Fatty acids of adipose tissue,plasma, muscle and duodenal ingesta of steers fed extruded soybeans

Effects of feeding a high-energy diet that contained extruded soybeans on fatty acid composition of lipids of adipose tissue, skeletal muscle and plasma were determined for 18 Angus steers. Steers weighing an average of 309 kg were fed either a control diet or a diet containing 14.3% extruded soybeans and 6% fat until they weighed 474 kg. A third group was fed the control diet for the first half of the experiment and the soybean-containing diet for the rest of the experiment. Samples of blood, muscle (M. trapezius) and subcutaneous adipose tissue were obtained at 309, 368 and 427 kg of body weight; steers were slaughtered at 474 kg body weight, and samples of subcutaneous and perirenal adipose tissues,M. longissimus and blood were obtained. The lipids of subcutaneous adipose tissue taken at slaughter of all steers fed full-fat, extruded soybeans contained 24% more 18:2 and 18:3 than did those of steers fed the control diet. Extruded soybeans also caused an increase in 18:3 but only a slight increase in 18:2 in perirenal adipose tissue. The proportion of unsaturated fatty acids of lipids inM. trapezius increased slightly with dietary soybeans, whereas that ofM. longissimus was not affected. Lipids of blood plasma of soybean-fed steers contained a greater proportion of 18:2 and 18:3 and concomitantly less 14:0, 15:0, 16:1 and 17:0. Results indicate that feeding steers enough extruded soybeans to raise the fat content of the diet to 6% increases the proportion of polyunsaturated fatty acids of tissue lipids of cattle, and that this altered composition results from an increased amount of these fatty acids being available for absorption by the small intestine.