| Abstract: | Fatty acid composition and cholesterol content of muscle and adipose tissue from mature cows (N = 101) representing 15 breeds and crosses were determined. An initial group of cows was slaughtered after being fed slightly above the maintenance level for 2 wk; the remaining cows were fed either at the maintenance level or ad libitum for 84 d, then slaughtered. Samples of triceps brachii and longissimus muscle and subcutaneous and perinephric adipose tissue were obtained from each carcass. In addition, phospholipid and triacylglycerol fatty acids from total lipid extracts of triceps brachii muscle and subcutaneous adipose tissue were analyzed for 24 cows that were fed ad libitum or at the maintenance level for 84 d. Breed type effects on fatty acid composition were more pronounced in adipose tissue than in muscle tissue. Total lipid extracts of both triceps brachii and longissimus muscle from animals fed a maintenance diet for 84 d contained higher (P less than .01) percentages (3 to 8%) of polyunsaturated fatty acids (PUFA) and lower percentages (2 to 3%) of saturated fatty acids (SFA) than those from animals fed ad libitum for 84 d. This reflected significant variation in the fatty acids C14:0, C16:0, C18:2, C18:3 and C20:4 for both longissimus and triceps brachii muscle. Fatty acid composition within phospholipid and triacylglycerol fractions was similar regardless of maintenance or ad libitum feeding. Much of the variation in total lipid fatty acid composition appeared to be the result of differences in triacylglycerol:phospholipid ratios. Adipose tissue contained about twice as much cholesterol (mg/100 g wet weight) as muscle tissue. Both breed type and feeding group effects on cholesterol content of muscle tissue were nonsignificant. Values for cholesterol content of adipose tissue from cows fed restricted diets were higher than those from cows fed ad libitum (approximately 55 mg/100 g higher for subcutaneous and 25 mg/100 g for perinephric). The results show that changes in fatty acid composition of bovine tissues can be made genetically and by varying the energy level in the diet. Alteration of the cholesterol content of muscle tissue by these methods does not appear to be feasible. |
