1.Improve the biosecurity system.
The biosecurity system of pig farms is a multi-layered barrier to prevent the invasion of pathogens, and has become an important means of disease prevention and control. Biosecurity is not just about disinfection, it is not the same as disinfection. The perfect biosecurity system is a very complex multidisciplinary system engineering, starting from the planning and construction of the pig farm, throughout all aspects of the production and operation management of the pig farm, the main task is to achieve effective control of the "four flows" (i.e., pig flow, vehicle flow, logistics) and biological media related to production and operation management. Select the site, build and manage the decontamination center, transit area, staff kitchen, and control people, vehicles, objects, pigs and other animals, etc., so as to prevent PRRSV from entering the farmAir filtration system (according to the actual assessment of the pig farm), one-way flow, partition management, isolation and disinfection between various areas, after all the nursery pigs are cleared, the barn is thoroughly cleaned, disinfected and left vacant for more than 1 week, and the stillborn and afterborn are treated harmlessly in a timely manner, and the weak, disabled, secondary, stiff, and sick pigs are decisively disposed of to reduce the viral load in the environment and reduce or avoid bringing the virus in the positive environment to the negative environment. Biosecurity needs to have a well-developed system and must be implemented in place. In reality, there are four main phenomena of imperfect biosecurity: first, biosecurity measures are too cumbersome, employees are resistant, and it is difficult to implement them in place;Second, the biosecurity system is not perfect, there are many loopholes, and there are many opportunities for viruses to take advantage ofThe third is that there is no assessment, just "done", how well it is done, I don't know;Fourth, a biosecurity system has been established, but it has not been implemented due to various reasons. Pig farms need to establish a scientific supervision, assessment and incentive mechanism to ensure the strong execution of pig farm employees, and regularly review and continuously improve the biosecurity system.
2.Prudent use of vaccines is an important tool for the prevention and control of PRRS, but it is also a "double-edged sword", so it is necessary to choose a good vaccine, use the vaccine well, and be cautious in immunization, so as to maximize the positive effect of the vaccine and minimize the negative impact of the vaccine. Now there are many kinds of PRRS vaccines on the market, and all manufacturers are "selling melons", the opinions of different experts are even very different, and the industry is arguing about the harmfulness of live attenuated PRRS vaccines and the effectiveness of inactivated vaccines. If the live attenuated vaccine is used improperly, there may be certain safety risks, especially if the pig farm uses two or more live vaccines at the same time or successively, the use of live vaccines in the late stage of pregnancy, and the high-frequency and high-dose injection of live vaccines, etc., the main risk is that there may be viremia, virulence re-strengthening, detoxification, mutation and recombination of vaccine toxicity and wild poison. However, it is difficult to induce the production of high-level neutralizing antibodies in porcine PRRS inactivated vaccine, which is mainly related to virus preservation, inactivation mode, antigen content, and vaccine adjuvant. It has been shown that vaccine adjuvants also affect the type of immune response by acting on antigen-presenting cells (LAN R.).Tizard, 2012), thus being able to produce a certain amount of neutralizing antibody. The high antigen content of inactivated vaccines can produce a certain amount of neutralizing antibodies, which can also produce a cellular immune response. The immunization effect can be evaluated by the degree of reduction of viral load, the level of N and Gp5+M protein antibodies, the level of CD4+ and CD8+ T cells, the reproductive performance of sows, the stability of piglet production performance, the susceptibility to other secondary diseases and the severity of the disease. Pig farms should formulate scientific immunization procedures and perfect evaluation programs according to the actual situation of the farm, and should not be "led by the nose", let alone change vaccines frequently. There is an ordinary pig farm with 400 sows in Zhejiang, and there has been no African swine fever so far, but PRRS has been unstable. The farm has been using a variety of PRRS vaccines, including commercial vaccines and ** vaccines, highly pathogenic strain vaccines and classic strain vaccines, imported vaccines for sows, and domestic vaccines for commercial pigs. Because it has been unstable, it has been choosing "high-quality" PRRS vaccines.
3.Do a good job of preventive care in the susceptibility stage.
After gilts are in the herd, late gestation, post-weaning and fattening period are the susceptible stages of PRRS (Wang Guoqiang et al., 2022), and any stress such as high temperature and humidity, group transfer, vaccination, cold stimulation and other stresses can easily induce PRRS. Each farm should do preventive health care according to the key time point of susceptibility of the farm. It is also important to choose well (the first choice is high-quality traditional Chinese medicine preparations, followed by macrolide antibiotics such as tilmicosin and tyvancin), and to use (scientific dosage and medication time) preventive health care products (Nalu, 2022). An ordinary pig farm with 400 sows in Zhejiang Province (Figure 2), with 2 small pig farms and 1 slaughterhouse within 2 km, had been negative for PRRS and African swine fever until 2021. There is a characteristic of the field medication: the total amount of health care products such as traditional Chinese medicine extracts, multi-dimensional, live bacteria preparations, yeast accounts for more than two-thirds of the total amount of drugs (including vaccines, chemicals and disinfectants), and the health care program in the late stage of sow gestation and piglet weaning is personally arranged, supervised and strictly implemented by the boss.
3.Scientific feeding management.
PRRSV is also a conditional pathogen. Therefore, the concept of PRRS prevention and control should be changed from the past elimination of pathogens, reliance on vaccines and drugs, and neglect of the health and disease resistance of the pig herd to enhance the quality of the pig herd and control the pathogen. The prevention and control of PRRS in feeding management is mainly to reduce or avoid various environmental stresses and production stresses, control feeding density, provide clean, nutritious and comprehensive diets and clean, sufficient, and suitable temperature drinking water. A pig farm with 2,000 sows in Zhejiang Province pays special attention to anti-stress management and environmental management in addition to strengthening routine feeding management. The amount of anti-stress additives of a certain brand alone reached about 2 million yuan throughout the year, without PRRS vaccine, and rarely used traditional Chinese medicine and macrolide antibiotics to prevent PRRS, and PRRS has been stable in the farm.
4.Effective treatment after onset.
Once PRRS occurs in pig farms, effective measures must be taken to deal with it in a timely manner. The principle of disposal is: try to control the death and minimize the loss;Improve the immunity of the pig herd and prevent secondary infection;Reduces viremia and reduces body damage;Reduce the spread of the disease and shorten the disease cycle;Take comprehensive measures to ensure the stability of the pig herd. The drug control plan is to add 4 kg of high-quality Chinese medicine extract of a certain brand per ton of drinking water, and at the same time, according to the secondary infection, the method of drinking water or injection is adopted, and sensitive antibiotics are used (Du Jihong et al., 2022). After the appetite returns to normal, the drinking water administration can be stopped, and 4 kg of high-quality Chinese medicine extract can be added to each ton of feed for 15 consecutive daysAntibiotics can be discontinued after secondary infection disease control. If the body temperature is particularly high, or the inflammation is particularly severe, 500 grams of flunixin meglumine can be added to each ton of drinking water at the same time for 3 consecutive days. Ensuring that sick pigs receive sufficient amounts of effective drugs is the key to improving the best results. The effect can be assessed by recording the time of negative piglets (PRRS negative PCR), the time to return to normal production (including body temperature and appetite) or reproductive level, and the time when PRRSV is cleared from tissues or blood.