One-carbon metabolism (OCM) is an interconnected biochemical network that integrates methionine, choline, folate, vitamin B12 and related nutrients with transmethylation, remethylation, transsulfuration, phospholipid synthesis, nucleotide metabolism and cellular redox control. The system is especially relevant to dairy cattle during the transition from late gestation to early lactation, when dry matter intake often falls while requirements for glucose, amino acids, lipid transport, immune function and milk synthesis increase. Inadequate methyl-donor supply may constrain hepatic phosphatidylcholine synthesis and triglyceride export, while methionine availability also influences protein synthesis, antioxidant capacity and immune-cell function. The present review develops an Indian perspective by linking one-carbon nutrition with the diversity of cattle and buffalo production systems, fluctuating feed-resource availability, crop residues, oilseed cakes, agroindustrial by-products, seasonal heat stress and the metabolic risks observed around calving. Particular attention is given to the methionine and folate cycles, the choline-betaine pathway, transsulfuration, immunometabolism, liver lipid handling, reproduction and maternal-fetal programming. Recent mechanistic, metabolomic, molecular and metaanalytic evidence is integrated, including work published through 2026. Indian evidence from Kankrej cows, Surti buffaloes, Murrah buffaloes and Sahiwal transition cows is discussed alongside international dairy-cattle studies. The review argues that the next phase of research should move from single-nutrient supplementation toward systems-level assessment of bioavailable methyl-donor supply, rumen protection, metabolic phenotype, heat stress, breed or species effects and epigenetic outcomes. This framework could support more precise and context-specific methyl-donor nutrition for Indian dairy cattle and buffaloes.