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Title:Soy isoflavones and swine health
Author(s):Smith, Brooke Nicole
Director of Research:Dilger, Ryan N
Doctoral Committee Chair(s):Dilger, Ryan N
Doctoral Committee Member(s):Steelman, Andrew J; Lowe, James F; Boler, Dustin
Department / Program:Animal Sciences
Discipline:Animal Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Abstract:Due to increased regulation and mounting consumer concerns, utilization of in-feed antibiotics to promote productivity is declining in modern U.S. livestock production systems. For that reason, there is increased interest and opportunities to identify novel feed additives or value-added feed ingredients that may function as nutritional interventions to improve the health and productivity of our livestock species. Previously, swine nutrition research has found that pigs experiencing high levels of inflammatory stress performed better when fed greater amounts of soybean meal in the diet though it was unclear which component of this soy protein source was conferring these benefits. Among potential components, soy-derived isoflavones show promise as a nutritional intervention against a pathogenic challenge due to their antiviral and anti-inflammatory properties. For swine in particular, there are a number of pathogenic challenges a pig may face throughout its productive life, with immediately post-weaning being a particularly vulnerable phase. A series of three experiments was conducted in order to investigate the effect of dietary soy isoflavones on the growth and immune responses of weaned pigs to a common and pervasive viral pathogen affecting U.S. swine herds, porcine reproductive and respiratory syndrome virus (PRRSV). In the first experiment we sought to determine if soy isoflavones fed at concentrations typically found in standard commercial swine diets would demonstrate protective effects against an acute PRRSV infection in weaned pigs in the presence of two soy protein sources (soy protein concentrate [SPC] and enzyme-treated soybean meal [ETSBM]). While isoflavones minimally impacted growth performance during this acute challenge, they modified the cellular immune response to PRRSV infection by reducing PRRSV-induced band neutrophilia and improving cytotoxic-to-helper T-cell ratios with only a few interactions occurring between soy protein type and isoflavones supplementation across all remaining immune measures collected. These results suggested that isoflavones, regardless of protein source, may influence the activation of adaptive immune system and may facilitate recovery from and clearance of PRRSV infections. To extend those findings, we next sought to determine if soy isoflavones fed at the same level would demonstrate protective effects against both the acute and recovery phases of a PRRSV infection in weaned pigs and if those effects would benefit the growth performance across the entire growth period from weaning to market. Similar to the first experiment, soy isoflavones elicited inconsistent effects on growth performance, but again influenced cellular and global immune responses to PRRSV infection. Isoflavone supplementation increased neutrophil cell counts and the relative proportion of memory T-cells, and decreased the time to full PRRSV clearance from oral fluids. However, the most notable effect isoflavones had in this experiment was reducing pathogen-associated mortality by ~50%, which may have significant economic implications for producers. These findings suggested that isoflavones enable sufficient immune responses needed to reduce mortality in this infection model, but it remained unclear if isoflavones were eliciting these effects directly or if they functioned through an indirect route such as alteration of the gastrointestinal microbiome. For that reason, a third experiment was conducted to evaluate how the ingestion of soy isoflavones in the context of a PRRSV-infection affected the composition of the gastrointestinal microbiome across the entire growth period. Across all time points measured, microbiome analyses indicated that the relative abundance of only a few bacterial populations were directly affected by isoflavones and differences detected were mainly due to PRRSV infection alone. These findings imply that previously observed performance benefits conferred by isoflavones within this PRRSV infection model were not likely due to changes in microbiome composition. Overall, this research demonstrates that isoflavones do not negatively impact the productivity of PRRSV-challenged pigs and may confer additional health benefits through supporting systemic immune responses in the face of a pathogenic challenge, though more research in robust live animal models is merited.
Issue Date:2020-04-27
Rights Information:Copyright 2020 Brooke Smith
Date Available in IDEALS:2020-08-26
Date Deposited:2020-05

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