Rumen protected methionine and the genome: nutrigenomics and beyond

Abstract Text: The importance of methionine (Met) as one of the most-limiting amino acids for milk protein synthesis in dairy cows is well-established. Positive effects of supplementation of Met also have been observed in terms of milk production and milk fat yield. Recent work has revealed that the benefits of rumen-protected methionine (RPM) during the transition period are not only a function of greater voluntary dry matter intake postpartum but also a better immune-metabolic status, i.e. lower concentrations of inflammation markers and better antioxidant capacity. Several of these molecules circulating in the blood are synthesized in liver, which readily utilizes exogenous Met in the 1-carbon metabolism cycle leading to the synthesis of key intermediates such as S-adenosylmethionine (SAM), phosphatidylcholine (PC), and glutathione. These intermediates play crucial roles in liver lipid metabolism, e.g. PC is essential for synthesis of very-low density lipoproteins (VLDL) which help export triacylglycerol from liver, thus, reducing the likelihood of the cow developing fatty liver and ketosis. The molecule SAM is extremely important as a methyl donor, not only for intermediary metabolites but also for the process of DNA methylation which is a fundamental process occurring in mammalian cells. Methylation of DNA alters gene expression in cells, and is one of the main causes of epigenetic modifications. Therefore, besides its well-established role in milk protein synthesis and liver lipid metabolism, the impact of an optimal level of RPM fed to dairy cattle could have implications at the gene level; not only on the cow but also on the developing calf. The advent and application of genome-enabled technologies such as “transcriptomics" and “metabolomics” along with “bioinformatics” analyses are widely-recognized as tools that have helped advance the knowledge of animal function. Application of these tools is ideal for the study the effects of RPM on tissue/cell metabolism/function during key life stages of dairy cattle such as the transition period. The aims of this presentation is to provide an overview of the effects of RPM in dairy cattle at the molecular level including epigenetics, nutrigenomics, and metabolomics. Emphasis will be placed on physiological interpretation of these types of data in the context of RPM nutrition. Examples of nutrigenomics and metabolomics work conducted with RPM in terms of liver metabolism and function will be highlighted. Use of these data for identification of biomarkers with potential for use as predictors for animal at greater risk of developing metabolic disorders postpartum will be discussed. 

Keywords: transition period, nutrition, genomics