Work in recent years has highlighted performance improvements with increasing soybean meal, even when formulated net energy is held constant. To explain these results, factors such as limitations in methodologies for net energy estimation, modern genetics of animals and seed varieties, conditionally essential amino acids, and extra-nutrient effects of SBM functional compounds have been discussed. To further explore the functional effects of SBM in swine, this work set out to survey biomarker responses and performance outcomes in a commercial production setting in response to increasing SBM inclusion.

Increasing SBM levels elevated circulating serum IL-8, which acts as a chemokine and a primer for immune responses, independent of DDGS inclusion. Regardless of DDGS inclusion, increasing SBM elevated serum IL-10, an immune regulator, preventing excessive immune activation and excessive inflammation. Further, SBM tended to decrease circulating granulocyte macrophage-colony stimulating factor, an immune stimulator, indicating a decrease in immune cell proliferation in pigs fed diets containing higher SBM levels.

Because immune activation and oxidative stress increase maintenance energy requirements and divert energy away from productive processes, the coordinated modulation of cytokines and acute phase proteins observed with increasing SBM may contribute to differences in performance outcomes under commercial conditions. These results support the concept that SBM provides functional effects beyond its nutritional value, influencing physiological processes that are relevant to production outcomes, but further research is warranted to truly understand if they have a direct impact on maintenance energy cost.

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