For pigs, we often consider the needs of energy, protein, minerals and vitamins for production and health. When we start thinking about specifically feeding the immune system, we need to look at the unique needs it has, and many key nutrients remain to be identified. We also need to consider the fact that the immune system consists of two different arms: the innate immune system and the adaptive immune system, both with different needs.
The innate immune system provides a first level of defense through physical barriers such as skin, mucosal membranes in the gut, acids in the stomach, as well as specific chemical compounds such as cytokines, acute phase proteins and many others. Mair et al. (2014) provides more complete information on porcine innate immunity.
The innate immune system can prevent and resist certain levels of infection, and typically is sufficient when animals are exposed to small amounts of pathogens; however, at a certain level of exposure, the innate immune system is overwhelmed which leads to a more extensive disease development. During the innate immune response, pigs can have fever, develop disease-induced anorexia, have increased nutrient requirements, and show sickness behavior. For a summary see Sandberg et al. (2007)
A pig acquires immunity when it recognizes a new pathogen that is making it sick. Through a complex process that takes time to develop specific immunity where the pig is capable of producing antibodies specific to the pathogen and enter the final phase of the immune response, and large scale production of antibodies resulting in neutralization of the pathogen. This is referred to as ‘expression of immunity’ where immunological memory has been acquired and varies in time based on the type of pathogen.
For some detailed reviews on the process of acquiring specific immunity to PRRSv (Rahe and Murtaugh, 2017) and the complex interaction between innate and acquired immunity for Influenza virus as described by Crisci et al. (2013).
Diagram of immunity to porcine Influenza from Crisci et al. (2013)
Molecular Immunology Vol 55: pg 204
This is a complex area of immunology, and an even newer area for immune nutrition; the immune system uses a plethora of different nutrients to ensure its correct function, including amino acids, fatty acids, vitamins, minerals, phytonutrients and other yet-to-be-identified compounds. E.g. Wu et al. (2019)
Radzikowska et al (2019) provides a detailed and extensive review of the importance of fatty acid nutrition and the immune system. FURST PROTECT™ and FURST PROTECT DIRECT™ are a critical dietary source of such essential fatty acids.