APPARENT DIGESTIBILITY OF AMINO-ACIDS IN RAW AND HEATED CONVENTIONAL AND LOW-TRYPSIN-INHIBITOR SOYBEANS FOR PIGS

An experiment was conducted with ileally cannulated pigs to determine the apparent digestibility of amino acids and N in raw or heated conventional or low-trypsin-inhibitor soybeans. Six littermate barrows initially averaging 24 kg were fed cornstarch-based diets (10.5% CP, .68% lysine, 3,558 kcal of ME/kg) supplemented with raw (unheated), conventional soybeans; raw, low-trypsin-inhibitor soybeans; heated, conventional soybeans; heated, low-trypsin-inhibitor soybeans; or solvent-extracted soybean meal. Heating was achieved by autoclaving soybeans (after grinding) for 20 min at 110-degrees-C. The urease activities of the two raw soybean sources were similar, but the trypsin inhibitor activity of the raw, low-trypsin-inhibitor soybeans was about one-half that of the raw, conventional soybeans. The lower trypsin inhibitor activity of the raw, low-trypsin-inhibitor soybeans was associated with an improvement in the apparent digestibility of amino acids and N compared with the raw, conventional soybeans (P < .05). Heating reduced the urease and trypsin inhibitor activities and improved (P < .05) the apparent digestibility of amino acids and N in both types of soybeans. However, the heated, conventional soybeans contained more trypsin inhibitor activity than the heated, low-trypsin-inhibitor soybeans and the digestibilities of the amino acids were lower (P < .05). Although the urease and trypsin inhibitor activities of the two heated soybean sources were similar to or less than those of soybean meal, the digestibilities of amino acids were not as great (P < .05) in the heated soybeans as in soybean meal. The results indicate that low-trypsin-inhibitor soybeans are a superior protein source to conventional soybeans, but adequate heating is required to maximize their nutritional value.