Utilization of Soy Protein by the Young Pig

Abstract

A series of experiments were conducted to evaluate the limitations of a corn-soy protein diet for providing nutrients to young pigs weaned at three to four weeks of age. Soy protein sources were shown to limit feed efficiency when compared to a milk protein, i.e., casein. Cornstarch reduces feed intake and gain in comparison to lactose in the diet. Removal of the soluble carbohydrate fraction of the soybean was not effective for improving performance beyond that supported by soybean meal. Extrusion cooking of corn and (or) soybeans was found to improve performance of starter pigs over feeding diets based on raw corn, soybean meal and soy oil. Addition of fumaric acid (2 or 3%) improves feed efficiency of pigs fed either a simple, corn-soybean meal diet or a diet supplemented with 25% dried skim milk. Pigs fed corn-based diets supplemented with soy protein concentrate respond more favorably to fumaric acid addition than contemporaries fed a corn-casein diet. Addition of sodium bicarbonate (2.5%) improves performance of pigs fed acidified diets but does not favorably affect the performance of pigs fed diets without fumaric acid.

Evaluation of nutrient digestibility at the ileum showed young pigs digest diets based on casein more effectively than diets containing soy protein sources. Addition of fumaric acid does not improve nutrient digestibility. Fumaric acid addition does not affect gastric emptying rate, digesta pH or pepsin production but reduces organic acid production in gastric cannulated pigs. Supplementation of corn-soybean diets with inorganic acids (HCl, H(,3)PO(,4), and H(,2)SO(,4)) is generally ineffective in promoting improved postweaning performance of starter pigs. Similarly, direct treatment of finely ground soybean meal with H(,3)PO(,4) and (or) NaOH was without effect. It was apparent that addition of some inorganic acids has a deleterious effect on the metabolism of young pigs. Exposure to soy protein for a brief period (days 8 to 10 of life) or daily from day 8 to weaning on day 21 does not affect postweaning performance, antibody titers against soy protein or the cell mediated immune response of pigs to phytohemagglutinin or a soy protein extract. Apparently, the absorption of antibodies from sow colostrum modulates the immune response to dietary proteins in the young pig.