Determination and prediction of net energy of soybean meal fed to pregnant sows by indirect calorimetry

Objective: The study was conducted to investigate the appropriate substitution level of soybean meal (SBM) for determining its net energy (NE), and establish NE prediction equation of SBM based on the determined NE values for pregnant sows. Methods: In Exp. 1, eighteen pregnant sows (Landrace×Yorkshire; parity, 2 to 3) with an initial body weight (BW) of 221.2±2.6 kg at mid-gestation were blocked by BW and randomly assigned into 3 groups. Three groups fed with a corn-SBM basal diet and two test diets with 15% and 30% energy-supplying components replaced by SBM, respectively. In Exp. 2, six diets were formulated including a corn-SBM basal diet and five SBM diets (based on the substitution level determined of Exp. 1) with different soybean sources and processing methods. Moreover, 12 pregnant pigs (BW = 209.0±3.0 kg; parity, 3 to 4) at mid-gestation were arranged in a 6×3 Youden square design. Results: Increasing substitution levels of SBM linearly increased (p<0.05) fecal and urinary nitrogen excretion and the ratio of urinary energy to digestible energy (DE), while linearly decreased (p<0.05) the ratio of metabolizable energy (ME) to DE and tended to linearly decrease dietary ME (p = 0.066) and NE (p = 0.074). The coefficient of variation for the NE of SBM was lower at a 15% substitution level compared to a 30% substitution level. The nutritional compositions of SBM are influenced by the soybean sources and processing methods. As dry matter basis, NE values of SBM ranged from 11.1 to 12.7 MJ/kg and the best-fitted prediction equation for NE of SBM was: NE (MJ/kg) = −91.71+5.35×gross energy (%)−0.03×neutral detergent fiber (%; R² = 0.96). Conclusion: A substitution level of 15% was more appropriate to determine NE of SBM. Furthermore, NE values of SBM can be predicted based on their chemical compositions.