It is well documented that when pigs are sick, reduced feed intake occurs. Feed intake in animals is regulated by a complex interaction of brain influences, hormones, sensory and motor pathways, gastro-intestinal tract and other peripheral systems; therefore, the consequence of immune responses to inflammation can have considerable negative impacts on swine performance.

Practitioners continue to explore ways to use a more holistic approach in caring for animals as we find solutions that have not been in our traditional “toolbox,” such as antibiotics and vaccines. The art of practice is blending management technologies with preventive “tools” to reach each farm’s production objectives. But, we have a poor understanding of how to feed sick pigs, especially with pathogens that have prolonged activity in the animal.

Historically, we know products can be found to have immense importance in health. Years ago, small amounts of particular vitamins were found to provide important improvements in human health. As an example, this influenced research into our understanding of selenium and vitamin E as major components for improved health in pig production.

The consequences of an overzealous immune response or even continuous inflammatory response can have considerable negative growth impacts for swine. The goal is to formulate diets with functional feed ingredients that regulate the immune system and reduce inflammation.

Understanding the mechanisms by which the immune system’s changes create or reduce the animal’s performance will allow us to develop management strategies to maximize the pig’s genetic potential and producer profitability. To accomplish this goal, a better understanding of the interactions between nutrition and immunology is needed. Researchers are constantly looking for products that can identify the mechanisms and also promote improved performance but, until consistent results are found, the search continues.

Recently, new data has become available on a second-generation and bioactive fraction derived from mannan oligosaccharides (MOS) (sold as Bio-Mos) of the outer cell wall of a specific strain of yeast. This natural mannan rich fraction of carbohydrate (MRF) (sold as Actigen) has been shown to block unfavorable organisms from the gut. This carbohydrate supports nutrient utilization, maintains digestive function and enzyme activity, controls inflammation and reduces the gap between ideal and actual performance (Che et al., 2011; Samuel et al., 2012; Xiao et al., 2010). These mechanisms are backed by nutrigenomics research.

In particular, MRF has been fed to pigs with interesting outcomes. One aspect of the PRRS virus is that it causes devastating infection in pigs. We know that age continues to be a factor in the variability observed post-infection. In other words, older animals appear to handle the infection better than young animals (Kling et al.: Virology Journal, 2009, 6:177). 

More purified than MOS, MRF provides a great source of attachment for specific pathogens and, because it is not digestible, it potentially “shuttles” attached bacteria through the digestive tract, preventing colonization. In respect to immunomodulation, it has been reported for some time that weanling pigs fed MOS have increased levels of immunoglobulins, increased B-lymphocytes, and enhanced lymphocyte proliferation and phagocytosis of Staphylococcus aureus by macrophages (reviewed by Spring and Privulescu, 1998; Newman, 1994).

MRF most likely does not have a direct effect on the PRRS virus infection when measured by viremia and fever; although, there has been improved growth in infected animals after the first two weeks, i.e., days 14 through 42 after infection, but not during the fever time of 0 through 14 days (Che et al. 2012). 

Economically, we know that tremendous economic impact can be achieved with very small improvements in growth. Thus, the desire is to continue to find products that will help us keep pigs eating when they are sick. In the meantime, products like MRF should be evaluated in farm settings to see if improved performance is achieved.

Editor’s Note: Dr. Tom Gillespie, DVM, Diplomate, ABVP is the owner and founder of Rensselaer Swine Service P.C. He is a past-president of American Association of Swine Veterinarians (AASV) and is a past recipient of the Swine Practitioner of the Year award. Find this article in its entirety at