The following supplements were used in the feeding of high yielding dairy cows starting 3 weeks before calving to day 100 of lactation: a fat supplement in the form of calcium-magnesium soaps, Erafet, (group I), Erafet plus rapeseed meal (group II), rapeseed cake containing 19.5% crude fat (group III). During the first three months of lactation, a increase in the daily FCM yield was noted in the experimental groups as compared with the control group with no supplements, i.e. by 4.6, 11.6 and 8.5%, respectively in groups I - III. After withdrawing supplementation, during the subsequent four months of lactation, the cows in the experimental groups produced 1.7, 3.3 and 4.1% more milk, respectively, than the controls. The milk fat from experimental cows contained significantly more oleic (by 7.5 to 10.0%) and stearic acids (from 5.9 to 25.1%) and less C4-C16 acids.