The experiment was carried out on 151 Black-and-White cows from calving to 100 days of lactation. The animals were assigned to 8 groups by the analogue method. The influence of feeding diets containing different proteins from keratin meal (low rumen degradability) or lupin (high rumen degradability) and different energy sources such as slowly fermentable maize starch, easily fermentable barley meal or oil from rape seeds on the interaction of these factors in milk yield and composition, and feed conversion was studied. The cows were fed rations formulated according to INRA standards (IZ-INRA, 1997). The cows were milked twice daily and daily milk outputs were recorded. Milk samples were drawn once a week to determine fat, protein and lactose contents. Additional samples were taken at 35, 84 and 100 days of lactation to determine the urea content; fatty acids were determined in samples taken on day 100 of lactation. The body weight of cows was determined on day 21 prior to calving and at 2, 10, 35, 84 and 100 days after calving. The results of the experiment showed that despite the rations being balanced for energy and protein, the type of dietary protein (different rumen degradability coefficients) can affect the yield of milk and its components in high-yielding cows. The extent of starch degradation in the rumen appeared to be of limited influence on these parameters. The highest milk protein content was obtained with the lupin-barley combination (a significant protein by starch interaction) indicating that adequate synchronization of energy and protein for bacterial yield in the rumen may affect the level of protein in milk. Increased intake of rape seeds oil had a favourable effect on milk and lactose yield without a significant effect on milk composition. The effect of rape seeds on milk performance was not related to the other feed components in terms of the rate of protein and carbohydrate degradation, as the protein x starch x oil interaction was not significant. The source of protein, starch and oil from rape seeds had only a slight effect on changes in the fatty acid composition of milk fat.