An experiment was conducted to determine whether baby pigs develop hypersensitivity to dietary soybean proteins. Thirty-two pigs were orally infused with either dried skim milk (5 g/d; control) or soybean meal (48% CP; 5 g/d) from d 7 to 14 after birth. Sows were fed a corn-corn gluten meal-based diet supplemented with lysine and tryptophan to avoid exposure of pigs to soybean proteins. Pigs were weaned at 21 d of age and fed diets containing either soybean meal or milk proteins until d 56. One half of the pigs were killed at 28 d of age and the rest at 56 d of age. Segments of small intestine were collected, and intraepithelial lymphocytes were isolated. At 28 d of age, pigs fed diets containing soybean meal had lower (P less than .05) villus height (221 vs 298 microns) and rate of gain (86 vs 204 g/d) than control pigs did. Pigs fed a diet containing soybean meal had higher (P less than .05) immunoglobulin G (IgG) titers to soybean protein than did pigs fed a milk protein-based diet. Blood and intestinal lymphocytes collected on d 28 and 56 did not exhibit any proliferative response when cultured with purified soy proteins (2.5 or 5 microns/ml). Phytohemagglutinin- and pokeweed mitogen-induced lymphocyte proliferations were higher (P less than .05) at d 56 than at d 28, but there were no differences attributable to protein source. There were no differences (P greater than .05) in skin-fold thickness measurements following intradermal injection with soy or milk proteins. Decreased villus height and increased serum IgG titers to soybean proteins coinciding with inferior performance of early weaned pigs fed diets containing soybean meal indicate that conventionally processed, commercial soybean meal may retain some antigens that can cause transient hypersensitivity in piglets.

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 less than .05) villus height and xylose absorption but higher (P less than .05) serum anti-soy IgG titers and increased skin-fold thickness compared with the mean of pigs given milk and all other soy treatments.(ABSTRACT TRUNCATED AT 250 WORDS)