What Are the Nutritional and Metabolic Costs of Immune System Activation in Pigs?

Optimal lean tissue production can be severely compromised by stress and health challenges in grower-finisher pig production systems. Commonly seen enteric and respiratory pathogen include Porcine Reproductive and Respiratory Syndrome (PRRS) virus, swine dysentery, Porcine Epidemic Diarrhea virus (PEDV), Lawsonia intracellularis, Mycoplasma hyopneumoniae, Salmonella typhimurium and pathogenic E. coli antagonize pig health and performance. Infection with these agents can alter feed efficiency, intestinal function and the economic return for pork producers. Significant advances in molecular and quantitative genetics, clinical diagnostics, microbiology and virology have been made to improve the health in pathogen challenged commercial pigs, but we are still unsure on how to best feed and manage these animals. Collectively, blood metabolite and hormone analyses suggest that there is a major catabolic cost, particularly to skeletal muscle, to support the energetic and protein synthesis needs of immune system response. Additionally, innate and adaptive responses to intense, prolonged or poorly-contained immunological stressors can lead to mitochondrial damage which may impair capacity to generate sufficient ATP for homeostasis, limit energy availability (exacerbated by reduced feed intake) and compromise cell survival and organ function. These changes in bioenergetics link metabolism with inflammation, immune function, cellular and tissue homeostasis and protection. Specific metabolic pathways also affect immune cell differentiation and function, and accordingly have an impact on the overall immune response during health and disease. The metabolic state of immune cells or “immunometabolism” may provide a signature associated with a particular condition or challenge. Therefore, by understanding the metabolic demand of a response to health challenges in pig muscle, liver, immune cells, lungs and intestinal epithelium, we can better develop interventions to modulate the immune system or preserve lean tissue. This paper will discuss the molecular and physiological impact of pathogenic stress challenges on lean tissue accretion, digestibility and immunometabolism in grow-finisher pigs.