EFFECTS OF HEAT-TREATMENT ON THE NUTRITIONAL-VALUE OF CONVENTIONAL AND LOW TRYPSIN-INHIBITOR SOYBEANS FOR CHICKS

Two experiments were conducted to assess the nutritional value of conventional and low trypsin inhibitor (TI) soybeans when fed in raw or heated form for chicks. In Experiment 1, four replicates of eight chicks per pen were fed com-based diets (19% CP, 3,158 kcal ME/kg) containing raw or heated conventional soybeans, raw or heated low TI soybeans, or conventional soybean meal (44% CP) plus oil. Heating was achieved by autoclaving the soybeans for 20 min at 1 1 0 C. Treatments were the same in Experiment 2 except that the soybeans were heated for 20 or 40 min. The TI activity of the low TI soybeans was approximately one-haff that of the raw conventional soybeans (9.6 versus 22.1 mg/g). Heating reduced the TI activity of both types of soybeans. Chick growth, feed utilization, and apparent retention of dietary DM and N were markedly depressed and pancreatic hypertrophy occurred when the raw conventional soybeans were fed. Depressions in performance and N retention and increases in pancreatic weights also occurred when chicks were fed raw low TI soybeans, but the responses were not as pronounced as when raw conventional soybeans were fed. Heat treatment reduced the TI activity of both types of soybeans and resulted in improved chick weight gain, feed:gain, and dietary DM and N retention, and reduced pancreatic weights (P < .01). In Experiment 1, chicks fed low TI soybeans heated for 20 min performed as well and had equivalent pancreas weights as those fed soybean meal. In Experiment 2, chicks fed either type of soybean heated for 40 min did not perform as well as those fed soybean meal. The results indicate that low TI soybeans are nutritionally superior to conventional soybeans, but some heating is required to maximize their nutritional value.