Comparison of the Nutritive Value of Different Heat-Treated Commercial Soybean Meals: Utilization by Chicks in Practical Type Rations

Abstract

Four commercially heat-treated soybean meals (Subnormal, Normal, Over, or Rumen Escape) were evaluated on the basis of their nutritive quality using proximate analysis, amino acid composition, in vitro tests (trypsin inhibitor activity, urease activity, protein dispersibility index, nitrogen solubility index), Hunterlab color values, and a chick bioassay. Each soybean meal (SBM) was incorporated into a practical-type broiler diet, formulated to contain 100% (Experiment 1) or 85% (Experiment 2) of the protein requirement.Compared to the Normal meal, excessively heat-treated SBM (Over or Rumen Escape) had lower crude protein (essential and nonessential amino acids); less trypsin inhibitor and urease activities; reduced protein dispersibility and nitrogen solubility indices; and was darker in color (redness). The nutritive profile of the Subnormal SBM was nearly identical to that of the Normal meal except that trypsin inhibitor activity, urease activity, nitrogen solubility index, and color scores (lightness and yellowness values) were reduced in the Normal meal due to processing. The protein dispersibility index was highest in the Normal meal, followed by the Subnormal, Over, and Rumen Escape.Performance data (body weight gain, feed conversion, relative pancreas weight) among broiler chicks fed either Subnormal, Over, or Rumen Escape SBM did not differ significantly compared to birds fed Normal SBM in Experiment 1 or Experiment 2. Moreover, supplementing diets containing Over or Rumen Escape heat-treated SBM with lysine (Experiment 2) did not significantly improve performance.These results indicate that the nutritive quality of commercially processed SBM should be assessed not only on the basis of in vitro tests but also on the basis of a chick bioassay.