The effects of the viral immunosuppressive diseases PRRS, circovirus disease, and pseudorabies during the finishing stage are reflected more in an “immunosuppressive background” than in independent outbreaks.
PRRS virus mainly attacks alveolar macrophages, directly weakening the lungs’ ability to clear pathogens and greatly lowering the threshold for secondary infections such as Actinobacillus pleuropneumoniae and Pasteurella;
Circovirus 2 causes lymphocyte depletion, resulting in poor vaccine responses and slow growth;
Pseudorabies virus can cause respiratory symptoms and reduced weight gain in finishing pigs, while maintaining a carrier state in the herd. The common consequence of all three is that finishing pigs may appear to have “no serious illness,” yet vaccine antibody levels are inconsistent, illness lasts longer, and cure rates are low.
Porcine reproductive and respiratory syndrome, porcine circovirus disease, and pseudorabies often occur as mixed or secondary infections during the fattening stage, creating a vicious cycle of “viral damage to the immune barrier + secondary bacterial infection.” The consequences include a severe decline in growth performance, an extended time to market, and increased mortality and culling rates.
Prevention and control require “biosecurity as the foundation, targeted vaccination as the support, environmental management as the key, and monitoring and culling.
I. The impacts of the three major diseases during the fattening stage
1. Porcine reproductive and respiratory syndrome (PRRS)
Main signs: Primarily respiratory symptoms, such as coughing, labored breathing, reduced feed intake, and a slight increase in body temperature. The direct mortality rate in finishing pigs is relatively low, but growth performance is severely impaired.
Harm:
Stunted growth: Leads to reduced daily weight gain and generally delays time to market by 7-15 days, or even longer, directly increasing feeding costs.
Immunosuppression: Damages the respiratory mucosa and immune cells, opening the door to secondary infections by bacteria such as Mycoplasma, Actinobacillus pleuropneumoniae, and Glaesserella parasuis, leading to severe respiratory disease syndrome.
On-farm viral reservoirs: Infected pigs can carry and shed the virus for 1-3 months, continuously contaminating the environment and becoming “viral reservoir hosts” in the farm, threatening subsequent batches of pigs.
2. Porcine circovirus disease
Main signs: Finishing pigs that become infected typically show slow growth, a rough, disheveled coat, emaciation, and an increased feed-to-meat ratio. Some develop dermatitis and nephropathy syndrome (skin erythema and scabs).
Hazards:
Severe immunosuppression: Primarily attacks the immune system, causing a widespread decline in the herd’s resistance to PRRS, pseudorabies, and other bacteria, and acting as a “catalyst” for mixed infections.
Declining production performance: Leads to poor herd uniformity, with pigs of uneven sizes and many “runts,” resulting in an overall market weight that falls short of the target and significantly reduced economic returns.
3. Porcine pseudorabies
Main signs: After infection, fattening pigs typically develop persistent dry coughing, rapid breathing, and a slight decrease in feed intake. They often show no typical neurological signs and are easily mistaken for having ordinary Mycoplasma pneumonia.
Harm:
Subclinical infection and shedding: The virus can remain latent in the ganglia and become active, shedding virus during periods of stress. Apparently healthy carrier pigs continuously shed the virus, causing subclinical transmission within the farm.
Increased respiratory burden: In combination with PRRS and Mycoplasma, it damages respiratory cilia, making secondary bacterial infections more difficult to control. Treatment costs are high, and infections tend to recur.
Impaired growth: Slows the growth rate of the pig herd, resulting in runts and increasing the risk of mortality and culling.
II. Comprehensive Prevention and Control Techniques
1. Strengthen biosecurity and husbandry management
All-in/all-out: Strictly implement “all-in/all-out” in the same barn or unit. After the pigs are moved out, thoroughly clean and disinfect the facility, then leave it vacant for more than 7 days to break the cycle of virus transmission between batches.
Environmental control: Maintain appropriate stocking density and improve ventilation to reduce ammonia and dust concentrations and minimize respiratory mucosal damage. Provide adequate warmth and avoid cold or heat stress.
Reduce stress: At key times such as regrouping, changing feed, vaccination, and sudden weather changes, add anti-stress products such as electrolytes and multivitamins and vitamin C to drinking water or feed in advance to stabilize the herd.
2. Develop a scientifically sound immunization program
PRRS: Select the vaccine strain and immunization strategy based on the farm’s infection status (negative, positive and stable, or positive and unstable). Farms with positive status should avoid changing vaccine strains frequently to prevent viral recombination and mutation. The priority is to maintain stable antibody levels in the sow herd and protect piglets.
Porcine circovirus: Administer the first dose to piglets at 14-21 days of age, with a booster at 60-70 days of age. Ensure the vaccination schedule is complete to establish active immune protection.
Pseudorabies: Use a gE gene-deleted vaccine to facilitate differentiation from wild-type virus infection. Administer intranasally to piglets at 1-3 days of age to establish early protection, followed by an intramuscular booster at 35-45 days of age. Vaccinate the breeding herd routinely.
Note: Adjust the vaccination schedule dynamically based on antibody monitoring results from the farm to avoid indiscriminate vaccination.
3. Implement medication-based health management and control of secondary infections
Preventive healthcare: During stressful periods such as regrouping, weaning, and feed changes, or according to the pattern of respiratory disease outbreaks on the farm, add sensitive antibiotics (such as tilmicosin, florfenicol, and doxycycline) together with traditional Chinese medicine (such as remedies for clearing the lungs and resolving phlegm) to the feed for 5-7 days to prevent secondary bacterial infections.
Treatment during illness: For pig groups showing respiratory symptoms, use targeted medication and avoid blindly administering high-dose injections to the entire group. Isolate and treat severely ill individuals, while focusing on preventive care for healthy groups. At the same time, use antipyretic, cough-relieving, and bronchodilating medications to alleviate symptoms.
4. Regularly monitor and cull carrier pigs
Regular testing: Periodically collect samples from grower-finisher pig groups to test antibody and antigen levels for PRRS, circovirus, and pseudorabies, and assess infection status and immunization effectiveness.
Timely culling: Promptly and decisively cull “runts” and sick pigs that are severely growth-retarded, persistently ill, or test positive and shed the pathogen, reducing the viral load and sources of infection on the farm.
Therefore, during the finishing period, the focus of controlling these three diseases is not treatment, but maintaining stable herd immunity and reducing factors that cause immunosuppression. Specifically, this includes ensuring consistent antibody levels from baseline immunization and avoiding missed vaccinations and immunization failures caused by improper procedures; controlling mycotoxins and stress to reduce their secondary impact on the immune system; and, on positive farms, gradually reducing the intensity of pathogen circulation through testing and culling or closed-herd management.