Effect of Dietary Soy Genistein on Pig Growth and Immune Response during a Viral Challenge
Twelve replications of four littermate pigs from a herd naive for porcine reproductive and respiratory syndrome (PRRS) were weaned (10 ± 2 d of age) and penned individually in disease isolation rooms. Pigs were randomly allotted within litter to one of four dietary concentrations of soy genistein (0, 200, 400, 800 ppm) to quantify the effect of genistein on growth and immune response during a viral challenge. Genistein was provided as the soy glycoside, genistin. At 29 ± 2 d of age (4.9 ± 1.4 kg BW), pigs were oronasally inoculated with 104.3 PRRS virus/mL from strain JA142 in a 2-mL dose. Blood was collected every 4 d from d 0 to 24 postinoculation (PI) and analyzed for serum PPRS virus, interferon (IFN) activity, and alpha-1-acylglycoprotein (AGP) concentrations. Serum virus and IFN peaked at 105 virus/mL and 57% protection, respectively, at 4 d PI and then declined steadily. Serum AGP concentration peaked at 12 d PI. As dietary genistein concentration increased, serum concentrations of PRRS virus decreased linearly (102.46, 102.26, 102.05, 102.14 virus per mL of serum, P < .07) and IFN responded quadratically (28.4, 25.7, 22.8, 30.9% protection, P < .06) independent of d PI. AGP concentrations increased (P < .01) quadratically with the magnitude of the response to dietary genistein maximized at 12 to 16 d PI. Effects of dietary genistein on daily pig gain and feed intake were dependent on dietary genistein concentration and stage of viremia. Daily pig gains from d 0 to 24 postinoculation were improved quadratically (243, 281, 250, 246 g, P < .07) as dietary genistein increased, but the magnitude of the response to dietary genistein concentration lessened as the serum virus concentrations were minimized. Daily feed intakes also were improved quadratically (315, 371, 345, 317 g, P < .05) as genistein concentration increased. These data indicate that dietary soy genistein at 200 to 400 ppm is an orally active immune modulator that enhances systemic serum virus elimination and body growth in virally challenged pigs.