Concentrations of digestible and metabolizable energy and amino acid digestibility by growing pigs may be reduced by autoclaving soybean meal

Two experiments were conducted to test the hypothesis that both the degree of heating and the time heat is applied will affect standardized ileal digestibility (SID) of amino acids (AA), and concentrations of digestible energy (DE) and metabolizable energy (ME) in soybean meal (SBM) fed to growing pigs. One source of SBM was divided into 9 batches and used in 2 experiments. One batch was not autoclaved and considered the control. Two batches were autoclaved at 110 °C for 15 or 30 min and 6 batches were autoclaved at 150 °C for 3, 6, 9, 12, 15, or 18 min. In Exp. 1, a corn-based diet and 9 diets based on corn and each source of SBM were fed to 20 barrows (43.6 kg) that were used in a replicated 10 × 4 Youden square design. Urine and fecal samples were collected for 5 days after 7 days of adaptation. In Exp. 2, nine cornstarch-based diets included 400 g/kg of each of the 9 sources of SBM. An N-free diet was also used. Ten growing barrows (36.8 kg) with a T-cannula installed in the distal ileum were allotted to a 10 × 7 Youden square design with 10 diets and 7 periods. Ileal digesta were collected on d 6 and 7 of each 7-d period. Results from the experiments indicated that the ATTD of GE, and the DE and ME, the SID of crude protein (CP) and all AA were less (P < 0.001) if SBM was autoclaved at 150 ºC than at 110 ºC. The ATTD of GE, the DE and ME, and the SID of CP and AA were not affected by increasing duration of autoclaving at 110 °C, but there were linear reductions (P < 0.001) in ATTD of GE, in DE and ME, and in SID of all AA if duration of autoclaving was increased at 150 ºC. These observations demonstrate that over-heating of SBM not only results in reduced SID of AA, but ATTD of GE will also be impaired with a subsequent reduction in concentrations of DE and ME.