Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Science

First Advisor

F. C. Parrish, Jr.


Sensory, chemical and physical evaluations of bovine longissimus thoracis (LT) muscle were compared between bulls and steers (n = 299) of three frame sizes (small, medium and large), slaughtered following different times on feed (TOF)-180, 210 and 240 days. Bulls exhibited significantly lower (P < 0.05) marbling scores than steers. Palatability attributes were ranked lower (P < 0.05) for bulls while Warner-Bratzler myofibrillar force (WB-MF) and residual force (WB-RF) values were higher than for steers. Frame size had an impact (P < 0.05) on lipid, marbling and moisture contents for both sexes and fat thickness, tenderness, connective tissue, WB-MF and WB-RF for steers. TOF showed no significant change in marbling amongst bulls. Steers significantly increased in marbling between 180 and 240 days. Palatability remained unchanged for both sexes based on TOF. Small framed steers were most tender. Ultrasonic parameters showed extremely low R[superscript]2-values for palatability. However, R[superscript]2-values were higher for lipid and marbling parameters;Cholesterol and fatty acid composition of LT muscle were determined by gas chromatography-mass spectrometry and gas chromatography, respectively, following stratification by lipid content. TOF did not alter cholesterol content. A significant difference was observed for cholesterol based on sex and different lipid content groups. Cholesterol values reported herein are lower than previously reported results. Steers displayed a significant increase in C14:0 when fed 240 days. C18:0 content declined (P < 0.05) with TOF for bulls while steers exhibited this trend through 210 days on feed. Prolonging TOF revealed higher proportions of unsaturated fatty acids for both sexes. Lipid contents beyond 5% showed significant increases for C18:2 and significant decreases for C18:0 amongst bulls while steers showed significant increases in C18:1 and C18:2 for lipid levels greater than 3%;Sensory tenderness, flavor, WB-MF and myofibril fragmentation index of high pH meat were significantly different from normal pH control samples. Increase in WB-MF, lack of extensive degradation of muscle proteins and the decreased sarcomere length at pH 6.1 resulted in tougher meat than normal or high pH muscles. Gel electrophoresis of dark cutters revealed a lack in appearance of troponin-T to 30 Kd on 12% gels, and the appearance of a 'doublet' on 5% gels. This may account for the unusual tenderness observed.



Digital Repository @ Iowa State University,

Copyright Owner

Yunus Khatri



Proquest ID


File Format


File Size

199 pages