Formulating Diets for Improved Health Status of Pigs: Current Knowledge and Perspectives

Abstract

Our understanding of nutrition has been evolving to support both performance and immune status of pigs, particularly in disease-challenged animals which experience repartitioning of nutrients from growth towards the immune response. In this sense, it is critical to understand how stress may impact nutrient metabolism and the effects of nutritional interventions able to modulate organ (e.g., gastrointestinal tract) functionality and health. This will be pivotal in the development of effective diet formulation strategies in the context of improved animal performance and health. Therefore, this review will address qualitative and quantitative effects of immune system stimulation on voluntary feed intake and growth performance measurements in pigs. Due to the known repartitioning of nutrients, the effects of stimulating the immune system on nutrient requirements, stratified according to different challenge models, will be explored. Finally, different nutritional strategies (i.e., low protein, amino acid-supplemented diets; functional amino acid supplementation; dietary fiber level and source; diet complexity; organic acids; plant secondary metabolites) will be presented and discussed in the context of their possible role in enhancing the immune response and animal performance.

Keywords: health; immunity; metabolism; nutrition; swine.

Figure 1

Pigs subjected to stimulation of immune system experience increased production of acute-phase proteins (e.g., C-reactive protein, serum amyloid A, haptoglobin, and pig-MAP). Additionally, there is a marked syntheses of endogenous antioxidants to mitigate oxidative stress, including the production of immune-signaling compounds, the release of superoxide dismutase by phagocytic cells and the increased turnover of glutathione, which is a key, non-enzyme antioxidant in the body. Furthermore, a higher concentration of circulating pro-inflammatory cytokines decreases the contractility of gastrointestinal smooth muscle, thereby reducing its motility and sparing energy and nutrient expenditure for digestion. In attempt to minimize metabolic costs, pigs mobilize nutrients, particularly amino acids, from body reserves. This is mediated by proinflammatory cytokines and reactive oxygen species, which stimulate the IκB/NF-κB signaling pathway, eventually activating the ubiquitin proteasome system, and further triggering muscle proteolysis, with the skeletal muscle being the primary source. The reduced feed intake, which is mainly a result of upregulation of feed intake-lowering (anorexigenic) peptides and downregulation of orexigenic peptides, limits the exogenous nutrient supply and aggravates muscle proteolysis.