In the period from 2004 to 2011, seven trials on lactating cows were conducted to evaluate the relationship between the amounts of energy required, and milk production and composition. In total, 392 observations on 132 animals were selected due to different levels of energy intake. The observations were classified into three groups according to the amount of total digestible nutrients (TDN) provided by the diets, i.e. 67, 75 and 94% TDN. Such characteristics as proportion of energy provided in relation to cow requirements, experiment duration, daily milk production, and fat, protein and lactose contents, total solids percentage, somatic cell score, titratable acidity and ethanol stability test were considered. Levels of supplied energy were positively related with milk production, ethanol stability and lactose content. Seven variables were regarded as discriminant between levels of supplied energy, including proportion of provided energy related to cow requirement, duration of the experiments, ethanol stability test and milk production, and explained more than 70% of the variance among the observations. Milk production increased linearly with the proportion of the supplied energy from 14, 16 to 19 kg · d⁻¹ per cow, while lactose content increased from 4.37 to 4.56% as the level of TDN attained 93% of estimated requirements. Milk stability increased from 74.2 to 76.4% as the level of TDN attained 79% of estimated requirements. Increased level of the supplied energy related to requirements of lactating cows improved milk yield, milk stability and lactose content.