The objective of this project was to study balanced amino acids (AA) and fatty acids (FA) feeding strategies for early lactation cows. The first experiment was to study lactation performance affected by feeding reduced crude protein (CP) diets, with adequate metabolizable protein (MP) and supplemental lysine and methionine from calving to 15 wk postpartum. Results indicated that cows the diets could maintain milk performance compared with cows fed high CP diet, but diets with deficient Lys depressed milk fat synthesis. The second experiment was to study the effects of balanced AA feeding strategies on profitability and environmental impacts on commercial farms. Results indicated that primi- and multi-parous cows fed low CP diets with adequate MP, and supplemental lysine and methionine could maintain milk performance, increase profitability and decrease N excretion in urine, feces, and ammonia emission on a commercial farm. The third experiment was to study effects of long chain FA on adipogenesis of bovine stromal vascular cells (SVC). Results indicated that adipogenesis of SVC was differentially affected by dose and type of FA. Also oleic and linoleic acids had more positive effects on adipogenesis in commitment and maturation stages than myristic, palmitic and stearic acids. The fourth experiment was to study effects of oleic and stearic acids on lactation performance of cows from 2 to 13 wk postpartum. Results indicated that cows fed oleic acid had less dry matter intake, but similar yields of milk and milk components since cows fed oleic acid partitioned more dietary nutrients to mammary gland rather than body fat than cows fed stearic acid. The fifth experiment was to study milk 13C and 15N fractionations in estimating energy balance and nutrient contributions of body tissues to milk synthesis. Results indicated that C mobilized from body fat and N mobilized from muscle were the major reasons in shifting milk 13C and 15N fractionations postpartum, and further demonstrated that tissue mobilization was one of major drivers for milk synthesis in early lactation. Overall, the research project well illustrated lactation performance affected by AA and FA in multiple scenarios.