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Immune System Activation & Performance: “There’s No Free Lunch!” By Jordan Buchan from Southwest Ontario Veterinary Services

When pigs are born their immune systems are not fully functional. In the first few weeks of life they are very dependent on the maternal antibodies and white blood cells that they receive via colostrum and milk. This passive maternally derived protection has a limited duration of protection. The growing pig must develop it’s own active immunity to all sorts of antigens including commensals and pathogens. The pig’s immune system may simply learn to “tolerate” the commensal organism or it may go “full commando” mode in eliminating various pathogens from it’s body. The immune system must also be able to perform this small miracle for a wide variety of antigens at the same time.

During some of the very early experiments with segregated early weaning (SEW) researchers noted that the high health growing pig’s thymus gland was humongous. The thymus gland is a part of the immune system. Conventional health immune challenged pigs have a shrunken thymus gland because the thymus gland is very active in fighting disease in conventional health pigs. The big thymus gland in high health SEW pigs was physical visual evidence that the high health pig was not needing to work its immune system nearly so hard. It takes a lot of body resources to keep your immune system fired up to DEFCON 1 all the time. A benefit of having lower activation of the immune system was that proteins that would have been required to flood the system with immune responses could be diverted to lean growth instead. ( Scheidt et al, 1992)  These French researchers wanted to explore the influence of natural exposure to pathogens on the pig’s immune competence and growth. A field study on 15 commercial farms included 265 piglets that were naturally exposed to various pathogen levels in their environment. Farms and piglets were sorted into low (HSLOW)- and high (HSHIGH)-health status depending on their recurrent exposure to five common swine pathogens.

The researchers found the following:

  1. Monocyte (White Blood Cells), antigen-experienced and cytotoxic lymphocyte subpopulation counts were higher in piglets reared in HSLOW farms as compared to their HSHIGH counterparts
  2. Circulating IFNα (Interferon alpha) level decreased and IgM level increased in all pigs but was greater in HSLOW piglets at any point in time.
  3. LPS-stimulated (Lipopolysaccharide) blood cells derived from HSLOW piglets were more prone to secrete IL-8 than those derived from HSHIGH pigs did. Very active!
  4. Piglets raised under higher pathogen pressure grew less well than HSHIGH piglets and exhibited a different metabolic profile.
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