Soybean meal (SBM) is often included in cereal-based diets for growing pigs because it provides a well-balanced profile of digestible amino acids (AA), which maximizes growth performance and protein synthesis. However, in recent years, SBM has often been partially replaced by crystalline AA or alternative protein sources such as corn distillers dried grains with solubles (DDGS) or corn protein. These co-products are by-products of the ethanol and vegetable oil industries and are commonly used in swine diets due to their availability and lower cost. Although they provide some indispensable AA, they have a less balanced AA profile and greater fiber concentrations than SBM, which may result in reduced AA digestibility, nitrogen retention, and energy utilization in pigs. However, pigs have become leaner and have greater requirements for dietary AA to support protein synthesis. In addition, it is often assumed that replacing SBM with corn and crystalline AA increases the energy of the diet, but recent data indicate that SBM may provide as much or more digestible energy (DE) and metabolizable energy (ME) than previously estimated. Therefore, it is possible that replacing SBM with corn co-products and crystalline AA may result in a reduction of nitrogen and energy utilization and increase nitrogen excretion in manure. Therefore, the objective of this work was to test the hypothesis that feeding intact protein from SBM to growing pigs, instead of combinations of SBM with crystalline AA or co-products such as DDGS or corn protein, results in greater nitrogen retention and greater DE in the diet without affecting ME.

Lee, Su A, Chad B. Paulk, Hans H. Stein. 2025.

Pistachio blanks are coproducts of pistachio processing and are discarded due to their hollow shells or immature nuts, which make them unusable as human food. Pistachio blanks float in water and the annual production is estimated to be between 50,000 and 70,000 metric tons. A similar coproduct, pistachio shell powder, was recently demonstrated to provide significant amounts of energy in diets for sows. However, there is no information about the digestibility of amino acids (AA) in pistachio blanks when fed to pigs. Although AA concentration in pistachio blanks is low, there is a need for determining standardized ileal digestibility (SID) of AA in pistachio blanks. Therefore, an experiment was conducted to test the hypothesis that the SID of AA in pistachio blanks are comparable to those in soybean meal (SBM) when fed to growing pigs.

Ruiz-Arias, N. C.,  S. A. Lee, H. H. Stein. 2025. There are only minor differences among soybeans grown in different areas of the United States in nutrient composition and digestibility of amino acids by growing pigs. Animal Feed Science and Technology 323 (2025) 116297. doi.org/10.1016/j.anifeedsci.2025.116297. Link to full text.

Ibagon, Jimena A., Su A. Lee, Diego A. Rodriguez, C. Martin Nyachoti, Hans H. Stein. 2024. Reduction of particle size of field peas (Pisum sativum L.) increases net energy and digestibility of starch when fed to growing pigs, but there is no difference in  nutritional value between peas from the United States and peas from Canada. J. Anim. Sci.

Stein, Hans H. 2024. The pig is an excellent model to determine amino acid digestibility of human foods and to generate data needed to meet human amino acid requirements. Front. Nutr. 11:1434430. DOI 10.3389/fnut.2024.1434430 Link to full text.

Ruiz-Arias, Nelson C., Su A Lee, Hans H. Stein. 2024. Standardized ileal digestibility of amino acids and concentration of metabolizable energy in three sources of corn protein fed to weanling pigs. J. Anim. Sci Vol. 102, Suppl. S2. P 94 - 95. doi.org/10.1093/jas/skae102.106 Link to abstract.

Cristobal, Minoy, Su A Lee, Andrea P. Mallea, Leidy J. Torres-Mendoza, Jessica P. Acosta, Carl M. M. Parsons, Hans H. Stein. 2024. Effect of feeding intact protein from soybean meal instead of crystalline amino acids on growth performance, protein synthesis, and immune response of growing pigs. J. Anim. Sci Vol. 102, Suppl. S2. P 45 - 46. doi.org/10.1093/jas/skae102.054 Link to abstract.

Apparent ileal digestibility (AID) of amino acids (AA) is affected by dietary AA levels because of different contributions of endogenous AA to the ileal digesta from pigs fed diets with different levels of AA. Because of the influence of dietary protein and AA on calculated values for AID, values for AID obtained in individual feed ingredients are not always additive in mixed diets. Therefore, values for standardized ileal digestibility (SID) of AA, which are corrected for the basal ileal endogenous losses of AA, are used in diet formulations to avoid the influence of endogenous AA on digestibility values, and SID values are, therefore, additive in mixed diets.

When the direct procedure is used to determine AA digestibility, diets containing cereal grains are sometimes formulated to contain AA below the requirement. In contrast, if the SID of oilseed meals or other protein-rich ingredients are determined, concentrations of AA may be at or above the requirement. Because the influence of the basal endogenous losses of AA is eliminated in the calculations of SID values, it is assumed that values for SID are not influenced by dietary concentrations of AA. However, to our knowledge this hypothesis has not been experimentally verified, but it is an important question because it may influence how diets used in digestibility experiments are formulated. Therefore, four experiments were conducted to test the hypothesis that the SID of AA by growing pigs is not influenced by dietary AA levels.