Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically-important disease and ingestion of soy isoflavones (ISF) may benefit PRRSV-infected pigs due to demonstrated anti-inflammatory and anti-viral properties. The objective of this experiment was to recreate immunological effects previously observed in young ymeal.org/?s=Pigs" target="_blank">pigs infected with PRRSV receiving ISF and determine how those effects influence growth performance during the entire growth period from weaning to market. In total, 96 weaned barrows were group-housed in a BSL-2 containment facility and allotted to 1 of 3 experimental treatments that were maintained throughout the study: non-infected pigs received an ISF-devoid control diet (NEG, n=24), and infected pigs received either the control diet (POS, n=36) or that supplemented with total ISF in excess of 1,600 mg/kg (ISF, n=36). Following a 7-day adaptation, weanling pigs were inoculated intranasally with either a sham-control (PBS) or live PRRSV (1×105 TCID50/mL, strain NADC20). After inoculation, individual blood samples (n=8-12/treatment) were routinely collected to monitor viral clearance and hematological parameters, including serum neutralizing anti-PRRSV antibody production. Pen-based oral fluids were used to monitor PRRSV clearance at later growth stages. A 1- or 2-way ANOVA wahref="https://soymeal.org/?s=Pigs" target="_blank">s performed to compare experimental treatments depending on whether the outcome was repeatedly measured. In general, PRRSV infection decreased performance during early growth phases, resulting in 5.4% lower final BW for POS vs. NEG pigs (P < 0.05). Dietary ISF elicited inconsistent effects on growth performance, increased href="https://soymeal.org/?s=Pigs" targrget="_blank">et="_blank"> <a href="https://soymeal.org/?s=Pigs" target="_blank">(/a>>P < 0.05) neutrophil cell counts and the relative proportion of memory T-cells, and decreased (P < 0.05) the time to full PRRSV clearance from oral fluids. Dietary ISF also elicited earlier, more robust anti-PRRSV neutralizing antibody production as compared with POS pigs. Additionally, and most notably, POS pigs experienced ~50% greater infection-related mortality rate vs. ISF pigs (P < 0.05), which may have significant economic implications for producers.
Overall, dietary ISF ingestion supported immune responses and reduced mortality in PRRSV-infected pigs when fed to growing pigs though the biological mechanism of these effects remains unclear.