Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Science


A study was conducted to determine if beef steers fed a high-energy diet supplemented with extruded soybeans, enough for a diet of 6% fat, will increase the proportion of polyunsaturated fatty acids in lipids of adipose tissue, muscle and plasma. A control diet (C) and a diet supplemented with 14.3% soybeans (S) were fed to Angus steers from 309 to 474 kg body weight. A third group of steers was fed the control diet for the first half of the experiment (to approximately 386 kg body weight) and then switched to the soybean-supplemented diet (CS). Subcutaneous adipose tissue, muscle and plasma were obtained from each steer at average body weights of 309, 368, 427 and 474 kg. Cattle were slaughtered at 474 kg body weight. Subcutaneous and perirenal adipose tissues taken at slaughter from CS and S steers contained more 18:2 and 18:3 than did those of C steers. The proportion of unsaturated fatty acids of lipids in muscle of CS and S steers was only slightly increased. In response to dietary soybeans, lipids of blood plasma of both CS and S steers contained greater proportions of 18:2 and 18:3 than did C steers. Duodenal contents of Holstein steers fed each diet had similar proportions of all fatty acids; lipid percentage of ingesta from steers fed the supplemental soybeans, however, was greater than that from steers fed the control diet. This indicated a greater quantity of unsaturated fatty acids were available for absorption by the small intestine. Compared with the C steers at slaughter, in vitro fatty acid synthesis in subcutaneous and perirenal adipose tissues of CS and S steers was slightly decreased. The concentrations in plasma of total cholesterol and LDL-cholesterol were greatest for all steers fed the supplemental soybeans. Average daily gains, feed to gain ratios and feed intakes were not affected by the supplemental soybeans. Carcasses of CS and S steers, however, tended to contain more fat and had the greatest marbling scores. Those rib steaks from CS and S steers, however, had the least overall organoleptic quality.



Digital Repository @ Iowa State University,

Copyright Owner

Daniel Clark Rule



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198 pages