Soybean meal (SBM) is the primary source of amino acids (AA) and energy in diets for swine throughout the world. However, less SBM is often used in diets to decrease nitrogen excretion and environmental pollution. Nonetheless, it is demonstrated that lowering dietary protein does not consistently deliver the same performance of pigs as of pigs fed high protein diets, even though all indispensable AA meet the requirements of pigs. It is possible that soybean-derived bioactive compounds (i.e., soy isoflavones and saponins) in SBM act as immunomodulators, which improve the performance of pigs. It is also possible that low-protein diets contain nitrogen below the requirements for pigs to maximize growth. However, no data are available to prove this hypothesis. Therefore, the objective of this experiment was to test the hypothesis that reducing the dietary protein by decreasing the SBM and increasing crystalline AA in diets may have influence growth performance, carcass composition, and meat quality and that soy isoflavones act as immunomodulators, which may improve the immune system and thus results in better performance of pigs fed low-protein diets.

Bailey, Hannah M., Natalia S. Fanelli, Joy M. Campbell and Hans H. Stein. 2025. Effects of spray dried plasma on litter growth performance and oxidative stress and inflammation of sows kept in a hot environment. Journal of Animal Science and Biotechnology (2025) 16:13. doi.org/10.1186/s40104-024-01139-9 Link to full text.

Ibagon, Jimena A., Charmaine D. Espinosa, Hans H. Stein. 2025.

The use of synthetic amino acids (AA) in diets for pigs has increased in the past few decades due to increased availability and reduced prices of these AA. The increased use of synthetic AA has caused a reduced need for inclusion of soybean meal (SBM) in diets. For instance, a common grower pig diet without synthetic AA needs around 35% SBM to full fill the requirements for all indispensable AA, but a diet with 5 synthetic AA only requires 17% SBM. It has generally been assumed that pigs fed diets containing synthetic AA will have growth performance, protein deposition, and carcass quality that is no different from that of pigs fed diets based in which the majority of the AA are furnished by SBM as long as the requirements for all digestible AA are met. It has also been assumed that diets formulated with large amounts of synthetic AA, compared with diets based on SBM provide more net energy to pigs because these diets contain more corn and less SBM. However, some of these assumptions are not based on strong scientific evidence, and results of recent research has raised doubts about previously assumed effects of using synthetic AA. Therefore, the objective of this experiment was to test the hypothesis that the use of synthetic AA instead of some of the intact protein from SBM does not impact growth performance, carcass composition, energy deposition, blood cytokines or abundance of intestinal amino acid transporters when fed to growing pigs.

Diets with high inclusion of corn fermented protein (CFP) may have an excess of Leu, which has a negative impact on the growth performance of pigs. Tryptophan is a precursor of serotonin, which is a neurotransmitter that is critical for feed intake regulation, and excess dietary Leu may reduce synthesis of serotonin in the brain by preventing Trp from being transported to the brain. Reduced serotonin synthesis can result in reduced feed intake and pigs with reduced feed intake due to excess Leu also have reduced growth performance. As a consequence, if diets are formulated based on CFP instead of soybean meal (SBM), diets need to be fortified with extra Trp to account for the reduced efficiency of Trp due to the excess Leu in corn protein. However, a quantitative assessment of how much extra Trp is needed in diets based on CFP instead of SBM has not been conducted. Therefore, an experiment was conducted to test the hypothesis that the optimum Trp:Lys ratio in diets for growing pigs is greater if CFP rather than SBM is used as the protein source in the diets. 

Soybean meal (SBM) is the primary source of amino acids (AA) and energy in diets for swine throughout the world. However, less SBM is often used in diets to decrease nitrogen (N) excretion and environmental pollution. Nonetheless, it is demonstrated that lowering dietary protein does not consistently deliver the same performance of pigs as of pigs fed high protein diets, even though all indispensable AA meet the requirements of pigs. It is possible that soybean-derived bioactive compounds (i.e., soy isoflavones and saponins) in SBM act as immunomodulators, which improve the performance of pigs. It is also possible that low-protein diets contain N below the requirements for pigs to maximize growth. However, no data are available to prove this hypothesis. Therefore, the objective of this experiment was to test the hypothesis that N balance of pigs is not affected by reducing dietary protein if soy isoflavones or N source are supplemented in diets.

Ruiz-Arias, N. C., S. A Lee, and H. H. Stein. 2024. Full-fat soybeans: Valuable source of energy, digestible P for pigs. National Hog Farmer. On-line edition. Oct. 31, 2024. Link to full text.

Kim, Yeonwoo, Su A. Lee, and Hans H. Stein. 2024. Determination of energy values in pistachio shell powder and soybean hulls fed to gestating and lactating sows. Translational Animal Science, 2024, 8, txae135. doi.org/10.1093/tas/txae135 Link to full text.

Velayudhan, Deepak E., Manik M. Hossain, Jinyoung Lee, Hans H. Stein, Charles Martin Nyachoti. 2024. Standardized total tract digestibility of phosphorus in canola meal fed to gestating or lactating sows without or with a multi-enzyme complex. Animal Feed Science and Technology 316 (2024) 116068. doi.org/10.1016/j.anifeedsci.2024.116068.