Multiparous sows (n 17) were included in a controlled cross-over-study in order to investigate the influence of a natural source of conjugated linoleic acid (CLA) (alpine butter) on the milk fatty acid composition of lactating sows (as an animal model for lactating women) and on the growth performance of their progeny. The usual fat source of a standard lactation diet was replaced by either CLA-rich alpine butter or margarine (control diet). Compared with the margarine diet, feeding the alpine butter-supplemented diet increased (P < 0·001) the CLA concentration in the milk fat (742·3 (sd 272·0) v. 107·7 (sd 34·7) mg/100 g fat). Eleven of fourteen CLA isomers were higher (P ≤ 0·004) in milk fat after feeding the alpine butter-supplemented diet but the transfer was not proportional. The milk fat concentration of the sow milk and the level of SFA, MUFA and PUFA were not (P>0·05) affected. Growth performance of the progeny was similar for both dietary treatments. In summary, the findings show that adding alpine butter to the diet does not provoke a milk fat depression and does not alter the composition of total SFA, MUFA and PUFA in sow milk but increases its CLA concentration.