FROM THE FARM REPORT: RUMEN-PROTECTED METHIONINE:WHEN SHOULD I FEED IT TO MY COWS?

Methionine is more than just another nutrient in a dairy cow’s ration. As one of the key building blocks of protein, it influences not only how much milk a cow produces but also how efficiently she uses the nutrients in her diet. Over the years, advances in feed technology have made it possible to deliver methionine in a form that bypasses the rumen and reaches the small intestine, where it can be fully absorbed. This rumen-protected form of methionine has transformed the way nutritionists balance rations, shifting the focus from simply meeting crude protein needs to precisely supplying the right amino acids. Today, methionine is recognized as a cornerstone of modern dairy nutrition, with benefits that extend beyond milk yield to cow health, resilience during the transition period, and overall efficiency of production.

Milk Production Benefits

A meta-analysis of 21 studies showed that feeding RPM around calving increases dry matter intake, milk yield, and component yields (Zanton and Toledo, 2024). The predicted gain at 21 days in milk (DIM) was substantial: +118 g/day of milk fat and +92 g/day of milk true protein. Milk yield increases varied by study, but the consistent pattern was higher output when methionine was included from the transition period onward.

In individual trials, responses differed by parity. In multiparous cows, methionine supplementation improved fat-corrected milk persistently through the first five weeks postpartum (Potts et al., 2020). Primiparous cows showed modest gains, reflecting their lower production potential, but the trend toward improved efficiency was consistent.

Milk Protein Response

Methionine is the first limiting amino acid for milk protein synthesis. Numerous studies have confirmed that supplementing RPM increases milk protein concentration and yield, particularly during early lactation (Osorio et al., 2013; Potts et al., 2020). The magnitude of the response, however, is variable. In some trials, increases were modest, with gains of 30 to 50 g/day of milk protein. In others, responses were much larger, exceeding 100 g/day of additional protein yield. The recent meta-analysis estimated an average benefit of about +92 g/day of milk true protein at 21 days in milk, although some studies reported little to no effect when baseline diets already provided ample methionine. This variability reflects differences in parity, stage of lactation, diet formulation, and production level. Still, the overall trend is clear: methionine supplementation consistently supports casein synthesis in the mammary gland. Importantly, the response is strongest in early lactation and gradually diminishes as cows progress through lactation, reinforcing the need for timely supplementation.

Health and Immunometabolic Status

Beyond milk, methionine plays vital roles in immunity and liver function. Supplementation during the transition period has been shown to:

Improve liver antioxidant status, with higher glutathione reserves (Zhou et al., 2016).

Enhance immune cell function, including neutrophil phagocytosis and oxidative burst activity (Zhou et al., 2016).

Lower markers of inflammation, such as haptoglobin, while increasing albumin and paraoxonase (Zhou et al., 2016).

These findings suggest that methionine helps cows cope with oxidative stress and immune suppression typical of early lactation. Healthier cows are more resilient, with reduced risk of transition disorders.

Methionine and Choline: Partners in One-Carbon Metabolism

Methionine and choline are metabolically intertwined through one-carbon metabolism. Both serve as methyl donors, essential for synthesis of phosphatidylcholine, a molecule critical for exporting fat from the liver. Studies demonstrate that when both nutrients are fed together, the effects are not always additive. In some trials, choline raised milk yield only when methionine was not supplemented, highlighting interdependence (Potts et al., 2020). Other studies revealed that methionine and choline together influenced hepatic gene expression related to lipid metabolism and methyl group transfer (Potts et al., 2023). This means that nutritionists should consider balancing methyl donor supply, ensuring that neither methionine nor choline is limiting. In some herds, methionine may be the priority; in others, choline may unlock additional benefits.

Until When Do Cows Respond?

A key question for nutritionists is: how long should we continue feeding RPM? The meta-analysis provides a suggestion. While responses in milk fat and protein yield were robust at 21 DIM, the magnitude of benefit declined steadily as lactation progressed (Zanton and Toledo, 2024). By mid-lactation, production responses were smaller and less consistent.

This pattern reflects biology. Early lactation is marked by negative energy and protein balance, with high demand for methyl donors to support milk synthesis, liver function, and immune resilience. As cows move beyond 60–90 DIM, nutrient partitioning stabilizes, and methionine is less limiting.

Practical takeaway:

RPM should be viewed as a transition and early lactation tool, with the greatest return on investment when fed from three weeks prepartum through at least 60 DIM. Later in lactation, supplementation may still support milk protein yield and protein, but the responses are modest compared with the critical transition window. In other words, if you want to capture the full benefits of methionine—higher milk and protein yield, improved immunity, and healthier cows—the time to invest is before and just after calving.

— Marcos Marcondes

mmarcondes@whminer.com