Purebred Beefmaster steers (n = 160) from five owners were fed at a commercial
feedlot in South Texas beginning in November of 2004; 68 steers possessed pedigree
information. Beginning in mid-November, steers were individually weighed and
evaluated for ultrasound body composition at 56-d intervals by a certified technician.
Feeder calf frame (FRM) and muscle (MUS) scores were assigned at initial ultrasound
evaluation. Steers were fed and marketed through a lean-based, branded beef program
and were harvested in two groups in May and June of 2005 at a commercial beef plant.
Analyses were conducted to investigate the ability to predict carcass traits from the
different sources of information available on these cattle. Evaluation of carcass traits
were investigated using four sets of independent variables referred to as sources A, B, C,
or D and ultrasound scan session (1 Â 4). An analysis included initial weight at first scan
session (IWT), FRM and MUS as independent variables through GLM procedures. B
analyses utilized ultrasound measures of the longissimus area, intramuscular fat, fat
thickness, rump fat, and gluteus medius depth along with IWT as independent variables.
Multiple regression was performed on each carcass trait using IWT and ultrasound traits
at each scan session. MallowÂs CP was used to select a model that best described each carcass trait. C analyses (GLM) utilized variables from A and B analyses combined plus
ranch. D analyses (GLM) included variables from C analyses plus sire nested within
ranch. Respective R-square values (scan 1 Â 4) for marbling score were .02, .04, .05, and
.10 using A information, .14, .17, .42, and .54, using B information, .35, .35, .47, and .55
using C information, and .56, .59, .65, and .76 using D information. R-square values
ranged from .34 to .86 for carcass weight, .11 to .77 for fat thickness, .06 to .82 for ribeye
area, and .10 to .81 for yield grade. Ultrasound data obtained closer to harvest and
increasing amount of data related to genetic and management background showed
increased R-square values, but may be best utilized in conjunction with one another to
predict carcass traits and final carcass value
