Utilization of Soybean Protein by Baby Pigs and by Rats

Abstract

Studies with young pigs and rats to evaluate the effect of proteolytic enzymes, amino acids and age on utilization of isolated soybean protein are reported. Pepsin and/or trypsin added to a basal soybean-protein diet had no effect on baby pig growth, feed efficiency, or protein digestibility. DL-methionine added to the same basal diet at levels of 0.23 and 0.45% to provide a total of 0.68 and 0.90% methionine-cystine increased gain and the 0.45% added methionine improved nitrogen retention and feed conversion when compared to the basal. When casein was used as the protein source, gains, feed conversion, digestibility of the various ration components, and nitrogen retention were significantly improved over the basal or methionine-supplemented soybean-protein diets. The differences in the digestibility of the ration components observed between soybean protein and casein at 3 weeks of age did not occur at 10 weeks of age. Retention of absorbed nitrogen followed the same pattern in both age groups. When fed to rats, casein and soybean oil meal produced comparable gains and feed conversions which were significantly greater than those produced by either Promine or Drackett C-1 assay protein. DL-methionine supplementation to the soybean-protein basal diet produced gains equal to those obtained with casein in contrast to the results obtained with pigs. L-lysine and/or DL-tryptophan added to this basal diet in the absence of added methionine had no significant effect on growth.