Symposium review: One-carbon metabolism and methyl donor nutrition in the dairy cow

摘要

The present review focuses on methyl donor metabolismand nutrition in the periparturient and lactatingdairy cow. Methyl donors are involved in one-carbonmetabolism, which includes the folate and Met cycles.These cycles work in unison to support lipid, nucleotide,and protein synthesis, as well as methylationreactions and the maintenance of redox status. A keyfeature of one-carbon metabolism is the multi-step conversionof tetrahydrofolate to 5-methyltetrahyrofolate.Homocysteine and 5-methyltetrahyrofolate are utilizedby vitamin B_(12)-dependent Met synthase to couple thefolate and Met cycles and generate Met. Methioninemay also be remethylated from choline-derived betaineunder the action of betaine hydroxymethyltransferase.Regardless, Met is converted within the Met cycle toS-adenosylmethionine, which is universally utilized inmethyl-group transfer reactions including the synthesisof phosphatidylcholine. Homocysteine may also enterthe transsulfuration pathway to generate glutathioneor taurine for scavenging of reactive oxygen metabolites.In the transition cow, a high demand exists forcompounds with a labile methyl group. Limited methylgroup supply may contribute to inadequate hepaticphosphatidylcholine synthesis and hepatic triglycerideexport, systemic oxidative stress, and compromisedmilk production. To minimize the perils associated withmethyl donor deficiency, the peripartum cow relies onde novo methylneogenesis from tetrahydrofolate. Inaddition, dietary supplementation of rumen-protectedfolic acid, vitamin B_(12), Met, choline, and betaine arepotential nutritional approaches to target one-carbonpools and improve methyl donor balance in transitioncows. Such strategies have merit considering researchdemonstrating their ability to improve milk productionefficiency, milk protein synthesis, hepatic health, andimmune response. This review aims to summarize thecurrent understanding of folic acid, vitamin B_(12), Met,choline, and betaine utilization in the dairy cow. Methyldonor co-supplementation, fatty acid feeding strategiesthat may optimize methyl donor supplementation efficacy,and potential epigenetic mechanisms are alsoconsidered.