Comparison of laboratory analytical values and in vivo soybean meal quality on pigs by employing soyflakes heat-treated under different conditions

White soyflakes (SFs) were heat-treated by steam pressure cooking for four conditions to compared laboratory analytical values with in vivo qualities of soybean meal. The heat-treatment conditions consisted of no heat-treatment (SF-1), 5 min at 95 °C (SF-2), 5 min at 110 °C (SF-3), 15 min at 110 °C (SF-4), and 60 min at 110 °C (SF-5) under 1.07 kg/cm2 pressure. The pepsin digestibility (PD), urease activity index (UAI), protein solubility in 0.2% KOH solution (KOH), and protein dispersibility index (PDI) were measured. Twenty pigs (14.1 ± 0.92 kg) were used to determine the energy and nitrogen digestibility. Experimental diets were formulated to contain 217 g/kg CP and 14.1 ME MJ/kg. Two growth trials were also conducted with 60 pigs per trial. The diets contained 191 g/kg CP and 14.2 ME MJ/kg. The nitrogen and energy digestibility were highest in SF-4 (P<0.05), and increased with increasing heat treatments (P<0.05), and also the BW, ADG, ADFI and FE were significantly increased with increasing heat treatment (SF-1, SF-2, SF-3, and SF-4) (P<0.05). The extremely heat-treated SF (SF-5) showed diminished digestibility in both nitrogen and energy and growth performance (P<0.05). The PD was not useful to predict in vivo quality due to their small decrease (95–93%) during heat treatment. The abrupt drop of UAI was sensitive to detect under heat treatment (SF-1 and SF-2); however, the constant value (nearly zero) in adequate and over heat treatments (SF-3, SF-4, and SF-5) revealed their useless in adequate and over heat treatments (r = −0.40). The KOH was sensitively changed from 96 to 84% after low heat treatment (SF-0 and SF-1), and also decreased from 76 to 41% after extreme heat treatment (SF-4 and SF-5). They exhibited linear negative correlation through heat treatments (r = −0.97). The PDI dropped steeply (65–22%) after low heat treatment (SF1 to SF-3), and gradually decreased with further heat treatments (r = −0.68). The analytical value of PDI to under heat treatment was much more correlation with in vivo quality than did UAI. These results suggested that the combination of the KOH and PDI is more effective at predicting the in vivo quality from the laboratory analytical value than the combination of the UAI and KOH.