Intramuscular fatty acid composition of neutral and polar lipids for heavy-weight Angus and Simmental steers finished on pasture or grain

Samples of 34 longissimus thoracis et lumborum from 78 heavy steers (41 Angus, 37 Simmental) finished on three feed types (26 on annual pasture, 25 on perennial pasture, 27 on 70% grain) were analyzed for fatty acid composition of triacylglycerols and polar lipids. High levels and a wide range of intramuscular lipid (105.8 g kg-1, SD = 34.8) were due to the very high mean carcass weight of 504.5 kg. Intramuscular lipid levels did not differ significantly between breeds or feed types. Significant differences between breeds and feed types were shown for most of the fatty acids measured in both triacylglycerols and polar lipids, with significant interactions for five polar lipid fatty acids. Levels of triacylglycerols and polar lipids were not affected by feed or breed. In addition to higher levels of 18:3, lipid from pasture groups also had higher levels of other n-3 acids including 20:5 and 22:5. Differences between the pasture groups were also found, but these were smaller than the differences between pasture- and grain-fed cattle. For several fatty acids, and particularly those in polar lipids, levels varied with overall lipid level. These results with very heavy cattle and a wide range of intramuscular fat levels show clearly that variability in intramuscular fatty acid composition may arise from differences in breed of cattle, feed type or lipid level in the muscle.