Nutritional evaluation of soybeans varying in trypsin inhibitor content

A series of experiments was conducted to assess, by various methods, the nutritional value of a raw, Kunitz inhibitor-free, low trypsin-inhibitor soybean variant (LTS) in comparison with raw conventional soybeans (RCS) and heated dehulled soybean meal (HDS). The gross energy, protein, and amino acid concentrations of LTS were similar to those of RCS. The protein quality of the soybeans was compared in two trials in which young chicks were fed 9% or 16% CP diets containing one of the soybeans as the sole source of dietary protein. The protein quality of LTS was superior to that of RCS but inferior to that of HDS. True digestibilities of amino acids and TMEn were determined with a precision-fed cockerel assay using conventional and cecectomized birds. No significant effect of bird type on digestibility was found. The mean digestibility of 16 amino acids in RCS, LTS, and HDS was found to be approximately 68, 83, and 92%, respectively. The TMEn of LTS was greater than that of RCS. Chick growth assays indicated that amino acid bioavailability values of lysine and TSAA for LTS were greater than those for RCS but slightly lower than those for HDS. In an additional chick assay with a corn and HDS diet (22% CP), the dietary HDS protein was replaced with LTS or RCS protein at 25, 50, 75, or 100%. Performance of chicks fed LTS was better than that of chicks fed RCS at all replacement levels, but the difference was not significant at the 25% replacement level. Feed efficiencies of chicks fed 25 or 50% of the dietary soybean protein as LTS were not significantly different from that of chicks fed the corn and HDS control diet. The results of the present study indicated that the nutritive value of LTS is substantially greater than that of RCS but somewhat lower than that of HDS.