The effect of breed and different oil seed cake supplementation on milk yield, composition and milk fat fatty acid (MFFA) composition was studied using 12 Friesian and 12 Ayrshire lactating cows. Control diet contained maize bran (MB) plus minerals. For diet I and II, some of the MB in the control diet was replaced with cotton seed cake (CSC) (34.8%) and sun flower seed cake (SSC) (44.5%) respectively. Milk samples were collected for chemical composition analysis and butter making. The composition of fatty acid methyl esters (FAMEs) were analysed by gas chromatograph (GC). The data was analysed using Statistical Analysis System (SAS). The mean milk yield was significantly (P<0.05) higher in Friesian cows (8.36 kg/day) compared to Ayrshire breed (5.85 kg/day). The proportions of short chain fatty acids (SCFAs) were slightly higher (P>0.05) for Ayrshire breed (4.94%) compared to Friesian (4.34%). The proportion of medium chain fatty acids (MCFAs) for Friesian (12.73%) was slightly lower (P>0.05) whilst those of long chain fatty acids (LCFAs) (82.95%) were slightly higher (P>0.05) than those of Ayrshire (14.61 and 80.44) % respectively. The proportion of unsaturated fatty acids (UFAs) was slightly higher for Friesian (57.52%) than Ayrshire (46.03%) and for those fed CSC (57.42%) was slightly higher than those fed SSC (50.80%) and control diet (43.8%). The melting point (MP) range of milk butter fat (BF) in Friesian cows (39.5–41.5 oC) and (39.5–41.0 oC) was slightly higher compared to that of Ayrshire (39.5–41.0 oC) and (39.5–40.5 oC) when supplemented with CSC and MB diet respectively. It is concluded that both breed and oil seed cake supplements have no significant influence on the fatty acids (FAs) composition of BF