LIPID-COMPOSITION AND METABOLISM OF SUBCUTANEOUS FAT IN SHEEP DIVERGENTLY SELECTED FOR CARCASS LEAN CONTENT

Fatty acid synthetase and lipoprotein lipase activities, lipid content of adipose tissue and the fatty acid composition of subcutaneous fat, sampled by biopsy at the 13th rib, were measured in 20-week-old rams from lines of Texel-Oxford (TO) and Scottish Blackface (SB) sheep, bot h divergently selected for carcass lean content. A total of 150 animal s were measured, with close to equal numbers of animals per selection line-breed combination. In both breeds, the high (lean) selection line s had significantly lower backfat depths (TO: 0.5 mm and SB: 0.6 mm, s .e.d. 0-2) than the low (fat) lines. The lipid content of subcutaneous fat was 65 mg lipid per g fat tissue wet weight (s.e.d. 24) greater i n TO rams than in SB rams. The TO low line had a higher lipid content than the high selection line (426 v. 448 (s.e.d. 36)) and although the SB selection lines did not differ, the selection line with breed inte raction was not significant. SB rams had higher fatty acid synthetase activity (3.1 v. 2.6 (s.e.d. 0.3) on a log scale) but there were no di fferences between selection lines. Lipoprotein lipase activities were similar between breeds and selection lines. The lower concentration of myristic acid (C14:0) of TO rams compared with SB rams (0.9 (s.e.d. 0 .3)) was the only breed or selection line difference which was statist ically significant for fatty acid composition of subcutaneous fat. Lip id content of subcutaneous fat and lipoprotein lipase activity were hi ghly correlated and both were positively correlated with performance t est traits, especially with backfat depth. The correlation between bac kfat depth and fatty acid synthetase activity was not different from z ero. Performance test traits, lipid content of subcutaneous fat and li poprotein lipase activity were positively correlated with the unsatura ted fatty acids, with the exception of C18:1 when correlations were ne gative.