Measuring suitability of soybean products for early-weaned pigs with immunological criteria

Two trials were conducted to determine the suitability of soybean products for baby pigs. Weanling pigs (n = 40 and 48 in Trials 1 and 2, respectively) were infused orally (6 g/d) with dried skim milk soybean meal (SBM, 48% CP); soy protein concentrate, moist extruded soy protein concentrate, or soy protein isolate from d 7 to 12 of age. Pigs were then fed a diet containing the same protein source for 1 (Trial 1) or 2 (Trial 2) wk after weaning (d 21 of age). To avoid exposure of pigs to soybean proteins, the dams of pigs were fed a corn-corn gluten meal-based diet supplemented with lysine and tryptophan from d 109 of gestation. All pigs in Trial 1 were killed at 28 d of age, and samples of ileal digesta and small intestine were obtained. In Trial 2, the soy protein isolate was not included, and all pigs were fed a diet containing 4% soybean oil and 1.25% lysine for the last 3 wk of the trial. Growth performance, skin-fold thickness, after intradermal injection of extracts of the corresponding proteins, and anti-soy immunoglobulin G (IgG) titers were measured. Results indicated that pigs fed diets containing SBM had lower (P < .05) villus height and xylose absorption but higher (P < .05) serum anti-soy IgG titers and increased skin-fold thickness compared with the mean of pigs given milk and all other soy treatments. The presence of residual antigenic protein in the digestive tract of pigs fed SBM indicated that conventionally processed, commercial SBM may retain some antigens that cause an immunological response in early-weaned pigs. There were no differences in virus height, crypt depth, antibody titers, and skin-fold thickness between soy protein concentrate and moist extruded soy protein concentrate or soy protein isolate. Pigs fed the diet containing moist extruded soy protein concentrate during the first 14 d postweaning had the highest (P < .05) ADG among pigs fed soy protein sources from d 21 to 35 of age. Moist extrusion processing seemed to improve the utilization of soy protein concentrate compared with soybean meal by baby pigs. Performance of pigs fed moist extruded soy protein concentrate was similar to that of pigs fed a dried skim milk-based diet.