Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Science

First Advisor

Doyle E. Wilson

Second Advisor

Gene H. Rouse


Both steers (n = 497) and bulls (n = 247) were ultrasonically (RTU) measured for 12-13th rib subcutaneous fat thickness (UFAT) and longissimus muscle area (ULMA) just previous to slaughter. Carcass measurements collected by experienced evaluators were used as a basis to determine the accuracy of ultrasound measurements. Mean differences between carcass and ultrasound measurements suggest that carcass fat thickness (CFAT) was slightly underestimated (.032 cm) and carcass longissimus muscle area (CLMA) was overestimated by 1.47 cm[superscript]2 with RTU. The mean absolute value of the difference between CFAT and UFAT was.227 cm while this mean absolute difference was 5.09 cm[superscript]2 between CLMA and ULMA. Correlation coefficients between CFAT and UFAT and between CLMA and ULMA were.86 and.78, respectively. The standard errors of prediction corrected for bias were.29 cm for UFAT and 6.25 cm[superscript]2 for ULMA;A second study consisted of serially measuring performance-tested sire groups of Angus and Simmental bulls four times at 30-day intervals for weight (WT), height (HT) 12-13th rib ultrasonic fat thickness (UFAT), and ultrasonic longissimus muscle area (ULMA). These data were then used to evaluate compositional changes, adjustment procedures and to estimate genetic parameters. Linear as well as linear and quadratic regressions of each trait on age were performed on the pooled data and on an individual animal basis. These regression lines were plotted to assess the changes in each trait throughout the test period. Results suggest that mean individual animal linear and quadratic regression equations more clearly describe the compositional changes during the test period than linear regression equations. Comparing adjustment procedures involving one, two or all four measurements on each animal indicate that two measurements taken 30 to 60 days apart, when the contemporary group average age is near 365 days can provide accurate adjustment to a year of age. Single trait h[superscript]2 for 365-day adjusted WT, HT, ULMA for Angus were.52,.57 and.64, respectively. The same analysis of Simmental data yielded h[superscript]2 estimates of.37,.23,.21, and.87 for WT, HT, UFAT, and ULMA, respectively.



Digital Repository @ Iowa State University,

Copyright Owner

David Albert Duello



Proquest ID


File Format


File Size

202 pages