The Immune-System Link to Growth

It’s a recurring scene played out in swine barns across the country — as disease challenges increase, feed efficiency and gains can tumble.

A healthy, robust immune system provides the link to maintaining daily gain as pigs convert feed to pounds. Challenges to the immune system, such as bacteria or viruses, however, can take their toll in reducing feed efficiency as well as overall health status.

By limiting pathogen exposure, and reducing challenges to the immune system, you can maintain or even increase growth rates. “By improving the management of the pathogenic environment and reducing exposure to those pathogens, pigs will grow at a rate closer to their genetic potential,” says Rodney Johnson, animal science professor, University of Illinois.

Keeping your guard up and maintaining high hygiene and biosecurity levels are important components in maintaining feed efficiency objectives. To put it simply, pigs in clean environments will gain more efficiently and more quickly.

“The immune system links the pathogenic environment to growth performance,” Johnson says. “Pathogens stimulate the immune system which, in turn, reduces feed intake and growth.” He notes that pigs maintained in a clean environment are able to accrete protein more quickly than those dealing with environmental challenges.

Bacteria that affect the gut, such as E. coli, Lawsonia intracellularis or Brachyspirahyodysenteriae, pose significant threats to a pig’s immune system and, thereby, feed efficiency. “Pathogens of the gastrointestinal tract often induce diarrhea which significantly affects morphology of the epithelial cell layer, reducing the pig’s ability to absorb nutrients,” Johnson says.

Other pathogens such as porcine reproductive and respiratory syndrome virus also alter metabolism, reducing the pig’s capacity to accrete skeletal muscle protein.

Any infectious pathogen will likely reduce production efficiency under the right circumstances, and it’s common for pigs to encounter multiple infectious microorganisms that can interact.

For example, when PRRS and Mycoplasma combine in a dual attack, the damage is multiplied. When you look at lung lesions, you will see significant interaction between PRRS virus and Mycoplasma hyopneumoniae, Johnson points out. When these two pathogens are present simultaneously, the result is usually much more harmful than either one occurring individually. “The PRRS virus likely reduces the innate immune defenses in the lungs, which allows Mycoplasma to do much more severe damage than it could cause by itself.”

Pathogens are not the only threat to the pig’s immune system. Excess heat or cold, inadequate ventilation, drafts and stress from mixing or overcrowding all take a toll. “These thermal stressors, or secondary environmental pathogenic agents, reduce the pigs’ ability to contend with the primary infectious pathogen,” Johnson says.

Every operation faces unique circumstances and disease threats at various production stages. Identifying where and when your pigs are vulnerable to stressors is the first step in reducing potential exposure to immune-system challenges.

Johnson recommends a comprehensive plan to reduce disease at every step in the process. “Minimizing these secondary pathogenic agents (or stressors) should be part of the comprehensive plan.”

By enforcing controlled access to facilities, eliminating debris, ensuring environmental integrity and practicing careful barn sanitation measures you can reduce pathogen risk. “Most of it comes down to biosecurity and good hygiene,” Johnson says. (See sidebar.)

If pigs get sick, it will open the door to other disease-causing agents that otherwise would not be problematic. Quick treatment is your best course of action. For example, if treatment is delayed for the original illness, chances are that a second infection will occur and complicate recovery substantially. You may be able to reduce disease severity by reducing the likelihood of infection from secondary agents.

When it comes to keeping pigs healthy, there are some dietary tools that can help, points out James Pettigrew, University of Illinois swine nutritionist.

Pettigrew, along with Tung Che, a research colleague, have studied mannan oligosaccharides or MOS — a product made from the cell wall of yeast — and its effect on pigs experimentally infected with PRRS virus. They found that MOS can enhance immune responses in pigs and increase the total number of immune cells such as leukocytes and lymphocytes in the blood. This can help the animal fight not only PRRS but also secondary bacterial co-infections which, in turn, would assist in maintaining feed efficiency.

The researchers found that the product improves growth performance because it redirects nutrients to growth rather than the animal’s immune system. “PRRS virus interferes with the immune response and makes pigs more susceptible to bacterial infections,” Pettigrew says. “This product seems to counteract this effect.”

While MOS may offer benefits, other ingredients can produce the opposite effect. “Be sure you know what ingredients are present in diets,” Johnson says. Certain dietary supplements will help nourish the immune system but also nourish pathogens. Iron is the classic example.

Because iron is important for bacteria production and growth, the pig’s immune system will sequester it to help protect the host. “You cannot just add ingredients to the diet to improve immune-system status without understanding what they do,” Johnson cautions.

Reducing the threat that pathogens pose can be an important step in maintaining your pigs’ growth performance. With careful barn sanitation measures and by reducing environmental challenges, you can provide the link to better feed efficiency.

Infectious diseases developed early on can have chronic effects, and young pigs that face pathogen challenges may never catch up. Strategic sow immunization can reduce disease challenge in piglets by preventing pathogens from entering the environment. Since disease challenges vary among operations, ask your veterinarian what vaccines your sows should receive before farrowing to help ensure a good start for piglets.

Farrowing Room:

Devoting extra time in this area can reduce pre-weaning mortality and benefit pigs throughout the growth period.

“Remove all organic matter by presoaking and then washing with high-pressure, hot water; then disinfect and allow the facility to dry completely,” says Joe Connor, DVM, Carthage Veterinary Service, Carthage, Ill. Allow at least one full night of downtime between farrowing groups.

“Pay particular attention to the difficult-to-access places such as under feeders and mats, as well as the mats themselves,” Connor adds.

Nursery/Grow/Finish:

Because nursery pigs are especially susceptible to enteric diseases, sanitation is critical to maintaining feed efficiency and growth. “Pathogens that pose a significant threat to weaned-pig health include E. coli, Salmonella and Brachyspira hyodysenteriae,” Connor says.

Don’t try to get by with cursory cleaning methods when it comes to the nursery. Connor recommends first soaking and washing floors, ceilings, walls, fans, feeders, waterers and mats to loosen dried manure or caked feed, then thoroughly rinsing with high-pressure, hot water.

Move on to the disinfection step only after all visible debris is removed from all surfaces. Be sure to apply disinfectants labeled for use in swine facilities according to label directions and follow proper dilution rates. Ensure that the disinfectant remains in contact with surfaces for the time specified on the label.

Again, allow time for all disinfected surfaces to dry thoroughly before bringing in the next group of pigs. Be sure to plan for additional drying time in winter and early spring.