Poultry are primarily fed corn- and soybean-based diets in the United States. Soybean meal (SBM) has a high crude protein content and an excellent amino acid profile; however, it contains several antinutritional factors that have been shown to hinder bird performance. Soybean crush plants utilize a toasting step to degrade these heat-labile antinutrients in meal, but many factors vary across crush plants that can make it difficult to determine processing adequacy. Furthermore, current analytics may not properly indicate optimal processing. Therefore, two experiments were conducted. The objectives of the first experiment were to characterize under-processed, peak-processed i.e. optimally processed, and over-processed solvent-extracted SBM from a commercial crush plant with trypsin inhibitor activity (TIA) using the new USDA-ARS method, TIA with the AOCS method, urease, solubility in potassium hydroxide (KOH) and protein dispersibility index (PDI) in addition to evaluating assay variation within and across commercial laboratories. The objective of the second experiment was to determine the effect of the three aforementioned SBM types on broiler performance when included in mash diets and fed for 21 days. Three diets were formulated to 85% crude protein and digestible amino acid requirements, differing only in the type of SBM. A nutritionally adequate positive control (PC) diet was also formulated. Diets were fed in mash form. Analysis of the SBM samples indicated an increase in trypsin inhibitor (TI) from under to peak-processed, then a decrease from peak to over-processed. Urease, KOH, and PDI analysis revealed variation within and among laboratories, with the most consistent measure of processing adequacy being urease. Urease decreased with increasing processing according to 2 of the 3 laboratories. Live weight gain (LWG) increased by 52 g for birds fed the peak-processed diet relative to the under-processed diet (P < 0.05). Feed conversion ratio increased when birds were fed the under-processed diet relative to all other diets (P < 0.05). Broiler chick live performance demonstrated nutritional differences in soybean meal samples that were not consistently identified through various ingredient assays. Bird performance results aligned best with the Urease assay.

An appreciation that commercially produced under processed soybean meal decreased chick performance and was most aligned with the urease assay. Improved processing that decreases urease activity should be a target of crush plants that will improve product quality and market opportunities.