Holstein-Friesian bulls were slaughtered at 7, 14 and 19 months of age. Samples were collected from the psoas major, longissimus
and semitendinosus muscles. The total lipids (TL) of the samples were extracted and the fatty acid compositions were analysed by
gas chromatography. Both the slaughtering age and the type of muscles had significant effects on the intramuscular TL contents
and fatty acid compositions. The longissimus muscle had higher intramuscular TL both at 14 and 19 months than at 7 months of
age. As the bulls became older the proportion of saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) increased
in the TL of each muscle tested, whereas that of polyunsaturated fatty acids (PUFA) decreased. Among the muscle types, the
semitendinosus had the lowest, intramuscular TL at each slaughtering age and the psoas major the highest. Except for SFA at 7
months of age, the semitendinosus showed lower levels of SFA and MUFA and higher proportions of PUFA than the other two
muscles.