ARTICLE FEED & ADDITIVE MAGAZINE September 2025 57 Sick cows cost more, produce less, and are culled earlier. Whereas healthier cows stay in the herd longer, perform better, and require fewer interventions. Focusing on improved health means optimizing the entire system, from nutrient metabolism to feed efficiency, fertility and labor. IMMUNOMETABOLISM: NEW FRONTIER IN DAIRY NUTRITION Over the last two decades, we have learned that the immune system and metabolism are very interconnected, leading to the emergence of the field of immunometabolism (Basso et al., 2024). In dairy cattle, research in this area is helping us to understand how metabolism and immune function influence production, with a specific emphasis on how nutrition influences immunometabolism. One of the major regulators of immunometabolism via nutrition is mechanistic target of rapamycin (mTOR), which is sensitive to nutrients such as Met. A core aspect of immunometabolism is the investigation of how dietary and metabolic interventions can enhance immune health and responses to stressors. Researchers have explored how a variety of nutrients may influence and support immunometabolism, but of particular interest have been AA (Miyajima, 2020). Likely, the first thing that comes to mind when thinking about AA is their need for protein synthesis. However, there is growing knowledge that AA have functional roles beyond protein synthesis THE CLASSICAL FUNCTIONS OF METHIONINE AND mTOR Methionine an AA that has been recognized for its extensive functional roles: • One-carbon metabolism: Met is metabolized in these pathways, via which it provides methyl donors and enhances production of the antioxidants glutathione (GSH) and taurine (Coleman et al., 2020). • mTOR activation: Met is a known activator of mTOR, a nutrient-sensitive kinase (enzyme that transfers a phosphate group) that integrates signals from growth factors, energy and AA. In response to AA, mTOR itself is phosphorylated and subsequently activates pathways of protein and fatty acid synthesis (Laplante & Sabatini, 2009). This is a key mechanism behind increases in milk protein and fat when rumen-protected methionine (RPM) is added to dairy cow diets. These roles highlight how Met supports immunometabolism in dairy cows. NOVEL INSIGHTS INTO THE ROLE OF METHIONINE IN IMMUNE FUNCTION Beyond its effects on protein and fat synthesis, emerging research is indicating that mTOR is an important component of immunometabolism due to its key role in detecting and directing cellular processes. In immune cells specifically, mTOR regulates protein synthesis and cell proliferation, as well as integrates metabolic signals during immune cell activation (Weichhart et al., 2008). Moreover, mTOR target proteins have been reported to mediate inflammatory responses in immune cells, suggesting that Met can enhance immunometabolism not only through antioxidant pathways, but also via mTOR signaling (Figure 1). Example of mTOR Signaling in Immune Cells Using a Neutrophil Methionine mTOR Protein Synthesis Immune Responses and Activation Figure 1
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