single measure to eliminate the disease. Taking comprehensive measures and treating symptoms according to the specific situation of the affected herd may achieve a "twice the result with half the effort":
1. Adhere to self-breeding and self-raising; if introduction of breeding stock is needed, strict quarantine should be carried out. Isolate and observe for at least 1 month before merging into the herd, and try to avoid recklessly mixing pigs from different sources or with large age differences in the same group.
2. Strengthen feeding and management. Avoid feed mildew, drafts, and adverse stress such as frequent group movement/mixing/feed changes/injections, reduce dust, maintain reasonable stocking density, provide balanced feed nutrition, and do a good job in cleaning, sanitation and environmental disinfection.
3. Severe environmental pollution, poor feed and drinking water safety, high infection pressure from various pathogens (including vaccine-strain pathogens), malnutrition, frequent stress and many other factors make the herd's constitution like that of an old ox, unable to bear the burden, and the pig's immune system is often in a "hand-to-hand combat" of overload operation, so that the immune system is damaged or paralyzed, resulting in immune failure. In order to reduce immune side effects and improve the effect of vaccine immunization, it is quite necessary to adopt "internal disinfection" and "short-term superior feeding" measures for pigs in a "sub-healthy" state before vaccination.
(1) Internal disinfection: Based on the clinical manifestations of the herd and past medication records, carry out reasonable preventive medication and health care, solve the "pig unnamed high fever" in pig production, and at the same time effectively free up immune space and reduce the interference of unfavorable factors such as wild bacterial/viral strains, mycotoxins and adverse stress on specific immunization. In short, we should let the pig immune system operate in an orderly manner as much as possible, reduce the burden on the immune system, and prevent "overload" operation.
(2) Short-term superior feeding: When the animal body is under stress or the immune system is stimulated by foreign matter (such as pathogenic microorganisms, mycotoxins and other non-self substances), it will immediately mobilize all resources for self-protection. Amino acids, vitamins, electrolytes, oligosaccharides, etc. are the basic nutrients for body metabolism. If they are not supplemented promptly and effectively, the body will inevitably suffer damage due to "running out of ammunition and supplies," and its immunity and anti-stress ability will also be greatly weakened, thus forming a vicious cycle.
4. According to the epidemic situation in one's own pig farm and surrounding areas, select safe and efficient vaccines in a targeted manner, and formulate and implement a reasonable immunization program, especially ensuring that sows maintain a good specific immune protection state to provide protection for the health of piglets. This is even more true for porcine reproductive and respiratory syndrome-positive pig farms, which should adopt a "dancing with the blue" mindset and conscientiously implement all measures conducive to improving the pig's constitution. That is, all measures conducive to improving the pig's constitution are necessary to implement, and do not do to pigs what pigs would not want done to themselves.
5. It is quite necessary to formulate and implement preventive medication and health care for sows before and after farrowing and for pigs before and after adverse stress such as birth, castration, weaning, group movement, mixing, feed change, vaccination, transport, and sudden weather changes.